home

toc

**Chapter 2 Physics In Action**

Article on Sports with Physics

[] The article is about a soccer ball that was created for the world cup of 2010 that is suppose to make it bend unpredictably than any other ball. This new ball will have goalies guessing about which direction the ball is going to move in. Professor Derek Leinweber head of the school of Physics at University of Adelaide had this to say, "The Jabulani is textured with small ridges and 'aero grooves' and represents a radical departure from the ultra-smooth Teamgeist ball, which was used in the last World Cup". The physics behind it is there is something about the textures that makes this ball curve like no other ball. They have done tests between the Jabulani and a regular soccer ball and there is a significant difference between the two balls.

Chapter 2 Section 1
**What Do You See? 1 ** I see a kid kicking a soccer ball and it shows lines that they are going up and I see a kid shooting a ball that went over the net with the goalie watching it go over.

**What Do You Think? 1 ** -With the ice skater on the ice it is the lack of friction on the ice along with the momentum of the skater moving forward. With the soccer ball it is the same concept with the ice skater. But also once an object is in motion it takes an object or obstacle to stop it.

**Investigate 1** Hypothesis: The steeper the incline is, the higher the object will travel on the other side. The ramp is a parabola, making the initial hight a key component to figuring out what the maximum height is on the opposite side. 1. Initial height: 7.00m 1e. The height opposite of the original side: 7.00m 2a. The maximum height will be the same all due to the initial height. Even though the slope is not as steep it will still travel the same height. 2b. Yes, when the skater started at 7.00m, he went to the same height and will not have enough momentum to keep going. 3. My prediction was close 3b. The height that the object starts at will be the highest point throughout. 4a. With a less steep slope, the height will still remain the same no matter what. 4b. Prediction is same as outcome. 5a. No, no slope to reach the maximum height. 5b. The force/momentum will take it until an obstacle comes in contact. 5c. Momentum keeps the ball on track. 5d. The skater rolled off the ramp. 6a. The length increases. 6b. It will remain the same to the initial height. 6c. The heights are always equal. 6d. The skater will move until another force acts on it.

**Physics Talk 1** **Newton's FIrst Law of Motion** **Galileo's Law of Inertia** Galileo: An Italian physicist, methematician, atronomer, philosopher, father of modern science. -Observed a ball rolling down a ramp to find out that it went the same height when it rolled up another ramp. -imagined a ball made of really hard material on a horizontal surface. He came to the conclusion that the ball would continue its motion with a constant speed along a straight line (forever). -An object remains at rest unless something causes it to move. **Inertia:** The tendency of an object to remain at rest or to remain moving with a constant speed in a straight line. - Moving objects will continue to move unless a force stops them. - Newton used Galileo's law of inertia - Is a property of matter **Newton's first law of motion:** in the absence of an unbalanced force, an object at rest remains at rest, and an object already in motion remains in motion with a constant speed. **Mass:** the amount of matter in an object, or tendency to resist a change in motion. - Speed is not important when determining inertia - Mass is how we measure inertia. **Running Starts** speed: the change in distance per unit of time velocity: speed in a given direction acceleration: the change in velocity per unit of time Kicker for football has a running start, he runs up to the ball kicking it as far as he can. **Frames of Reference** If you run a ball prior to throwing it, the ball gets your speed before you even try to release it. frame of reference: a vantage point with respect to which position and motion may be described speed is always relative to something

**Checking Up 1** 1. inertia: the natural tendency of an object to remain at rest or to remain moving with constant speed in a straight line. 2. Newton's first law of motion: in the absence of an unbalanced force, an object at rest remains at rest, and an object already in motion remains in motion with constant speed in a straight-line path. 3. A force is needed to act on an object to stop it from moving at a constant speed. 4. A frictional force that you can not see stops this object. 5. The one with greater mass will have a greater inertia. 6. Frame of reference is important because you need a perspective. It is the respect to which position and motion may be described.

**Physics To Go 1** 1a. The ball will role forever. 1b. An object already in motion remains in motion with a constant speed. 2. 20 cm 3. No, friction will always be present when there is gravity. So no object can role forever and ever in the real world. 4. The hockey puck will remain in motion at a constant speed with a small amount of friction being applied to it on the ice until an object/obstacle hits the moving puck. 5. 2.5m + 4.5m = 7m/s 6. 10.3 + 4.2 = 14.5 m/s 7a. 5.6 + 2.4 = 8 m/s forward 7b. 5.6 - 2.4 = 3.2 m/s forward 7c. V = square root 5.6^2 + 2.4^2 = 6.1 m/s @ 67º or 23º from train's direction. 8. 85 m/s - 18 m/s = 67 m/s 9a. 15 cm / sin (45º) = 21.2 cm 9b. 15 cm / sin (20º) = 43.9 cm 9c. 15 cm / sin (15º) = 58 cm 9d. 15 cm / sin (5º) = 172 cm 10a. Soccer: When the ball is not touched, it is at rest. When it is kicked it will not stop until another player or goalie hits it. Hockey: The puck is at rest until someone hits it with their stick. It will stay in a straight line until another stick hits it or goalie catches it. Football: ball is at rest until the kicker kicks the ball, then it goes straight until it goes through the field goals. 10b. Sportscaster Soccer: Taylor runs up to the ball and kicks it with all his might, going straight through all the other players. Unfortunately the goalie stops him and the ball is put to rest. Hockey: Scott slapshots the puck in a straight line at the goalie, it looks good but oh the goalie blocks his shot. Football: Chris Bickel goes to kick the ball from a running start, it looks good. It's a field goal and now the ball is at rest.

What Do You Think Now? 1 1. Ice skaters can move across the ice for a long time because there is barely any friction to stop them. They move in a straight path without any unbalance force stopping them. 2. Soccer balls continue to roll across the field because the object is in motion and remains in this motion with a constant speed. (Newton's law) The ice skater's speed is determined by their skating start. The speed + the speed they used to push off. The soccer ball's speed is determined by the running up to the ball + the speed the ball was kicked at. Because of Newton's law, they keep moving until an unbalanced force interferes.

**Inquiring further 1** Sources: scienceblogs.com/builtonfacts/.../the_physics_of_curling.php ; en.wikipedia.org/wiki/Slide_(baseball) 1. Curling is demonstrated that you push a stone down the ice using brooms to slow it down and know an opponents stone out of the "house" That is how you scored points. 2. Baseball players run through the base because if you need to run to the next base you need to stay on your feet. You slide when going to second or third base to get to the bass without getting caught stealing.

Chapter 2 Section 2
Three sports where there is motion with constant speed Hockey: The puck that gets hit by the stick travels at a constant speed. Soccer: The ball is kicked and travels at a constant speed lacrosse: The ball is thrown and flies through the air at a constant speed.

What Do You See? 2 I see a snail and a dog with a boy behind it all walking at a constant slow speed. In the other picture there is a boy running at a fast constant speed and the dog running at a constant speed. The boy's speed is faster so he might pass the dog.

What Do You Think? 2 I think 45 m/s and 100 mi/h are the speeds of the baseball from when it was thrown to when it was caught. These speeds are from the windup of the pitcher to the speed of which he throws it.

Physics Talk 2 acceleration: a change in the velocity of an object over time. Average speed is the constant speed in which you are traveling. -Measured in (m/s) Average Speed: The distance traveled / the time it took to travel that distance Speed is a ration of distance traveled by the time taken. Vav = delta d / delta t instantaneous speed: the speed measured during an instant: the sped as the time interval approaches.

Checking Up 2 1a. Constant speed: the distance between ticks were equal in length. 1b. Positive acceleration: when gradually increasing speed, the distances between the dots gradually get longer. 1c. negative acceleration: when gradually decreasing speed, the distance between the dots gradually got smaller. 2. Vav = change in distance / change in time; Vav = 400m / 50s = 8m/s 3. Instantaneous speed is the speed of a single instant and average speed is the average speed of several instances. 4. A = change in v / t; A = 166 2/3m/s / 10; A = 16 2/3 (m/s)/s

Physics To Go 2 1. Instantaneous speed is the speed at single instant or second. Average speed is the average of several speeds/instances. 2a. Vav = d/ t ; 1000m/15s ; Vav = 66.7 m/s 2b. Vav = d/ t ; 84m/6s ; 14 m/s 2c. Vav = d/ t ; 9.6 km/ 2 hr; 4.8 km/h 2d. Vav = d/ t ; 400km/4.5h; 89 km/h 3a. Negative acceleration (slowing down) 3b. positive acceleration (speeding up) 3c. no acceleration 3d. negative acceleration 3e. no acceleration 3f. no acceleration 4a. graph with a constant increase in speed: a, d 4b. graph with a constant speed: b 4c. graph with a greatest change in speed: a, 4d. graph with an increase then a decrease: c 4e. acceleration of: student a: positive constant student b: no acceleration student c: increasing and then decreasing student d: positive acceleration 6a. (45 km)(1000m) / 360 s = 125 m/s A = -125/9 = 14 m/s^2 It has a negative value 7a. constant speed 7b. increasing speed (positive) 7c. constant, increasing, decreasing, constant 7d. decreasing, constant, increasing 8. V = 100 mi / 2h = 50 mi/h 9. No because if the average speed was 15 m/s, the instantaneous speed is not always 15 m/s. The average is what takes the final speed and the initial speed and averages them together, which is 15. The instantaneous takes one speed, so it could be either 15 or 12. 10. x.x..x......x.........x...........x.............x.............x.............x Accelerating Constant 11. The car was 20 m/s more every 5 s. 14. sports with similar ticker-tape patterns a. constant at an average speed: soccer when the ball is kicked b. constant at a fast speed: running a race c. constant at a slow speed: golf when close to the hole d. positive acceleration: long distance running: start slow and then quickly increase speed at the end e. negative acceleration: back stroke in swimming

Physics Plus 2 Rebounding = change direction Even when speeds are small, accelerations are huge if the bounce times are tiny.
 * Velocity || Acceleration || Example ||
 * Small || Small || turtle ||
 * Big || Big || Racecar, Airplane, Roket ||
 * Small || Big || Rabbit, deer, Dog Rebounding (any object) ||
 * Big || Small || Truck ||



What do you think now? 2 100 mi/h and 45 m/s are both instantaneous speeds. They are measurements for velocity, being that they measure the distance in relation to time. You could find velocity by dividing distance traveled by elapsed time.

Chapter 2 Section 3
What do you see? 3 I see a person walking with a stick pushing a ball that is right on the stick going at a very slow speed. Then the person begins to run and try to move a ball from the bottom of the stick but is still moving right in front of it. The person then moves faster and the ball pushes up the stick.

What do you think? 3 1. Force is a push or a pull 2. The same force will move the bowling ball with more ease because it has a much lower mass.

Physics Talk 3 Equation for Newton's Second Law of Motion: Acceleration = force / mass a=F/m ; F=ma ; m=F/a -2nd law: Accelerations are caused by unbalanced forces -if you observe an acceleration (change in velocity), then there is a unbalanced force causing the acceleration -a force to an object with a small mass, the acceleration is large -a force to an object with a large mass, the scceleration will be smaller -acceleration gets less and less as the mass gets larger and larger -even when it seems acceleration is zero, that is not true bc Newton's law is always valid -acceleration of an object is directly proportional to the applied force and inversely proportional to the mass Sample Prob: As the result of a serve, a tennis ball (mt = 58 g) accelerates at 430 m/s^2 for the very bried time it is in contact with the racket F = mt(a) = (.058)(430) = 25 N -zero between nonzero digits - yes -zero at the end of a decimal number - yes -zero at the beginning of a decimal - no -large number w/o a decimal point - no Gravity, Mass, Weight, and Newton's Second Law weight: the vertical donward force exerted on a mass as a result of gravity equation: Fgravity = (m)(Agravity) ; W = mg m = kg ; g = acceleration due to gravity -when two forced act at the same time, the direction as well as the magnitude of the forces determine the motion of the object -the the forces are in the same dirction, then the sum of the forced or net forcecould be zero and there would be zero acceleration -free-body diagram: a diagram showing the forcs acting on an object -when you hold an object in your hand, it does not move or accelerate downward. There is the force of your hand pushing up on the object UP: force of hand on apple DOWN: force of gravity on apple -car on highway: force of the road on the tires moving it forward. force of air resistance is applied against the vehicle. Checking Up 3 1. Newton's second law of motion is acceleration is equal to the force divided by the mass. 2. The greater the mass, the smaller the acceleration of the object. 3. If an object weighs 30 N. Weight is the vertical donward force exerted on a mass as a result of gravity. The force is 30 N. 4. On a planet with a higher acceleration, your weight would increase, but your mass would remain the same.
 * Where There's Acceleration, There Must Be an Unbalanced Force**
 * Significant Figures**
 * Balanced and Unbalanced Forces**

Notes from Class Today (11-17-10)



Physics To Go 3 1. a.350N, b. 80 kg, c. 10 m/s^2, d. 80 kg, e. -15 m/s^2, f. -3000N 3. F = (m)(a) ; 42N = (.30kg)(a); a = 140 (m/s)/s 4. F = (m)(a) ; F = (.040kg)(20m/s^2) ; F = 0.8N 5a. Newton's first law of motion: A bowling ball has a larger mass than a baseball, therefore the inertia is greater. A greater force than a human would need to throw the bowling ball really fast so it continues at a fast speed. The baseball has less inertia but will travel in a straigh-line of motion for longer and a greater force because it is easier for the force of the human bodies to accelerate it. 5b. Newton's second law of motion: In the equation F = ma, Mass and acceleration are indirectly proportional. When a baseball with less mass will have a faster acceleration than a bowling ball, therefore it is going faster when it hits your hand. 9. When throwing a ball, the force of your hand is acting upon the ball until an unbalanced force comes in contact with it. 10. 50N + 40N = 90N 11. 4 adults x 200N each = 800N 12. F=am; 125N =a(.7kg); 179 m/s^2 13. Resultant Force: 130N north east 14. Resultant Force: 6403N to the side @ 39° 15. F=mg ; F=(12.8kg)(9.8m/s^2) F= 125 N 16a. 10N + 40N = 50N @ 53° 16b. f=ma; 70N = (5.6kg)a a = 8.9 m/s^2 17a. 36N @ 34° 17b. f=ma; 36=100kg(a) a = 0.36 M/S^2 17c. 50N = 100kga a= .5 m/s^2 18. Sports announcer: A tennis ball of .057kg was just served, the ball is accelerating at 430 m/s^2. What a great serve! that was due to the server's swing and the total body force of 24.51N.

Work for Physics to go and physics plus Physics Plus 3 1. 125 NW @ 45 degrees a. resultant force: 0N b. 81 N c. direction of net force: NW  What do you think now?
 * Force is a push or a pull
 * Mass and acceleration are indirectly proportional. So with, the same force, the bowling ball, which has more mass, would have a lesser acceleration. The baseball, with a smaller mass, would have a greater acceleration. The small the mass the greater the acceleration. The greater the slower the acceleration.

Chapter 2 Section 4
What Do You See? 4 I see a boy who is timing how long it takes for the apples to fall when the girl drops them. The apples are evenly horizontal its just the perspective of where they are falling are different.

What Do you think? 4 I think things such as the maximum of where it is thrown. How fast the object is going, also what angle it is thrown at.

Investigate 4 1a. Yes, they both hit the floor at the same time 2a. Yes, they both hit the floor at the same time again. 3a. No, speed does not matter because all speed effects is the distance that the coins travel. 3b. Yes, the faster the speed is, the further the coin goes. 3c. 4a. Changing the height does not make the coins hit the ground at different times, but it positively effects the horizontal distance. The faster and higher it is the further the one coin will go.

Part C:

Physics Talk 4
 * Trajectory - path
 * Projectile - an object acted on only by gravity.
 * The x - component and y - component of all vectors are independent.
 * Vertical velocity affects vertical distance
 * Horizontal velocity affects horizontal distance
 * Time for a projectile to reach the ground (hang time) is the same as the time it takes to drop.
 * Acceleration is due to gravity -9.8 m/s^2
 * Vertical velocity changes by -10 m/s every second.
 * Horizontal Velocity does not ever change.
 * Throwing horizontally results in the same trajectory as the second half of the path of a ball thrown at an angle.

Checking Up 4 1. With the exception of free fall, mass does not affect an object so they fall at the same speed. 2. No, it increases -10 m/s every second. 3. 0, and the balls acceleration is -9.8 m/s

PTG 4 1. X........... X X.................X X......................X X .........................X 2. X.........................X X................................X X......................................X X ..........................................X 4. Everyone believes that a bullet dropped and one that shot horizontally will arrive at the ground at different times because they believe that the velocity will keep it in the air longer. But really they will hit the ground at the same time, the vertical velocity is the same, but the horizontal velocity is different. 6. A projectile's horizontal motion has no effect on its vertical motion, and vice versa. Vertical velocity changes by -10 m/s every second. Horizontal velocity does not change ever. Vertical changes, and Horizontal does not. We see that by the stair case way of drawing the curve. 7. Both arrows will take the same time to strike the horizontal plane.

8. 3.6 m/s @ 33.7 degrees 9a. 11.98 m/s 9b. 23.96 m 10a. 8.5 m/s 10b. 4.25 m 11. The pitcher has just thrown the baseball at a 25 degree angle above the horizontal at a velocity of 80 m/s from the ground. Horizontally, it has no acceleration, but vertically it has an acceleration of -9.8 m/s/s. The time it takes to reach the batter was just 3 seconds! After these three seconds, the ball was traveling at 72.5 m/s wow!

Physics Plus 4

Video Clip

http://www.youtube.com/watch?v=ybEs3j_MmrA

If you watch the two long jumpers jump. You will notice that they actually get far because they are jumping high and not because they are jumping far. Their hips are raising causing the jumpers to extend their legs and making their range of motion much larger allowing them to jump very far. The only projectile in this video is when the jumper takes off gravity eventually pulls them down and the trajectory is the runner. To find all the information, you would need to calculate their hang time, acceleration, and vertical velocity.

What do you think now? 4 It all depends on where the object is thrown and how fast the object is thrown and the momentum that the object has, the launch velocity and the initial height and speed.

Chapter 2 Section 5
What do you see? 5 I see a ball that is kicked up, it bounces off the boy's head and goes up then down.

What do you think? 5 1. Smaller angles have longer rang velocities and are up for a short amount of time, larger angles have mall ranges and are up for a long amount of time. 2. The greater the speed, the faster the object will travel, so the range is longer.

Physics Talk 5 Modeling Projectile Motion Projectile has two motions that act at the same time and do not affect one another -One motion is constant along a straight line (affected by launch speed and direction -second is downward acceleration at 9.8 m/s/s. (affected by launch)  Mathematical Model: table of times, speeds, and distances during falling  Physical model: the evenly spaced strings of calculated lengths  Without air resistance, all trajectories are parabolas  DiagramL trajectories launched at different angles but with the same speed  all balls travel in parabolas  -a 45 degree launch produces the greatest range (longest distance)  -pairs of angles (add up to 90) are identical distances  small angles have greater horizontal velocities but are up for a shorter amount of time  large angles have smaller horizontal velocities but are up for longer amount of time  Exceptions: curve balls, temperature

Checking Up 5 1. Two types of motion: constant and downward acceleration. 2. For a model to be accepted, it must match the reality in nature. 3. Height and range with different angles: a 45 degree launch produces the greatest range, pairs of angles (add up to 90) are identical distances.

PTG 5 1. 45 degrees because the object will go the farthest. 2. When greater than 45 degree angles, the less far the object will go. 3a. 90 degrees- 30 degrees = 60° 3b. 90 degrees- 15 degrees= 75° 4. It is a human error because it is not possible to launch yourself at a 45 degree angle. 5. When you jump high, you are good at the long jump, thats why he was probably good at it because longer time spent in the air = more distance. 6a. At point x, a = g = -9.8 m/s^2 down 6b. The direction of its velocity at x is east. 7a. vertical speed final: 29.4 m/s 7b. horizontal speed at one second: 5.0 m/s 7c. distance from cliff: 15 m 8. 45 degrees would give it the longest range. 9. The angle that produces the greatest projectile height would be the one closest to 90 degrees. 10a. the direction of acceleration is down 10b. seconds to reach ground: d = vit + .5at^2 = -200 / -9.8 = 4.5 s 10c. distance from cliff: 90m dx = vixt + 1/2at^2

Physics Plus 5

What do you think now? 5 A 45 degree angle gives the longest range but is not physically possible. Anything bigger gives you more time in the air but a shorter range. Any two complementary angles can give you the same range. A greater launch speed of a projectile might change the range when the launch angle is the same because if it is launched faster it is going to go farther.

Chapter 2 Section 6
What Do You See? 6 I see a person that is on a chair that has wheels on it with his feet on the wall. I see him pushing off the wall and flying back really fast with the chair on the floor and he is still in it.

What Do You Think? 6 If i were to tell someone how to jump, I would tell them to stand straight, bend their knees then explode off the ground so the force would push them forward using gravitational force.

Notes Newton's Laws of motion 1. An object at rest will stay at rest, and an object in motion will stay in motion at constant speed in a straight line, unless an unbalanced force acts on it. Things won't change motion unless forced to. 2. Acceleration is directly proportional to net force and inversely proportional to the mass of the system. A = f/m 3. Every action has an equal but opposite reaction. All forces come in pairs but act on 2 different systems.

Physics Talk 6 Newton's Third Law of Motion: -for every applied force, there is an equal and opposite force. The two forces always act on different objects -Forces are always equal in the opposite direction -forces come in equal and opposite pairs -push on the wall and the wall pushes back with the SAME force and you can't make the forces unequal Inanimate Objects can Push Back: -objects can apply force due to mass and gravity. -free body diagram: a diagram showing the forces acting on an object -when standing, your mass is pulling you down. If not for an equal force from the floor that was going up, you would fall down. Challenging Newton's Third Law how something/someone can Pull something/someone ex: person on wheely chair person pulls on chair w/ small force. The chair pulls back on person with equal small force. The one force on the chair makes it move forward. Two forces on the person--one of the ground and other of chair, which are not equal. Ground force is larger making the person move forward.

Checking Up 6 1. Every action has an equal but opposite reaction. All forces come in pairs but act on 2 different systems. 2. Earth pulls down a mass with the force of gravity. The mass pulls ip on the Earth with an equal force of gravity. 3. A free - body diagram shows the force acting on an object.

PTG 6 1. Yes, because every action has an equal but opposite reaction. 2. No, The chair knows how much to push up by how much we push down on it. Every force has a partner and is the same. 3. The bathroom scale measure weight / force by the simple equation of m times gravity. It measures the mass of the body exerting a force on the scale and multiplies it by the acceleration of gravity on Earth. 4.) The forces on each other are the same, but the acceleration of the ball is much greater than the bat. The accelerating ball collides with the bat, which may have a lower mass, and break it. 5.) When a big football player hits a small running back they are both exerting the same force on each other. But, since the mass of the running back is smaller, and the acceleration of the bigger player is larger, the smaller guy will move into the direction that the larger guy was going. 6.) Normal force of person on boards and boards on person. And weight of the person to Earth and boards to Earth. There is no friction because of the ice. 7.) Baseball players perfer to wear gloves when catching a ball because all forces come in pairs so when the ball hits the players glove, their hand is going to need to exert the same force on the ball. 8a.) Oh my gosh, the long jumper just crashed right into the sand and what a crazy fall he just made. This is because the force he exerted to the ground made it hard of an impact toward his face. 8b.) A deflection of the ground can produce a force if you were to fall. During the fall, you would be pulling up the force from the ground while pushing down the force of your own. I would make this more exciting by showing a clip of a soccer player tripping, and falling and commenting on it with enthusiasm.

What Do You Think Now? 6 I would tell him to bend his knees and then jump as vertical as he can. I would tell him to use his arms and propel himself up by driving his knees up.

Chapter 2 Section 7
What Do You See? 7 I see that the boy can push the shoe on the ice a lot easier than the shoe on the sand.

 What Do you Think? 7
 * Because certain shoes help you get friction on certain areas, without this type of shoe we would not be able to play on this surface without injuring ourselves.
 * Spikes in track help you run on your toes which help you run faster which helps you beat people in a race.

Physics Talk 7 Friction  Analyzing the Forces Acting on the Shoe  -friction: a force that resists relative motion between two bodies in contact <span style="font-family: Tahoma,Geneva,sans-serif;"> -2nd law: vertical forces on the shoe must add up to zero The downward force of gravity on the shoe must be the same as the upward force applied to the shoe by the surface <span style="font-family: Tahoma,Geneva,sans-serif;"> normal force: the force acting perpendicularly or at right angles to a surface <span style="font-family: Tahoma,Geneva,sans-serif;"> (equal in force and ipposite in direction to the shoe's weight) coefficient of sliding friction: a dimensionless quantity; its value depends on the properties of the two surfaces in contact and is used to calculate the force of friction -the force of friction is = force required to slide the oject on the surface with a constant speed

<span style="font-family: Tahoma,Geneva,sans-serif;">Checking Up 7 <span style="font-family: Tahoma,Geneva,sans-serif;">1. The force of friction is equal to the force reading on the spring scale because the pulling force applied was equal to the frictional force, and since the two forces were in opposite directions, the net or total force due to them was zero <span style="font-family: Tahoma,Geneva,sans-serif;"> 2. coefficient of sliding friction has no units because it is a force divided by a force <span style="font-family: Tahoma,Geneva,sans-serif;"> 3. the force of friction is = force required to slide the object on the surface with a constant speed

PTG 7 <span style="font-family: Tahoma,Geneva,sans-serif;">1. In basketball, athletes want to have more friction to have better footing. If it is raining outside, or the court is icy, the athlete would want to increased the friction. They should buy some type of shoe with a heavier mass because with a heavier mass this will create more friction. <span style="font-family: Tahoma,Geneva,sans-serif;"> 2. In snowboarding, athletes want to have the least amount of friction. To reduce friction, they wax the bottom of the board to reduce friction. <span style="font-family: Tahoma,Geneva,sans-serif;"> 3. No, she will not know if her shoes will provide the same amount of friction on a court outside of her home. She needs to know the material of court, the roughness, and how it will react with your sneakers. <span style="font-family: Tahoma,Geneva,sans-serif;"> 4. Tennis players have different shoes for clay, grass, and hand surfaces. For the hard surfaces, their shoes don't need to provide as much friction. On the clay courts, which are more slippery, the shoes need to provide more friction. For grass, the shoes need to provide less friction. <span style="font-family: Tahoma,Geneva,sans-serif;"> 5. .03 = __ / 600 N. The minimum horizontal force would have to be 18 N to keep the skier coasting at constant speed across level snow. 6a. W=mg ; W=(1000)(9.8) ; W=9800 N 6b. mu=f/N ; .55=f/9800 ; f=5390 N 6c. Fx=MAx ; f=ma ; -5390=1000a ; a= -5.39 (m/s)/s 6d. Vf=Vi+at ; 0=Vi+(-5.39)(6) ; Vi = 32.34. Change in speed: 32.34 m/s 6e. Original speed: 32.34 m/s. The driver's claim was wrong. He was going faster than he should have been driving: 32.34 m/s and he said he was driving 29m/s.

<span style="font-family: Tahoma,Geneva,sans-serif;">7. Air and water have affects on motion similar to sliding friction. Air resistance and water resistance remain constant, but it is the speed that is hanging. When I am running and my speed is getting faster and fastr, the same wind resistance is hitting my face. <span style="font-family: Tahoma,Geneva,sans-serif;">8. When there is a max, force it will set a limit on how fast you start. Even if you have strong legs, your acceleration would be greater. To solve this problem, we can reduce friction by buying shoes that have a smooth surface. <span style="font-family: Tahoma,Geneva,sans-serif;">10. Without any friction we could not walk and that would be a huge problem. No friction = no movement, you would slip and fall every time you got up. 11. We are here at the basketball game and the players are wearing new shoes. They claim that the shoes are a little heavier so there is more friction, to keep them grounded. In basketball, players can't slip around the court and need to be sure-footed. These shoes will running around the court, exert a force in the direction the player is running, it also provides the force of gravity, and a normal force up from the ground.

<span style="font-family: Tahoma,Geneva,sans-serif;">Physics plus <span style="font-family: Tahoma,Geneva,sans-serif;">

<span style="font-family: Tahoma,Geneva,sans-serif;">Lab Bowling With Blocks

<span style="font-family: arial,helvetica,sans-serif; font: normal normal normal 12px/normal Helvetica; margin: 0px;">1. The coefficient of friction in Part I displays the friction/forces against each other between the block and the floor. <span style="font-family: arial,helvetica,sans-serif; font: normal normal normal 12px/normal Helvetica; margin: 0px;"> 2. My mu was .375 and the class mu was .325. The percent difference is 15.38%. The results do not have to be the same because of random errors or systematic errors. <span style="font-family: arial,helvetica,sans-serif; font: normal normal normal 12px/normal Helvetica; margin: 0px;"> 3. My times were pretty comparable. They were all lower than the actual calculated times. Highest: 24.9% and Lowest: 18.9%. <span style="font-family: arial,helvetica,sans-serif; font: normal normal normal 12px/normal Helvetica; margin: 0px;"> 4. The theoretical physics we are doing in class applies to the real world because most sports we play display this Neweton law. Bowling for example, contains the coefficient of friction. <span style="font-family: arial,helvetica,sans-serif; font: normal normal normal 12px/normal Helvetica; margin: 0px;"> 5. 3 sources of experimental error: if the tape measurer was on a slant, the distance could be thrown off. If the the floor has bumps, it can throw off the acceleration. Finally, if the stop watch was not stopped/started quick enough, the calculations for part II would have errors.

Fx = max ; f=max ; .75=.189a = .25 m/s^2 Fy = may ; N-W=0 ; N=W ; W=(.189)(9.8) ; W=1.85N Mu=f/N ; .28 = f/1.66 ; f=.46N Vf^2 = Vi^2 +2ad ; -Vi^2 = -24.84 ; 0=Vi^2+2(-2.7)(4.6) ; Vi = 5.0 (repeat for 3 trials) For all errors: (calculated time-measured time / calculated time) x 100 <span style="font-family: arial,helvetica,sans-serif; font: normal normal normal 12px/normal Helvetica; margin: 0px;">Part I

N || Mu || Class Avg. Mu || % Difference ||
 * Tension N || Tension N || Tension || NFf(N) || Total Weight
 * .75 || .75 || .75 || .75 || 2 || .375 || .325 || 15.38 ||

Part II

What Do You Think Now? 7
 * Mass (g) || Mass (kg) || Measured Time (s) || Measured Distance (m) || Ff (N) || Acceleration (m/s)/s || Calculated Vi (m/s) || Calculated time (s) || % error ||
 * 189.79 || .189 || 1.43 || 5.33 m || .75 || -.25 || 5.0 || 1.85 || 24.9 ||
 * 189.79 || .189 || 1.79 || 6.85 m || .75 || -.25 || 5.7 || 2.11 || 18.9 ||
 * 189.79 || .189 || 1.59 || 6.6 m || .75 || -.25 || 4.48 || 1.66 || 23.5 ||  ||
 * 189.79 || .189 || 1.59 || 6.6 m || .75 || -.25 || 4.48 || 1.66 || 23.5 ||  ||
 * Certain shoes are made in certain sports because they require a grip on certain surfaces. Without the grip at the bottom of the shoe there would be no grip towards the friction and you would slip and slide everywhere.
 * Think of track you need grips on your shoes to plant your feet when jumping towards the pit.

Chapter 2 Section 8
What do you see? 8 I see a person trying to pole vault his way to the top of the party on the roof. I see he is going really fast and trying to make his way to the top.

What do you think? 8 The pole size is equivalent to how much the person can hold his upper body strength to the pole. Sure the pole may be as high as the bar but that doesn't mean the person is strong enough to lift himself that high. Factors such as speed, strength of the person, and the height.

Investigate 8 a. The more you pull back the higher the penny will go. b. The further off the table the ruler is the higher the penny will go the more or less the ruler can be bent will depend on whether the penny will go high or low. Position of the penny closer to end also affects it. 1a. Will the mass of the coin affect the height the penny will reach. 1b. The maximum height of a penny, nickel, and quarter three times each. 1c. Meter stick 1d. Making a comparison between the three coins.

Trials (mass of coin) Penny Nickel Quarter 35 22 20 34 29 23 40 24 19'

<span style="font: normal normal normal 13px/normal Arial; line-height: 19px; margin: 0px;">Physics Talk Summary 8 Law of Conservation of Energy a force can change the position and speed of an object in a way that allows the position and speed to change back Kinetic energy- energy associated with motion gravitational potential energy- energy an object possesses because of its vertical position from Earth potential energy- energy associated with position SUM of potential and kinetic remains constant Law of Conservation of energy: energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant Energy and Work while a ball is rising or falling, the sum of gravitational potential and kinetic energy remains constant work- the product of the displacement and the force in the direction of the displacement (physics quantity that equals the force multiplied by the distance) Conservation of Energy in the Pole Vault elastic potential energy- the energy of a spring due to its compression

<span style="font-size: 12px; font: normal normal normal 13px/normal Arial; line-height: 19px; margin: 0px;">Checking Up 8 1. A force is the reason for energy to change. 2. The penny gets its energy from a ruler that has elastic potential energy. 3. The vaulter's kinetic energy is used to catapult him with an inital speed upward and the remaining kinetic energy is turned into elastic potential ernergy as the pole bends. 4. Joules is the unit of work.

PTG 8 1. The shot put is launched by hand which is work and is increasing speed which is kinetic energy. In the air, while picking up speed & changing speeds, there is kinetic energy. That is turned into gravitational potential energy as the shot put is thrown above its starting position. The ball eventually drops and the ground stops it through work. 2. The golf ball stays at rest and then is hit by a club which is work. The ball travels and increases speed which is kinetic energy. When above its surface, the ball has gravitational energy. On the way down, there is kinetic energy. After, the ground then causes the ball to stop which is work 3. KE = GPE 1/2mv^2 = mgh 1/2(12)^2 = (9.8)h 7.3 m = h 4. The length alone can not determine the limit of vaulting height. Food energy gives muscle the energy for the person to run. That gains kinetic energy, which catapults the vaulter with an initial speed. Then that energy is converted into elastic potential energy when the pole bends. When the pole straightens, that energy is turned into increased gravitational potential energy. 5. The pole would increase temperature as the vaulter does work on the pole with first kinetic and then elastic energy. But at the pule straightens, it will decrease in temperature as the vaulter increases his/her gravitational potential energy 6. KE = GPE 1/2mv^2 = mgh 1/2v^2 = (9.8)(4.55) v = 9.44 m/s 7. KE = GPE 1/2mv^2 = mgh 1/2v^2 = (9.8)6.14 v=10.97 m/s Sergei's speed is higher than Emma's speed. 8a.) GPE = KE mgh = 1/2mv (9.8)(100) = 1/2v v = 1960 m/s 8b.) You don't need the mass of the rock because it cancels out 9.) Wpullback = EPEf W = 1/2kx^2 W = 1/2(1500)(.25)^2 W = 46.875 9b.) EPE = KE 1/2kx^2 = 1/2mv^2 1/2(1500)(.25)^2 =1/2(.1)v^2 v=30.6 m/s 10a.) EPE = W 1/2kx^2 = F x d 1/2(315)(.3)^2= W 14.2 = W 10b.) 14.2 = F x .3 47.3 N = F 11.) GPE = EPE mgh = 1/2kx^2 .04(9.8)(1)=1/2(18)x^2 x = .21 12a. F (measured in N)= m(measured in kg) x a(measured in m/s^2) . Therefore 1N = 1kg x 1m/s^2 12b. GPE=mgh ; (kg)(m/s^2) ; 1kg x 1 m/s^2 = J 12c. KE=1/2mv^2 ; 1/2(kg)(m/s)^2 ; 1kg x 1 m/s^2 = J 12d. EPE = 1/2kx^2 ; 1/2[(kg)(m/s^2)/m]m^2 cancels out to 1kg x 1 m/s^2 = J, the same way GPE = kx^2 does 13. EPE > KE > GPE > KE 14. During the push up of the ball is called work, that work is converted to kinetic, then to gravittional. 15. The baseball is initially at rest. It then is hit by the bat which does work which is made into kinetic energy until reaching the highest point, then it transforms into gravitational potential energy and the net and ground make the ball come into rest. 16. Soccer: the ball is moving at an increasing speed, with its kinetic energy, the ball is kicked up. this happens to the highest point and then kinetic energy transforms into gravitational energy.

What do you think now? 8
 * Its all about the speed and the upper body strength, if you are not going fast enough you will not reach the top of the ole.
 * Factors such as speed, the bending of the pole, the height of the person.

Chapter 2 Section 9
What Do You See? 9 I see an ice skater who is spinning in the air and getting a lot of hang time in the air.

What Do You Think? 9
 * Technically if you defy a law then you cannot be living because then that law would be a theory and not a law. I don't think it's possible for an athlete to defy the law of gravity. I don't know if it is possible for the skater to defy the law of gravity either.

Investigate 9 Figure Skater: 20 frames, 2/3 second Basketball player: 31 frames x 1/30 = 1 second

1. Stage one - bend knees ---> Normal Stage two - unbend knees drive hands up > (Normal force and weight) Stage three - off of floor (weight)(KE and GPE) 2a. We can conclude the force needed to jump a certain height. 2b. We will record the normal force (mass x gravity). 2c. We will use a scale and meter stick. 2d. We will analyze our date

3. Taylor's mass in kg = 79.38 kg Taylor's vertical height jump = 38 cm Taylor's hips straight up - 117 cm Taylor's hips bent - 86 cm  Taylor's hips in jump - 148 cm

Maurel's mass in kg = 65.77 kg Maurel's hips stright up - 99 cm Maurel's hips bent - 80 cm Maurel's hips in jump - 125 cm

4. Calculated force for Taylor: 2,010 N Taylor's Actual force: 1,909.89 N (Same equation as below to find force for me) W = GPE..... W = mgh. mg = 64.4kg (9.8). NF = 631.12N. GPE = mgh. GPE = 644.546 (.36). GPE = 232.03J... F x D = 232.03J. F(.15) = 227.2J... F = 1,514.67N Calculated force for Maurel: 1,502.64 Maurel's Actual force: 1,456.17 N Physics Talk 9 Conservation of Energy <jump chart in ready position about to jump, you have EPE from contractions in muscles. launch position has both GPE and KE energy of all positions of a jump are equal the greater the peak position, the greater the GPE trampoline potential energy from height jumping would provide kinetic energy when you land. when going down, you continue to have kinetic energy bc you would be losing GPE. The trampoline stretches & gains EPE at the expense of KE and changes in GPE example: all energy can be measured or calculated conservation on energy: total of all energies at any one time must equal the total of all energies at any other time collision between a player's foot and soccer ball, the ball can gain KE and move faster. Whatever the ball gained in energy, your foot lost that energy. No matter what is lost or gained, the total energy remains the same

Checking Up 9 1. The jumper can move from the ready position to the launch position from the contractions in the leg muscles (EPE) 2. in Launch position, the student has both GPE and KE. Peak of jump - GPE. 3. three other types of energy: light energy, chemical energy, sound energy

PTG 9 1. W = GPE W = mgh W = 50(9.8)1 W = 490 J 2. Bobsled run. W > KE > W 3. People would go about seeing if the statement is correct by making lines where the player's foot is during each frame. There they will see that the player does not actually hang in the air, but his maximum heights have little displacement therefore it results in people assuming that there is hang time. 4. If someone where to claim that a law of physics can be defied, they should give total proof of their information. Afterwards, someone else who is more knowledgeable and also has run many tests on the subject, can prove that the claim is not true. Therefore, both of them have the burden of proof. 5. An athlete can increase their jump by bending their knees more and swinging their arms more which both increase in electric potential energy and will increase KE and GPE. 6. W = F x d a) 1N x 1m = 1J b) 1N x 10m = 10J c) 10N x 1m = 10J d) .1N x 100m = 10J e) 100N x .1m = 10J 7. W = GPE a) 1N x 1m = 1J b) 1N x 10m = 10J c) 10N x 1m = 10J d) .1N x 100m = 10J e) 100N x .1m = 10J 8. KE = GPE a) 1N x 1m = 1J b) 1N x 10m = 10J c) 10N x 1m = 10J d) .1N x 100m = 10J e) 100N x .1m = 10J 9. W = F x d 50 x 43 2150 J 10. KE = 1/2mv^2 KE = 1/2(62)(8.2)^2 KE = 2084.4 J 11a. F = ma 6 m/s^2 11b. 563 J 12a. W = F xd 40000 = 3200 x d d = 12.5 m 12b. W = KE 40000 = 1/2mv^2 40000 = 1/2(1200)v^2 66.67 = v^2. 13. KE = W 1/2mv^2 = W 1/2(.15)(40)^2 = W W = 120 J 14. W = KE F x d = 1/2mv^2 417d = 1/2(64)(15)^2 d = 17.3 m 15-17. 18. In soccer, the ball is kicked described as work. Then it accelerates which is kinetic energy and is above ground which is gravitational potential energy. On the way down there is also kinetic and gravitational potential energy. At the end, there is friction to stop the ball, which is work

Physics Plus 9 1a. GPE = KE mgh = 1/2mv^2 (9.8)(20) = 1/2 v^2 196 = 1/2 v^2 392 = v^2 19.79 = v 1b. If it's mass independent, the amount of passengers on the roller coaster will not affect the ride. 2. EPE = KE 1/2kx^2 = 1/2mv^2 1/2(60)(.4)^2 = 1/2(.3)v^2 v = 5.66 m/s 3. GPEi+Win=KEf+GPEf+Wout mgh+F*d=1/2mv^2+mgh+F*d (200)(9.8)(25)+200,000=1/2(200)(40)^2+20(9.8)(h)+50,000 249,000=160,000+1960h+50,000 h=19.9m

What Do Think Now? 9
 * No athlete or person can "defy" the law of gravity and no matter what your body is going to be pulled down. The reason people are in the air longer is all about "hang time".
 * A figure skater does not "defy" the law of gravity either but the skater does get more height to stay in the air longer.