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=Chapter (2) Section (1)= toc http://www.howstuffworks.com/physics-of-football.htm My article talks about how physics plays into the sport of football. You use physics every time you throw the ball. The factors of the weight of the ball, how far away the receiver is, and the wind are all factors into how hard you should throw the ball. "We do not refer to this as physics because we do these simple calculations in our head.
 * Physics sport's current event**

There is a person running towards the goal and they kick the soccer ball so hard that it travels over the goal because they kicked it too hard. Then there is another kid that barely kicks the ball and it travels a few feet then falls right back down. The less force that is exerted into moving the ball the less the ball moves.
 * What do you see?**

1) Figure skaters are able to move across the ice so easily because the blades have such a fine tip so they do not create a large amount of friction and the ice is slippery so the blades slide easily across it. Once they have momentum they will keep moving across the ice. 2) The soccer ball continues to roll after you kick it because there is no opposite force acting on it and after you apply all that force to the ball to make it move it takes time to slow it down.
 * What do you think?**


 * Investigate**

Make a hypothesis. Answer the question to the best of your ability at this time. 

The higher the track is the faster the ball will roll causing it to gain more momentum.

Since I do not have the required equipment, we will use a simulation to conduct this experiment. Go to []. Launch the simulation. Be patient as it may take a few minutes to load and make changes.


 * 1) Set up the simulation and run the first trial.
 * 2) Press pause to stop the simulation. Note that the simulation ignores friction effects entirely.
 * 3) Check the box marked “Measuring Tape”.
 * 4) Use the default track and all other default settings. Use the measuring tape to measure the initial height. 
 * 5) Press Play.
 * 6) Place your cursor at the height point that the skater reaches on the opposite track. Measure the vertical height of this mark. 
 * 7) Change the position of the last blue circle to decrease the slope of the opposite track, but make sure that its end it still at least as high as the first blue circle.

>> The skater will keep going the same height because he keeps the same friction because they are both the same height and he starts from the same point. >> He starts at the same point and the slopes are still the same so he will go the same height. >> My prediction was very close because he kept going to the height each time. >> The skater starts at the same height each time and then travels the same height downward gaining the same momentum. The recovered vertical height is the same on each side because the height of each side is equal causing equal momentum of the skater. >> I predict that the skater will go higher on the side I lower because when he goes down the higher slope he gains more momentum causing him to go off the lower one. >> My prediction was correct in the fact that the skater went off the line that I lowered because it was too short. >> No because the line is horizontal and the ramp does not go back up in height. >> I think the skater would roll very far because he went down a hill causing momentum and staying straight slows him down very slowly. >> The momentum that he gained while traveling down the tall left side of the track. >> The skater goes down the track then travels for however long the track is and falls off because he still has momentum. >> It keeps the same length but it becomes more steep. >> The height it starts as is the same that is finishes as no matter of the slope. >> Both heights will be the same. >> Never the skater would keep traveling straight forever.
 * 1) Predict where the skater will reach his highest position if he begins at the same place as before. 
 * 1) Explain why you think so. 
 * 1) Press play. (Note: if at any time you need to zoom out, because you can’t see the end of your track, click the magnifying glass with the minus sign. The screen will adjust to fit your track.)
 * 2) How close was your prediction to the actual outcome? Why do you think your prediction was “close” or “way off”? 
 * 1) Measure the vertical height where the ball stopped. Write a sentence that fully describes the movement of the ball in terms of its starting and recovered vertical heights. 
 * 1) Repeat Steps 2 and 3, creating an even less steep slope.
 * 2) <span style="font-family: Arial,Helvetica,sans-serif;">First record your prediction. 
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Compare your prediction with the outcome. 
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Imagine what would happen if you changed the right-hand section of the track so that it would be horizontal (zero slope).
 * 2) <span style="font-family: Arial,Helvetica,sans-serif;">No matter how far along the horizontal track the skater rolls, would he ever recover his starting height? 
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">How far do you think the skater would roll? 
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">What would keep the skater rolling on a horizontal track? 
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Try this on the simulation. What happens? 
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Conclusion Questions:
 * 2) <span style="font-family: Arial,Helvetica,sans-serif;">What happens to the length of the opposite track the skater rides as the slope decreases? 
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">What happens to the final vertical position on the opposite track the skater rides as the slope decreases? 
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Remember that we are ignoring friction. The initial question was: “When a ball is released to roll down track and up the opposite side of the track, how does the vertical height that the ball reaches on the opposite side of the track relate to the vertical height from which the ball is released?” What is your answer to this question? 
 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">If the opposite track was infinitely long, and frictionless, when would the skater stop? 

Inertia is a property of matter that measures the resistance to change in an object's motion. Mass is how u measure an objects Inertia. Galileo Galilei was an italian philosopher who observed the first experiment that tested an objects momentum. He also realized that objects do not stop on their own but stop because there is a frictional force working Weight is how much gravity pulls on a mass. Mass is the amount of matter in an object or its tendency to resist a change in motion. Newton's First Law states that 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. Frame of reference is the prospective you have on an event.
 * Physics Talk**

1. Inertia is the property that measures the resistance to changes in an objects motion. 2.Newton's First Law states that 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. Friction stops it 4. The object with the greater mass. 5. Speed doesn't affect something inertia it all depends on mass. 6. Relative to yourself, the tree, or the ball.
 * Checking Up **

1) a) the ball will roll forever b) The object will remain in motion because newton's first law states that and object already in motion remains in motion with constant speed in a straight-line path. 2) It will reach 20 cm. 3) No because everywhere on earth there is friction. 4) Once the puck leaves the stick it will travel in a straight line but it will start to slow down a little because of friction. 5) The person standing sees the ball travel at 7 m/s because you combine both velocities. 4.5 + 2.5 = 7 m/s forward 6) 14.5 m/s because you add both velocity's together. 10.3+4.2= 14.5 m/s forward 7) a) 2.4+5.6=8 m/s forward b) 5.6-2.4=3.2 m/s forward c) you make a triangle and use pythagorean theorem. The net velocity = 6.1 m/s at 67 degrees. 8) 85 - 18 = 67 m/s forward 9) a) 15/sin45 = 21.2 cm b) 15/sin20 = 43.9 cm c) 15/sin15 = 58 cm d) 15/sin5 = 172 cm 10) 1. In curling when they launch the rock from its starting location towards the bullseye 2. In baseball when a pitcher throws a baseball from a standing position towards home plate. 3. When shooting a gun once the bullet is launched from the run and out the barrel it travels toward the target. b)1. Look at that nice throw by the curler right towards the center of the circle after using all their momentum to throw it. 2. And the pitch a fastball right down the center of the plate right into the catchers mitt. 3. That shot was a nice shot by the gunner across the grass and hitting the target right in the middle.
 * PTG**

- Figure skaters use momentum to gain speed on the ice and they continue gliding across because of Newton's first law where an object will stay in motion in a straight line. - The soccer ball is experiencing Newton's first law where an object once in motion will stay in motion is a straight line because of inertia.
 * What do you think now?**

2. In baseball players are not able to run through 2nd and 3rd base so they have to have a way to get their quickly but be able to stop on the plate. The result of this is sliding. Sliding causes a lot of friction between your body and the dirt on the ground. The more of your body you expose the faster you will slow down because of more friction. This allows runners to reach their top speed and then slow down quickly and stay on the base. http://www.redorbit.com/news/sports/1570114/the_physics_behind_baseball/
 * Inquiring Further**

See group page.
 * Reflecting...**

=Chapter (2) Section (2)=

There is a man on the top is extremely tired and walking slowly. The person on the bottom is sprinting with flowers to someone. The intervals between his feet are much larger than the man on top.
 * What do you see?**

Both numbers mean the same thing they are just different ways to express the same number in certain circumstances where one may work better.
 * What do you think?**

=Chapter (2) Section (3)=


 * What do you see?**

The man at first is moving very slow an the dog is able to keep up very easily. Then the person moves faster and so does the ball, also the dog is sprinting to keep up with the man. Lastly the man is sprinting and the ball is moving even faster. The dog has to drive in a car to keep up with the man.


 * What do you think?**

A force is a push or a pull on an object that can make it some in a certain direction. The force acting on both objects would be the same however the bowling ball would have less action because it has more mass.


 * Physics Talk-**

This physics talk is all about Newton's second law and how if there is acceleration on an abject then there must be an unbalanced force causing that acceleration. Gravity can be a force also and the force of gravity(9.8 m/s^2) is the weight. If an unbalanced force acts upon an object there will be acceleration unless the forces are the same in opposite directions which can cause the net force to be 0. Mass does not matter what gravity is however the weight of an object depends on gravity.


 * Checking Up-**

1. Newton's second law states that there can not be acceleration without an unbalanced force acting upon the object. The acceleration depends on how strong the force is and the mass of the object. 2. If you increase the mass of an object which using the same amount of force the acceleration will decrease because it makes it harder to move the object. 3. Newtons relates to weight so if an object weighs 30 newtons than that is the gravity multiplied by the mass of the object. 4. If you were on a planet with higher acceleration than you would weigh less than you would on earth even though your mass would be the same. This means the unbalanced force would be less to move you the same amount on earth.


 * PTG**

1a. 70kg x 5m/s = 350N 1b. 800N / 10m/s = 80 kg 1c. 70N / 7kg = 10m/s 1d. 400 N / 5m/s = 80kg 1e. -1500N / 100kg = -15m/s 1f. 100kg x -30m/s = -3000N 3. A = F/M A=42 n/ .30 kg = 140 m/s^2 4. A = F/M 20= F/ 0.040 F= .8 N 5a. Most people would rather catch a baseball rather than a bowling ball because of its much less mass. Because of the greater force and mass of the bowling ball it would be a lost harder to stop. This can be related to Newton's first law of motion. 5b. A baseball will have greater acceleration than a bowling bowl if you excerpt the same amount of force on both because the mass of the baseball is much less than the mass of the bowling ball. This is related to Newton's second law of motion. 9. When throwing a baseball it will travel in a straight line forwards until an unbalanced force acts upon it being the person mit catching the ball. 10. The unbalanced force is sarah pushing on it plus the other force. The sum of these two force is the net force which is 90N. 11. 200N x 4 people = 800N total because each person exerts 200N of force. 12. A= F/M A= 125/.7 = 179 m/s^2 13. pythagorean theorem = a^2+b^2=c^2 50^2+120^=c^2 c= 130 @ 67 degrees NE 14. pythagorean theorem = a^2+b^2=c^2 4000^2+5000^2=c^2 c= 6403N @ 53 degrees NE 15. F= am F = (12.8)(9.8) F = 125N 16a. pythagorean theorem = a^2+b^2=c^2 30^2+40^2=c^2 c= 50N at 53 degrees 16b. A = F/M A= 10/5.6 A= 1.8 m/^2 17a. pythagorean theorem = a^2+b^2=c^2 30^2+20^2=c2 c=36N at 34 degrees 17b. A= F/M A = 34/100 A = .36 m/s^2 17c. If both were to the left the total would be 50N. A= F/M A= 50/100 A= .5 m/s^2 18. In baseball pitchers can throw the ball up to 100MPH. The ball only weighs .2kg. The batter hits the ball with other 500N of force sending the ball into the outfield eld and into a fans mitwhere the ball comes to a complete stop!


 * Physics Plus**

1. 125N north and 125N west a^2+b^2=c^2 125^2+125^2=c^2 c=176.8N 2a. Player A 40N n Player B 70N s 70-40= 30N s because 70 is more than 40 and the 40 cancels. 2b. All players forces - a^2+b^2=c^2 30^2+40^2=c^2 c=50N 2c. Southwest because there is force south and west.


 * What do you think now?**

A force is measured in newtons and it is something that is applied to an object causing motion. To find force you need to know the acceleration and mass of the object. The greater the mass the more the force because they are directly related. Mass and acceleration and indirectly related because the more and objects mass the slower it will accelerate. The difference between a tennis ball and a bowling ball is a tennis balls mass is much less so the same force applied to both will move the tennis ball more.

=Chapter (2) Section (4)=

A lady is letting two apples fall to the ground on each side of a man. They are even horizontally and they both hit the ground at the same time. However one apple goes straight down and one goes on an angle outward.
 * What do you see?**

There are a few factors that determine how far an object will go. One is the objects mass because the lighter the object the easier it is to throw it further. Also the force you put in to throwing the object determines how far it goes. Some objects of some shapes make it aerodynamic so they go through the air easier.
 * What do you think?**


 * Physics Talk**

A trajectory is a path in which an object moves. Projectile is an object acted upon only by gravity. The x-component and y-component of all vectors are independent. 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. Mass is irrelevant gravity is what causes objects to fall at the same speed.

(Part A+B on group wiki)
 * Investigate**


 * Checking Up**

1. If you dropped a pen and a ruler at the same time at the same height they would hit the ground at the same time because they have the same force of gravity pushing down on them. 2. If an object falls straight down on its vertical axis it wont remain the same because vertical velocity always changes. 3. If you throw a ball in the air the highest velocity it reaches is 0 and the acceleration is -9.8m/s^2


 * PTG**

1 & 2- 4. Everyone thought that the bullet being shot would hit the ground first. When asked why most people said that the force pushing the bullet out of the gun would keep it in the air longer then the one simply being dropped. The reason they would both hit the ground and the same time is that they both have the same gravity pushing down on them. 6. Horizontal motion has no affect on vertical motion because it takes time for a horizontally launched projectile to hit the ground while in the air. Things like gravity only affect the vertical motion. 7. A and B will hit the ground at the same time. They are both dropped or shot from the same height and the bow is being shot horizontally. 8. 3.6 @ 33.7 degrees 9a. 11.98m/s 9b. 23.96 m 10a. 8.5m/s 10b. 4.25m (work below)

11) Well after that stop on 3rd down it brings out a long 4th and 20 for the hills football team. The punter comes on and boots the ball as hard as he can wow look at that ball fly. The punter put the perfect amount of arc on the ball and really kicked it quite far. The gravity of -9.8m/s^2 pushing down on this ball is really going to make it hard for the punt returner to catch this ball.

http://www.youtube.com/watch?v=SDbRpJvvy0Q This video tells the different factors that come into punting a football. 1. The first main tip is to kick the ball at an angle and not horizontally. The bigger the angle of your kick, the higher your ball will go which causes more hang time. The football loses speed as it reaches the max height but once it gets there and begins its descent down it gains speed because of gravity acting on it.
 * Physics Clip**
 * 2. The trajectory of the football plays a huge part in how far it goes. To reach max distance the angle should not be to high or to low. In the clip the punter gets a perfect angle combined with a high force from his leg which causes the football to travel the greatest distance. **


 * Active Physics Plus**




 * What Do You Think Now?**

To know how far a projectile will travel during flight you need to know some variables and measure the launch velocity and initial height of the projectile. When you change the launch velocity positively than the range will increase as well as if you change the initial height. This relationship between your launch velocity and your initial height can help you determine other factors of your launch.

=Chapter (2) Section (5)=

There is a soccer ball is being kicked up in the air at a very big angle, Because this angle is so big, the ball isn't traveling very far but it is going very high. A little boy then heads the ball at a smaller angle less then 45 degrees. The ball is traveling a lot farther but not going as high up. the picture shows the trajectory of the ball.
 * What do you see?**

1. smaller angles have long ranges velocities and are up for a shorter amount of time larger angles have smaller rangers and are up for longer amount of time 2. The greater the speed, the faster the object will travel, so the range will be longer.
 * What do you think?**

Projectiles have two different types of motion that act at the same time, having no affect on one another. One of them is constant along a straight line, and its affected by launch speed and direction. The other is downward acceleration, which is a constant of -9.8m/s^2. This is affected by launch. The math model has a table of times, distances, and speeds during the fall. The physical model is the even spaced strings of calculated lengths. All projectiles are parabolas (omitting air resistance.) A 45 degree launch produces the greatest range, or the largest distance covered. Small angles have greater horizontal velocities, but less hang time. Larger angles have greater hang time and less horizontal velocity.
 * Physics Talk **

1. Constant motion and acceleration help you understand the trajectory of a projectile. 2. For a model to be accepted, it must match reality in nature 3. Height and range with different angles; 45 degree launch produces the greatest range. When pairs of angles add up to 90 degrees, distances will become identical. When going from 10 to 80, horizontal velocity increases and vertical decreases.
 * Checking Up**


 * Physics Plus**


 * PTG**

1. 45 degrees because the object will go the farthest it can. 2a. When bigger than 45 degree angle, the less far the object will go, the more time you will spend in the air. 2b. As the angle gets bigger before it hits 45 degrees, the object will go farther, but the smaller the angle, the less amount of time in the air. 3a. 90 degrees- 30 degrees = 60 degrees 3b. 90 degrees- 15 degrees= 75 degrees 4.) I think this occurs because most people can run faster than they can jump high. If she runs really fast before hand, she will have a bigger range without jumping at a 45 degree angle. 5.) I think that he was successful in his events because if he goes his highest velocity. He has a great horizontal velocity when he is running before hand and he is also good at launching himself upward at a fast speed. 6a.) The balls acceleration is -9.8 m/s squared. 6b.) The direction of the balls velocity at point x is downward. 7a.) V= Vi +at (-9.8) (3) = 29.4 m/s Speed = 29.4 m/s 7b. horizontal speed after 1 second: 5m/s 7c. 15m from the cliff 8. 45 degrees creates the longest range 9. The angle closest to 90 degrees creates produces the greatest projectile height 10a. direction of acceleration: east 10b. d=vit+.5at^2; -100=-4.9t^2; t=4.5 seconds 10c. 90m from the cliff d=vit+.5at^2; d=20(4.5) + .5(0)(4.5)^2

A 45 degree angle gives the longest range. Anything bigger gives you more time in the air but a shorter range. Any two complementary angles (add up to 90) give you the same range. With 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.
 * What Do You Think Now?**

=Chapter (2) Section (6)=

I see a person on a chair with wheels with his feet on the wall. He pushes off the wall and flies back fast with the chair on the floor and his body still in the chair.
 * What do you see?**

To jump the highest you can, I would suggest bending your knees as much as possible and pushing off the ground the hardest you can. Apply force to the ground.
 * What Do You Think?**

This talk is all about 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.
 * Physics Talk**

1. Newton's 3rd law of motion is, if you push or pull on something, it will push/pull back with equal force in the opposite direction. Forces come in pairs and act on different objects. 2. The mass pulls up on the force with an equal force of gravity. 3. A free body diagram illustrates the forces acting on an object. Arrows represent the type of force and the direction of this force.
 * Checking up Questions**

1. Yes because for every reaction there is an opposite equal reaction. 2. No because restoring forces balance downward weight. Restoring force is equal to the force your putting down. If the material is too weak, than it will break. If the material can't withstand the force, it will break. 3. The bathroom scale is a spring with a needle attached, and then calibrated. It measures weight and force through the equation of mass times gravity. It measures the mass of the body exerting a force on the scale and multiplies it by 9.8. 4. The forces on each other are the same. Break because the fastball is too big for the material to withstand. 5. When large players in football exert all their momentum into small running backs they may not be exerting the sam amount of force on each other. However the mass of the larger player is larger and the acceleration of the smaller player is bigger and they are moving towards each other. 6. The force of the boards on the player is equal to negative the force a player has on the boards. 7. Baseball players use gloves in baseball because if they were to just use their hands than they would have to apply the same amount as the baseball to stop it. The glove also pads the players hand to protect it from that large force of the ball. 8a. Both skaters are quickly racing down the ice for the puck while not looking up. They have the same mass and are traveling at the same acceleration. BAM they slammed into each other causing both of them to fall backwards and on their butts. 8b. A deflection of the ground can produce a force, if you fell. If you fell, you would be pulling up the force from the ground while pushing down the force of your own. This can be made funny and comical if a major wipeout were to be shown with comical commentary.
 * PTG**

When jumping in the air, you are applying a gravitational force downward and a normal force goes through the body upward towards the sky and off the ground. We push down on the floor with force to go up. Newton's third law explains that every force and an equal but opposite force, so therefore, the floor shares this relationship with the person jumping.
 * What Do You Think Now?**

=Chapter (2) Section (7)=

The man is trying to pull the shoe on the ice and it is very easy because there is barely any friction on ice. However he is struggling to pull the shoe along the desert ground because of the high amount of friction.
 * What do you see?**

Some sports require different shoes because of the different surfaces they are played on. These different shoes are useful because they can give a person grip on the surface so they have the best ability to move.
 * What do you think?**


 * Physics Talk-** Friction is defined to be the force that resists relative motion between two bodies in contact. There was a second force on the shoe of equal strength and in the opposite direction when we pulled it. This was the force due to friction between the shoe and surface. The pulling force was equal to the frictional force, and the net force was 0. A normal force is defined to be the force acting perpendicularly or at right angles to a surface. Coefficient of a sliding force is a dimensionless quantity symbolized by mu. Mu=force of friction/normal force. The force of friction is equal to the force required to slide the object at constant speed across a surface.

1. The force of friction is equal to the force read on a spring scale because the force of pulling that was applied to move the shoe was equal to the frictional force. They were in opposite directions, making the net force equal to zero. 2. The coefficient of friction has no units because its a force divide by another force 3. The force of friction is equal to the force required to slide the object
 * Checking Up Questions**

1. Running, an outdoor sport, can be a dangerous sport depending on weather conditions and the running shoes one wears. It is very important to have correct shoes to prevent injury. If running on a wet surface due to rain, the person may want to wear shoes with little spikes that can gain traction on the track, in order to prevent a bad slip. Running shoes are very light, and if the shoe were to be a little heavier, it may be more safe because the shoe can have thicker treads. 2. Ice skating is a sport which requires minimal friction. The skater wants to have clean, sharp blades every time when entering the ice. If the blade is chipped and not well groomed, the skater may fall, and not glide smoothly on the ice. To reduce this friction, skaters clean their skates before and after going onto the ice. 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. 4. Tennis players have different shoes for clay, grass, and hand surfaces. For the hard surfaces, their shoes need to provide more friction. On the clay courts, which are more slippery, the shoes need to provide more friction & have a good grip. For grass, the shoes need to provide less friction. 5. The minimal horizontal force would be 18 newtons. µ=f/N (.03=__/600)=18 6a. w=mg w= (1000)(9.8) w= 9,800N 6b. µ=f/N .55=f/9,800 f=5,390 N 6c. Fx=MAx f=ma -5390=1000a a=-5.39m/s^2 6d. Vf=Vi+at 0=Vi+(-5.39)(6) Vi= 32.34 m/s, change in speed 6e. The original speed was 32.34 m/s. The claim was wrong because he was going faster than he said (29m/s). He had to stop short because he was going faster, causing his stop to be more dangerous and sudden. His decreasing acceleration was -5.39 and it took 6 seconds for him to come to rest. 7. As you are going faster and faster, there is more and more air resistance. If you try to run through the water, it gets harder and harder to do. The resistance picks up as the speed picks up. When I am running and increasing speed, the same wind resistance is hitting my face. Air and water resistance depend on speed. 8. If there is a max. force it will set a limit on how fast you can start. Even if you have incredibly strong legs, it won't have more acceleration. To solve this problem, we can reduce friction by buying shoes that have a smoother surfaces. fkMax limits acceleration 10. Without friction, one can not walk. Friction is important to running because you need to have traction in the ground to for safety so one will not slip and keep their footing. In baseball, football, and soccer, cleats are used because you need friction and spikes to keep footing in different surfaces that may not give you with flat-bottomed sneakers. 11. The football is received by the kick returner and his new cleats with extra spikes on the bottom for increased friction with the grass. Watch him as he is able to juke out all the defenders on his way to the end zone to score the winning touchdown. None of the defenders were able to make the cuts and turns he was able to without falling due to their faulty cleats.
 * PTG**


 * Physics Plus **

The force of friction is equal to the force required to slide with constant speed (sometimes tension). Different sports require different, but special shoes because of certain weather conditions and field conditions. Indoor sports like basketball need shoes with good traction so they can keep footing. Also, for tennis, you need proper sneakers to keep footing on the hard surface. But, if you are playing on a slippery and muddy grass field, you would want to wear cleats with spikes to gain traction and a good grasp of the ground. This cleat is smooth and lighter so it can accelerate better in worse conditions, so there wouldn't be a large mu.
 * What do you think now? **

= Chapter (2) Section (8) =

There is some horizontal speed to accelerate and are trying to transform into a vertical acceleration. The pole bends, and there is some flexible force that will help them pole vault to the top of the roof.
 * What do you see?**

The vaulter may not be able to go over a 12.0 m high bar with a 11.0 m long pole because they can't accelerate quick enough and go with a constantly increasing momentum that the pole would bring them over the high bar. Factors that limit height of pole vaulter: acceleration, velocity, length of pole, momentum, distance
 * What do you think?**

a. We will hold it on the opposite side of the ruler, and there is a line on the ruler that stops the penny. We will hold the ruler pretty far off the ledge. We don't want it to be that flexible. b. The bend of the ruler (deflection) which represents the force you use, elasticity of the material, length of the ruler, placement of the object on the ruler, mass of the object
 * Investigate-**

a. how the penny changes when it amount of ruler sticking out changes. b. the height of the penny when the distance changes. c. meter stick, ruler, penny, table, tape d. by keeping track of the height of the penny when the rulers position changes.
 * Lab-**

When a force acts on an object, the speed and position may change. Kinetic energy is associated with motion and gravitational potential energy is associated with position. When forces act on objects, energy changes from one form to another. The sum of the kinetic and potential energy remain constant. Work is the product of the displacement and the force in the direction of the displacement. The law of conservation of energy states that matter (energy) can neither be created nor destroyed. All energy units are in Joules (J).
 * Physics Talk**

1. A force is required in order for the energy of an object to change. 2. In the investigation, the penny gains its energy from the force that is put on the ruler, then pushing against the penny. 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 energy as the pole bends. 4. Joules are used for all energy problems.
 * Checking Up**

Speed is the changing component to this situation. A person's height can not just increase that shortly. If speed is increased, distance will as well. Also, the pole is not able to just increase in size because it has to be a standard height. The higher initial velocity, the more kinetic energy involved, which then transfers to a high elastic potential energy, which will then lead to the gravitational potential energy, making the competitor gain a good height. = = = Chapter (2) Section (9) =
 * What Do You Think Now?**

An ice skater is spinning in the air. He seems to be floating in the air while the helicopter keeps track of the guys hang time.
 * What Do You See?**


 * What Do You Think?**


 * Investigate**


 * Physics Talk**


 * Checking Up**