NHoogland+Physics+in+Action+Chapter+2

= = toc Chapter 2

Section 1
Sports Article 11/7/10 This article is about the physics in soccer. This is because of all the forces that go into the soccer ball when it is kicked and moving. http://www.soccerballworld.com/Physics.htm

What Do You Think? 11/8/10 Figure skaters keep moving across the ice at high speeds for long times while seeming at no effort by pushing off their legs it gives them movement for them to glide across the ice. A soccer ball continues to roll across the field after it has been kicked because of the force that kicked it was so strong that it keeps going. For both of these cases the person adn the soccer ball will continue to move unless and unbalanced force act upon it.

Investigate 11/8/10 a) Press pause to stop the simulation. Note that the simulation ignores friction effects entirely. b) Check the box marked “Measuring Tape”. c) Use the default track and all other default settings. Use the measuring tape to measure the initial height. **5.03** d) Press Play. e) Place your cursor at the height point that the skater reaches on the opposite track. Measure the vertical height of this mark. **5.03**
 * 1) Set up the simulation and run the first trial.

2. a) Predict where the skater will reach his highest position if he begins at the same place as before. **It will be even to where his beginning was.** b) Explain why you think so. **This is because It will have the same slope and be going the same distance.** 3. 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.)

a) How close was your prediction to the actual outcome? Why do you think your prediction was “close” or “way off”? **My prediction was close because I used common sense that the height will be the same in the ending as when he started.** b) 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. **The starting and final heights that he is going is the same, which is 5.03**.

4. Repeat Steps 2 and 3, creating an even less steep slope.

a) First record your prediction. **I predict that the final height will be lower with a less steep slo**pe. b) Compare your prediction with the outcome. **My prediction was right, but it was not lower by a lot. If you continue too make it too low, then the skater will fall off.**

5. Imagine what would happen if you changed the right-hand section of the track so that it would be horizontal (zero slope). a) No matter how far along the horizontal track the skater rolls, would he ever recover his starting height? **No he won't because he is flat and it won't ever go back to the steepness.** b) How far do you think the skater would roll? **He will roll until he falls off the ramp.** c) What would keep the skater rolling on a horizontal track? **The push that he starts off with.** d) Try this on the simulation. What happens? **He stopped at the same height that he started at.**

6. Conclusion Questions: a) What happens to the length of the opposite track the skater rides as the slope decreases? **The length becomes more horizontal.** b) What happens to the final vertical position on the opposite track the skater rides as the slope decreases? **It becomes more even with the starting position and has a lesser slope.** c) 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? **The height of the starting and final position is the same.** d) If the opposite track was infinitely long, and frictionless, when would the skater stop? **No, the skater would keep on going unless and unbalanced force interfered.**

Physics Talk Summary 11/8/10 Galileo was the one to conclude that a ball will continue its motion on the horizontal surface with constant speed along a straight line "to the horizon". This shows that an object at rest remains at rest unless something causes it to move, Galilkeo formed the law of inertia. Inertia is the natural tendency of an object to remain at rest or to remain moving with constant speed in a straight line. Property of matter that resists changes in motion. Moving objects might continue to move forever unless a force, a push or a pull, stopeed them. Newton's first law of motion was 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. He also explained that mass is a measure of its inertia, or tendency to resist a change in motion. The speed of an object is the sum of each of the above speeds. Velocity is speed in a giant direction. A change in speed during a specific time is referred to as acceleration. Acceleration occurs during starting, stopping, and changing direction. measured-->mass. units-->kilograms. Frames of reference and running start increase distance and/or speed to give advantage. Frames of reference "releative to" adding or subtracting velocities.

Checking Up Questions 11/8/10 1. Inertia is the natural tendency of an object to remain at rest or to remain moving with constant speed in a straight line. 2. Newtons first law of motion was the absence of an unbalanced force, an object remains at rest, and an object already in motion remains in motion with constant speed in a straight-line path. 3. An external force needs to act on an object to stop it from moving at a constant speed. 4. An unbalanced force stops the motion of the ball. 5. The greater size mass will have the greater inertia. 6. It is important to establish the frame of reference when describing the speed of the ball because you could get both values and they could both be correct it just depends on the frame of reference.

Physics To Go 11/9/10 1a) The ball will continue to roll forever. b) This is correct according the Newton's first law of motion which states an object at rest remains at rest, and an object already in motion remains in motion with constant speed in a straight-line path. 2. It will reach 20 cm. 3. No, because it is not realistic to believe that an unbalanced force will never act upon the object. It is impossible to have a frictionless world unless it is in space. 4. Once the hockey stick hit the puck the puck will keep on going until an unbalance force acts upon it because the force of the hockey still is so strong. When an unbalanced force does act upon the puck, it will bounce off of whatever that is because the hit was so strong. There's not that much friction on ice. 10a) Soccer, when the ball is not hit it will stay at rest. When someone kicked the ball than it will continue to move. Golf, when the goldball is not hit it will stay at rest. When the golfer hits it, it will continue to go in the motion. Ice skating, when the skater stays still they will stay at rest, when the skater has a running start they will continue in motion. b) "That kick was so strong that the ball is going to go until someone stops it!". "The golfer now hit the ball, let's see how cloe it get to the hole!". "The skater has now starter her first move, and will stop when she is done with her routine!". What Do You Think Now? 11/10/10 ﻿Figure skaters keep moving across the ice at high speeds for long times while seeming to expend no effort because of Newton's first law of motion, and ice how very little friction. A soccer ball continues to roll the field after it has been kicked because the ball will continue to move until an unbalanced force acts upon it. The hit that hit them to start moving is what is keeping ti going and it keeps moving because nothing interferes with it that would stop it. Inquiring Further 11/10/10 2. You slide into second and third base because when you get to the base quicker because when you slide your momentum stays the same and when you run you have to slow down because you cannot overshoot second and third base. You do not slide into first base because you can run over first base and not be out. http://answers.yahoo.com/question/index?qid=20090823160105AA4GAAd
 * 5-9

Section 2
What Do You Think? 11/10/10 100 mi/h means that you are going 100 miles in one hour. 45 m/s means that you are going meters per second. These are difference units for both things, so you cannot compare them and say which one is faster or slower unless doing some sort of calculation and converting one into another. Physics Talk 11/11/10 At a fast, constant speed, you cover a greater difference during a given time interval than when you travel at a slow, constant speed. One way to measure motion is so calculate speed. The unit for speed is always written as distance per unit of time. Average speed is the distance traveled divided by the time taken to travel that distance. Instantaneous speed is the speed at the moment. When an object is changing speed, it is accelerating. Acceleration is the change of speed divided by time. Acceleration is also the change in the direction of motion. To calculate acceleration in one direction caused by speeding up or slowing down, you divide the change in speed by the time interval during which the change took place. Checking Up Questions 11/11/10 ﻿1a) The dots are evenly spaced.  b) The dots are far apart. c) The dots are close together. 2) 400/50= 8. The runners average speed is 8 m/s. 3) Instantaneous speed is speed at the moment and average speed is the average of the distance and time that you have traveled. 4) 11/10=10. The average acceleration is 10 km/h. Physics To Go 11/12/10 1) Average speed is the average of all your speed throughout your whole trip, and instantaneous speed is the speed you are going at the moment. 2a) 1/15= .06 repeating km/s b) 84/6= 14 m/s c) 9.6/2= 4.8 km/h d) 400/4.5= 88.8 repeating km/h 3a) Acceleration is negative. b) Acceleration is positive. c) There is no acceleration. d) Acceleration is negative. e) There is no acceleration. f) There is no acceleration. 4a) A and D b) B c) A d) C e) a is positive, b is none, c is positive then negative, d is positive. 6. a) v/t 45 km/h / 9 s--> 1000 mx3600/9 5 km/s---> -1.4 ms/ squared b) negative value 7a) Constant b) Positive acceleration c) Slow, fast, faster d) Slow, constant, fast 8. av = d/t 100 mi / 2 h 50 mph 9. No, they could have stopped and gone slower or accelerated to a faster speed. That is just an approximate speed they travelled. 10. The dots on the ticker tape are going to farther apart as she accelerates to her top speed. 11.a = v/t 4 m/s =v 5 m/s 20 m/s 4,8,12,16,20 m/s 14a) Runner b) Racecar c) Walking d) Runner in the beginning of a race e) Jumping on a trampoline, when you're stopping What Do You Think Now 11/15/10  ﻿ 100 mi/h means that you are going 100 miles in one hour. 45 m/s means that you are going meters per second. These are difference units for both things, so you cannot compare them and say which one is faster or slower unless doing some sort of calculation and converting one into another. I would now explain it by doing average speed is the average speed you are going at a distance in an elapsed time. Physics Plus  11/16/10

Section 3
What Do You Think? 11/16/10 A force is the push behind the ball that allows the ball to move fast. A force behind a tennis ball does not have to be as strong because the ball is lighter and has less weight. The force given to a bowling ball has to be greater because the ball is heavier. Physics Talk 11/16/10 Newton's second law can be written as an equation: acceleration=force/mass. a=f/m. Force is expressed in newtons and mass is expressed in kilograms. You measured speed in meters per second and acceleration in meters per second per second, or meters per second squared. In Newton's second law force is expressed in newtons. A newton is derived SI unit with a special name. Newton's second law tells you that accelerations are caused by unbalanced forces. When you apply a force to an object that has a small mass, the accelereration will be smaller for the same force. Occasionally, the mass is so large that you cannot measure the acceleration because it is so small. Weight is the force of gravity acting on an object, and it depends on the mass of the object and the acceleration due to gravity. f=ma. w=mg. When two forces act at the same time, the direction as well as the magnitude of the forces determine the motion of the option. If the forces are in the same direction, then the sum of the forces or net force will cause a larger acceleration than either force alone. If two forces are in opposite directions, then the net force could be zero and there would be zero acceleration. A free-body diagram is a diagram used to show the relative size and direction of all forces acting on an object. Sometimes when the force you apply is immediately balanced by a frictional force or force of air resistance so that there is no acceleration. Checking Up Questions 11/16/10 ﻿1. Newton's second law of motion states that accelerations are caused by unbalanced forces. 2. The effect is the larger the mass, the less the force will be. If the mass is less thn the force will be great and the object will move fairly far. Physics To Go 11/18/10 1) 350 N 80 kg  10 m/s^2  80 kg  -15 m/s^2  -3000 N 3) a = F/m=42 N/.30 kg=140 m/s2 4) F = m x a= .040 kg(20.0 m/s2)= .8N 5) a) An object will stay in motion until it is stopped. If a bowling ball was given enough force and is coming toward your face, it is going to be very difficult to stop because of its mass. The bowling ball won't travel as far because of its weight. The baseball will be easier and go farther because it is light.  b)The acceleration of the bowling ball will be less than the acceleration of the baseball. 9) Yes, it is because that was the force that is causing the ball to accelerate. It is the way that the ball started moving. It will stop when the object is stopped. 10) 50N+40N=90N 11) 800 N 12) a=f/m=125N/700g=.18 m/s^2..wrong. right-**179 m/s^2** 15) F=m(a)=(12.8 kg) (9.8 m/s^2)=125.44N 18) Acceleration and force both depend on the weight of an object. The more force you put into an object with a small mass, the bigger the acceleration will be. Putting in the same about of force on a larger object, the acceleration will be a lot slower. 14 wrong- 6403N and 39 degrees. 16 wrong- 50 N and 53 degrees. B- 8.9 degrees 17 a- 36 N at 34 b- .36 m/s^2 c- .5 m/s^2
 * 3. The object's force is 30 N. Its mass and its acceleration has to equal 30. **
 * 4. My weight would stay the same but my mass would decrease because of the the lower gravity. **

What Do You Think Now 11/19/10 Force is a push or pull on an object that causes acceleration to occur. If you put a lot of force into a tennis ball then the acceleration will be larger. If you put the same amount of force into a bowling ball, then the object will have less of an acceleration because the mass is so great. Physics Plus 11/22/10

Section 4
What Do You Think? 11/23/10 ﻿What determines how far an object thrown in the air travels before landing depends on the mass of the object and how it is thrown. As well as the velocity and speed of the object.

Investigate 11/23/10 ﻿1) They do hit the floor at the same time.  2) They hit the floor at the same time. 3a) No, the speed of the projected coin does not affect whether the two coins hit the floor at the same time. b) Yes, if it is dropped horizontally instead of straight down it will go out farther. c) 4. The coins hit the floor at the same time. The height does affect how far the coin goes while it is horizontal. 5. I think that the ball will move with the person in the chair. 6a) The ball goes with the person in the chair that is throwing it. b) How the person throws it, how fast they're moving, and if they are remaining at constant speed.

Physics Talk Summary 11/23/10 ﻿It is always true that a horizontally thrown coin and a dropped coin hit the ground at the same time. The horizontal motion of the coin does not affect its downward motion. A projected coin has a constant speed to the right, when there is no air resistance. Any hit or thrown ball travels horizontally or vertically. The horizontal velocity remains the same. The vertical velocity is constantly changing. Projectile- the only force is weight. Launched through the air. Ignore air resistance. Trajectory- Path of projectile. Ground-to-ground are symmetrical around highest point. x and y information are independent. Ay=-9.8 m/s^2, Ax=0. If these aren't true, it's not projectile. Freefall is the only force is weight but it's 1 dimmensional motion (only vertical). Vertical positions of freefall and projectile are same.

Checking Up Questions 11/23/10 1. Yes because if there is no acceleration then gravity acts on both the same way. 2. No, because it speeds up. 3. The velocity and the top will be 0, and the velocity going down will be -9.8.

Physics To Go 11/23/10 1)  2)   ﻿4) I surveyed three people. All of them thought that the bullet that is dropeed will reach the ground first. None of them said the one shot horizontally would reach the ground first or they would hit the ground at the same time.  6) If it is shot horizontally it would not affect the motion on the object. If the person was moving too fast than the ball would go behind the chair but if the person stopped the ball would go ahead of him. 7) A and B will hit the ground at the same time because they're both shot and dropped at he same height and the bow is being shot horizontally. 8&9) 9a) 11.3 m/s b) v=d/t 11.3=d/2 d= 22.6 m 10a) 12 m/s b) 4.25 m 11) THe first pitched was pitched horizontally at a speed of 40 m/s. The batters hit goes in the outfield at an angle of 37 degree. The ball then drops and the velocity gets higher as it falls.

Physics Plus 11/20/10

What Do You Think Now? The balls distance that is thrown depends on the speed that it is thrown as well as the angle that it is thrown at. Before 45 degrees, it will go far, after 45 degrees, it will not go very far. The higher the speed, the farther it will go.

**Section 5**

What Do You Think? As the angle gets bigger, the ball with go farther, up to 45 degrees. The object will go the farthest it can at the same speed. After 45 degrees, the ball with started to go less of a distance each time. Complementary angles have the same range for a ground to ground launch. If an object is launched at the same angle, the higher the launch speed is, the farther it will go. Physics Talk Summary 12/1/10 ﻿The main thing that scientists do is create models to help understand how things in nature work. A mathematical model is the table of times, speeds, and distances during falling. Physical model is the table of evenly spaced strings of calculated lengths. Trajectories of projectiles can be modeled using a computer or graphing calculator. This allows us to manipulate variables such as launch angle, launch speed, launch height, and range to enhance your ability to simulate, explore, and understand projectile motion. For ground-to-ground complementary angles have the same range. 45 degree has greatest range. Checking Up Questions 12/1/10 ﻿1) Constant speed and downward acceleration.  2) Create models to help how things in nature work. 3) Because small angles have greater horizontal velocities but are in the airy a short time. Large angles have smaller horizontal velocities but are in the air a long time. Physics To Go  12/2/10 1) 45 degrees because the object will go as far as it can. 2a) If the angle is bigger than 45 degrees, how much bigger it is the farthest the object will go. b) When the angle gets bigger before it hits 45 degrees, the object will go farther. 3a) 90-30=60 degrees. b) 90-15=75 degrees 4) I think this happens because most people can run faster than they can jump. If she runs really fast beforehand, she will have a bigger range without jumping at a 45 degree angle. 5) I think that he was successful if he goes his highest velocity. He has a great horizontal velocity when he is running beforehand and he is also good at launching himself upward at a fast speed. 6a) The balls acceleration is -9.8 m/s squared. b) The direction of the balls velocity at point X is downward. 7a) v=vi+at= -9.8(3)= 29.4 m/s b) 15=Vi(1)= 5 m/s c) d=vit. d= 15 m 8) The angle would have to be 45 degree to travel the farthest distance. 9) The biggest angle would be close to 90. 10a) The acceleration is downward, -9.8 m/s^2 b) d=vit+1/2at^2= -100=-4.9t^2 t= 4.5 seconds c) d=vit+1/2at^2 d=20 (4.5) d= 90 m

Section 6
What Do You Think? 11/11/10 ﻿You should apply your forces down by bending your knees, then force yourself to go up by pushing yourself form your knees off the ground and then go down on your feet. Physics Talk Summary 11/13/10 When two people push on each other they both accelerate backwards because of the force of the other person. When you are walking, the force you add to the ground is the same that the ground adds to you. The forces are opposite in direction, making you accelerate forward. Newtons 3rd law states that for every force, there is an opposite and equal force acting back. They always act on different objects.A free body diagram lets you see what forces are acting on an object. Forces are represented by arrows, and the size represents how much force. You are held down by your mass. Newton first wrote his law in the book Principa. Because of things like traction and friction, this law doesn't always apply. Situations like person pulling a chair on wheels doesn't apply because the forces aren't equal. There are two forces acting on the person and one on the chair which is why it doesn't fit Newton's law. Checking Up Questions 11/13/10 1) Newtons third law says that for every actions, there is an equal but opposite reaction. 2) A normal force is the opposite force. 3) A free body diagram shows all the forces and how they are acting on an object. The forces are represented by arrows, and the longer they are, the more force is being added. Physics To Go 11/14/10 ﻿1) The force from the shot put is equal to the force of the person's hand, but the force is in the opposite direction. 2) Because of the normal force exerted on the chair from the ground. Because the objects aren't moving, there is no acceleration which means that the force applied for all of them will be equal. There is deflection on the floor because of the chair, and there is deflection on the chair because of the mass of the person. 3) It works because it is measuring your weight with the force of gravity on you. 4) The force of the ball on the bat, and the bat on the ball is equal, but in opposite directions. The bats force is towards the ball and the ball is towards the bat. The bat probably sometimes breaks because of too much acceleration from the ball. 5) If a big linebacker tackles a small running back, the linebacker will have more force and will probably knock the running back over. This is because of his larger mass. 6) When a hockey player hits the wall, he has normal force and weight from gravity. The normal force is both from the ground and towards the wall. The weight from gravity's arrow is pointing downward. 7) Because the higher the acceleration of the ball, the bigger force it has. The bigger the force, and the faster that the ball is landing, makes it harder to catch. The ball will hit the person's hand a lot harder, and the glove protects that. 8a) The quarterback throws the ball. He catches it and runs down the field with the ball. A larger sized and bigger massed person tackles the player. The two players exert equal force on the other and they both go backwards. Their forces were opposite but equal. b) Deflection on the ground can produce a normal force. When a person is running, each step they take, they are deflecting the ground. The ground is being pushed back, and therefore, pushing them forward. What Do You Think Now? 12/15/10 ﻿You have to bend your legs when you're jumping. This helps you jump higher. As you jump, you are applying force to the ground, and the ground will apply a force as well. You will push up with a normal force. It'll apply the same force but opposite directions in the same force as before.

Section 7
What Do you Think? 12/15/10 Some sports require special shoes because of the way that you have to run, walk, jump, etc. Every sport is different, so you have to do different things for different sports, which means we need different shoes.

Physics Talk Summary 12/15/10 In Newtons second law he says that an object can move at a constant velocity if there is a net force of zero. Friction is a force that keeps things moving without any acceleration. It resists relative motion between and object and a surface, and has to do with something being pulled on a surface. The forces are in opposite directions, making the net force zero. An object being pulled won't travel in a vertical direction, so the vertical force must add up to zero. The upward force (normal force) must be equal to gravity as well. Normal force is perpendicular to the surface or the object's weight. The coefficient of sliding friction is represented by µ. It is the ratio of friction to the normal or perpendicular force. The force of friction is equal and opposite in direction to the force needed to pull an object. Sliding friction has no units because it is a force divided by a force so the units cancel out, it is expressed in decimal form, it changes when the surfaces change, and the perpendicular force is equal to weight, so if the surface isn't flat it will change.

Checking Up Questions 12/15/10 1) You can say that the force pulling the shoe is equal to the friction on the shoe at constant speed because of Newtons second law. It supports this theory that forces must be equal but opposite in direction. The net force must be zero for something to move in at a constant velocity. 2) The coefficient of friction has no units because a force is being divided by a force, so they cancel each other out. 3) The coefficient of friction is determined by the ratio of the friction to the normal force.

Physics To Go 12/19/10 1) When it rains and you're playing soccer the grass gets wet and slippery and there is less friction. The ball rolls a lot more and the players tend to slide. The players where cleats though which grip the ground a little better so when it does get slippery, they tend not to fall. 2) When a person is running, they don't want to have friction because they want to be able to run as fast as possible. Track runners wear lighter shoes so that there isn't as much friction between them and the track. 3) No, you would need to test the friction caused by this surface because each surface is different. 4) I think they do have shoes for each surface, clay, grass, and hard, because the different surfaces cause different amounts of friction. There sneaker should be the one that causes the right amount of friction for them. 5) µ= F/N .03= F/ 600 = 18 N 7) Air resistance and water resistance remain constant if you are running at a constant velocity. This is because when I am playing a sport I am able to keep a constant and quick speed. It doesn't get harder to run because there is the same air resistance acting on me as I run. 8) The stronger legs you have, the faster you are able to accelerate, but shoes with maximum friction still wont allow you to run as quick as you can even with really strong legs. To reduce friction and accelerate quickly, you can buy shoes with different bottoms in order to help you run quicker. The smoother the bottoms are and the lighter the shoes, the faster you can accelerate. 10) Friction is important in running because without friction, runners would usually fall. There wouldn't be anything holding them up and they would be sliding around the track. Cleats are good for friction because they allow the player to dig into the ground and allow them keep their balance better. 11) The runner is about to start racing around the track against his opponent. This should be an easy race for him because he just got brand new shoes that are lighter providing him with good friction but not enough to slow him down. His opponent is wearing heavier basketball sneakers which is slowing him down while he is running. There is a lot more friction and he won't be able to accelerate as fast.









Questions: 1) It means the friction nad weight of the block and mass. 2) It is around the same as everyones in the classroom. They should be able the same since it is in the same surface and it is about the same size wooden block. 3) My times mostly agree, but they were a little off. My percentages weren't high, but they weren't very low. 4) They do apply in the real world because if you play a sport it is important to know what kind of shoe to buy that is best for the friction and won't make you slip. 5) Slow reaction time, weren't that precise, random error.

What Do You Think Now? 12/22/10 Some sports require special shoes because the shoe will affect how much friction is added. A shoe with a smooth bottom won't have a lot of friction, so you use those kinds of shoes on a surface with a lot of friction. The heavier the shoes you wear the more that they will not slip. The coefficient of friction shows how much friction is present when the normal force and friction are applied.

What Do You Think?
1/3/10 If they ﻿are going 6 with 5.5 then they will not be able to go 12 with 11 because they might not be accelerating enough to go over the wall. Speed, as well as what angle you put the vaulter in the ground, is one of the most important things to factor in when you're trying to figure out how high to go.

Physics Talk Summary 1/3/10 The speed and position of an object changes when a force is applied. When the speed and position is changed, the object is able to go back to its original speed and position,which is the concept of energy. There are two types, kinetic energy, which deals with motion, and gravitational potential energy deals with the position of the object and its vertical launch. The energy changes when a force acts on an object. The sum of the kinetic energy and potential energy, is the total energy stays the same. This is why objects are able to go back to their original position and speed. It can be transferred from one form to the other but the total energy stays constant. When a force is applied to an object, with the same or opposite direction for a distance, it is called work. Work is the force multiplied by the distance. When work is done the energy of the object changes. Energy that form a spring because of compression or stretch is elastic potential energy.
 * ==== Type of Energy ==== || ==== Description ==== || ==== Equation ==== ||
 * ==== Kinetic Energy ==== || ==== Energy possessed by an object when it is moving ==== || ==== KE=1/2mv^2 ==== ||
 * ==== Gravitational Energy ==== || ==== Energy possessed by an object when it is above the lowest point. ==== || ==== GPE= mgh ==== ||
 * ==== Elastic Potential Energy ==== || ==== Energy possessed by a spring when stretched or compressed. ==== || ==== EPE= 1/2kx^2 ====

x= distance stretched or compressed.
||
 * ==== Work ==== || ==== Caused by a force acting over some distance parallel to the direction of motion. Not really "energy", but creates energy ==== || ==== W=F(d) ==== ||

Checking Up Questions 1/3/10

1) A force needs to act on an object for energy to change.  2) A penny launched gets its energy from the ruler it was launched from, the ruler has elastic potential energy.  3) The vaulter needs to get a running start first which gives him kinetic energy which he needs to get high, and catapult. He also needs elastic potential energy from the pole which bends as he is flying. Then he needs potential energy as the pole straightens, and lastly as his height changes, he needs gravitational potential energy to launch him vertically.  4) Units:  kinetic:  potential:

Physics To Go 1/4/10 1) When the person is holding the shot, there is gravitational potential energy because it is above the ground. Once it is released, there is kinetic energy as it is increasing speed. When the shot put reaches its highest point, there is gravitational potential energy again because it's velocity is zero, and it is above the ground. There is kinetic as it is falling again and as it hits the ground there is work done by the ground to stop it. 2) When a golf ball is hit into the air there is kinetic energy. When it reaches it's highest point, there is gravitational potential energy because it isn't moving and about the ground. As it falls back down to the ground there is kinetic energy again, and when it hits the ground there is work. 3) KE=GPE- 1/2mv^2=mgh-1/2(12)^2=(9.8)h-72=9.8 h-h= 7.35 meters 4.) The length of the pole doesn't determine the height that a person can jump to because the pole doesn't have anything to do with the energy needed to left the person because it mostly deals with the velocity of the persons running that is in the beginning. 5.) The poles temperature rises while it flexes because the vaulter is using his kinetic energy while running until he sticks the pole into the ground. At this time the energy is being transferred due to the conservation of energy, and this energy makes the poles temperature rise. 6.) KE=GPE- 1/2 mv^2= mgh-1/2v^2= (9.8) (4.55)-v= 9.44 m/s 7.) Emmas: 1/2 mv^2= mgh- 1/2 v^2= (9.8) (4.55)-v=9.44 m/s Sergei's: KE=GPE  1/2v^2=gh- 1/2 v^2= (9.8)(6.14)-v=10.97 m/s Sergei's speed was 1.53 m/s faster than Emma's which made him go higher up.  8a.) GPE (mgh)= W = KE= 1960 J  KE= 1/2 mv^2 1960= 1/2 (2)v^2 v=44.27 m/s 8b.) You can calculate this without the mass because the masses in Kinetic energy and Gravitational potential energy cancel out because they're equal. 9a.) W= EPE- F(0.3)= 1/2 kx^2-W= 1/2(1500)(.25)^2-W= 46.875 J 9b.) EPE= KE  1/2 kx^2 =1/2 mv^2- 1/2 (1500) (.25)^2= 1/2 (.1)v^2-30.6 J 10a.) EPE=W- 1/2 kx^2 =FD 1/2 (315) (.3)^2 = W- W=14.2 J 10b.) W=FD 14.2=F(.3)- 47.3 J 11.)GPE=EPE mgh=1/2 kx^2- (.04)(9.8)(1)= 1/2 (18) (x)^2 x=.21 J 12a.)  12b.) 12c.) 12d.) 13.) EPE -->KE -->GPE -->KE 14.) KE=W =GPE 15.) THe pitcher throws the ball towards the player, the ball has kinetic energy. The ball has kinetic energy when it is hit in the air. Once it reaches its highest point, the ball has gravitational potential energy with a velocity of zero. As it falls back down to the earth there is kinetic energy and after hitting the ground, the ground does work. 16.) The soccer ball rolls towards the player it has kinetic energy as it is moving towards him. The player runs in the direction of the ball and uses energy in order to do work. The ball now has gravitational potential energy as it is rising up after being kicked. Then the balls hits the ground in the goal.

Investigate 1/3/11 ﻿Prelab: a) You place the ruler on the table, the half of the ruler that is holding the penny over the table, and then you push that part of the ruler down and you let go and it flies up.  b) It was flat down on the table, half of it on the table and the other half hanging off the table and we did not bend it too much so it did not hit the ceiling. It depends on the force you use and the elasticity of the material, the length of the ruler, the placement of the penny, and the mass of the object. 1) LENGTH OF THE RULER:
 * Centimeter observations off the table. || How far penny is projected in the air. || Observations. ||
 * .5 cm || 46 cm || After two trials the penny reached between 40 and 50 cm. ||
 * 1.0 cm || 73 cm || After two trials the penny reached between 70 and 75 cm. ||
 * 1.5 cm || 126 cm || After two trials the penny reached between 120 and 130 cm. ||
 * 2.0 cm || 184 cm || After two trials the penny reached between 180 and 189 cm. ||

What Do You Think Now? 1/5/11 Champion pole vaulters can't vault over a 12.0-m high bar with a pole 11 m long because it isn't the height that depends how far you go, it is the speed. Kinetic Energy must be equal to Potential energy because it decides how high you can go. The law of conservation of energy states that energy can't be created or destroyed, it's equal.

Section 9
What Do You Think? 1/6/11 ﻿I don't think that hang time affects the pull of gravity for some athletes, because no matter how long you're in the air for you have to come down eventually, which is the pull of gravity. I don't think world-class skaters defy gravity because they still come down no matter how long they were in the air for they can't stay up there forever.

Investigate 2) The skater was in the air for 20 frames. 3) 1/30 second (20 frames) = 2/3 second 4) During the middle frames the skater seemed to hang in the air. During frames 5-8 the skater seemed to hang in the air defying gravity. 5a) The player was in the air for 31 frames b) 31(1/30) = 31/30 seconds c) The basketball player was in the air for a longer time than usual but he was still not defying gravity.

1) First you bend your knees. Work is involved because you are causing work on the floor. Then you're in the air for some amount of time, and you go up a certain height off the floor. As you are going up you are using kinetic energy. When you reach the highest point, there is gravitational potential energy. 2a) The more force that you use, the higher up you will go. b) We will record the height that you are in the air and we will need to know our mass in newtons. c) We will use a meter stick to measure out height d) Our data will be in a chart made in data studios. This graph will compare the force in our jump from pushing off the ground to the time that we are in the air. 4) My force calculated: W= GPE FD=mgh f(.18)= (120)(9.8)(.35) F= 2286.27 My force on scale: 983.53 5) My calculations were far off from the calculations on the square.

% error= 1 calc-exp/ calc (100) % error= 2286.27-1352.56/2286.27 (100) % error= 40.84

Physics Talk Summary 1/6/11 Peak position is where there is gravitational potential energy. When you are about to jump and your knees are bent you have elastic potential energy. Although there is no spring, the chemicals in your muscles provide the potential energy. This energy changes to kinetic energy when you are jumping. A person who can jump higher has more gravitational potential energy and a higher peak point. A table can be used to show the amounts of each type of energy. It would show the position and then each type of energy and how many joules you are using for each. The total energy must be conserved. If you are jumping on a trampoline instead of a hard floor, your kinetic energy coming down would change to elastic potential energy because of the springs when you are coming back up. A specific object can lose or gain energy but the whole system must keep equal energy.

Checking Up Questions 1/6/11 ﻿1) It comes from elastic potential energy when you are bending your knees. The energy comes from chemicals in your muscles. 2) In the launch position and at the peak of your jump, the person will have gravitational potential energy. As they are jumping up though there will be kinetic energy, then it turns into gravitational potential energy. 3) Nuclear energy, sound energy, and light energy are all different types. They are energies due to heat.

Physics To Go 1/7/10 1) W= GPE FD= mgh W=50 (9.8)(1) W= 490 J 2) W + GPE ---> Kinetic energy --> Work 3) In order to test this we would watch the video like we did in class in slow motion scene by scene. We would check to see if the player moves in a parabola like form which means that he is not hanging in the air. 4) Although it may seem like the laws of gravity can be defied when doing sports like ice skating, it is not true. The person might have evidence that seems to be true but it is not. The arguing person could explain that it looks like they are defying gravity because of how small their displacement is. 5) A person can increase their vertical jump by bending their knees farther down which increases their elastic potential energy and by decreasing your mass. 6a)W=FD W=1(1)= 1 J b.) W=FD W= 1(10)= 10 J c) W= 10 (1) W= 10 J d) W= FD W= .10(100) W= 10 J e) W=FD W= 100(.10) W= 10 J 7a) GPE= 1 J b) GPE= 10 J c) GPE= 10 J d) GPE= 10 J e) GPE= 10 J 8a) KE= 1 J b) KE= 10 J c)KE= 10 J d) KE= 10 J e)KE= 10 J 9)W= FD W= (50)(43) W= 2150 J 10.) KE= 1/2mv^2 KE= 1/2 62(8.2)^2 KE= 2084.4 J 11a.) a= f/m a= 30/5 a= 6 m/s^2 11b.) W=Fd W=30 (18.75) W= 562.5 J 12a.)W= FD 40,000=3200 N (d) D= 12.5 meters 12b.) a=f/m a= 3200/1200 a= 2.7 m/s^2 13.) KE--> W KE= W 1/2 mv^2= FD 1/2 (.150) (40)^2= W 120 J= W 14.) W= KE FD= 1/2 mv^2 417d= 1/2 (64) (15)^2 417d=7200 d=17.27 meters 15.)
 * || KE || GPE || EPE || Sum ||
 * Running || 100 J || 0 || 0 || 100 J ||
 * Full Bend of pole || 10 J || 0 || 90 || 100J ||
 * Peak Height || 0 || 100 J || 0 || 100 J ||
 * Landing || 40 J || 60 J || 0 || 100J ||
 * Cushion Collapse || 0 || 0 || 0 || 0 ||

16.) 17.)
 * || KE || GPE || EPE || Sum ||
 * Peak Height || 0 || 1000 J || 0 || 1,000 J ||
 * Landing || 100 J || 400 J || 500 J || 1,000 J ||
 * Lowest height || 0 || 0 || 1,000 J || 1,000 J ||
 * || KE || GPE || EPE || Sum ||
 * Top of Mountain || 0 || 1,000 || 0 || 1,000 ||
 * Middle of Mountain || 500 J || 500 J || 0 || 1,000 J ||
 * Bottom of Mountain || 1,000 J || 0 || 0 || 1,000 J ||

18.) The basketball player is about to take a shot. He dribbles down the court at full speed. He has kinetic energy. He then jumps up in the air in a parabola like form. He is able to jump really high and far because of the amount of kinetic energy he had. At the highest point, he has gravitational potential energy. He then shoots the ball and falls back down to the ground with kinetic energy.

Physics Plus

1a) GPE= GPE +KE mgh= 1/2 mv^2 +mgh  9.8(50)=1/2 v^2 +(9.8)(30)  490=1/2V^2+294  v= 19.8 m/s  b) The mass cancels out because it is independent so you do not need it. 2)GPE+EPE=KE mgh +1/2kx^2= 1/2mv^2  .3(9.8) (2) +1/2 (60)(.4)^2= 1/2 (.3)v^2  10.68=.15v^2  v=8.4 m/s  3) GPE+W=GPE+KE+W mgh+FD=mgh+FD+ 1/2mv^2 200(9.8)(25) +200,000=1/2(200)(9.8)h+50,000 249000=210000+1960h h=19.9 meters

What Do You Think Now? 1/11/11 It is impossible to defy gravity. If you watch them in slow motion or in different frames you would see the player moving up and then down very slightly each time. Figure skaters have enough kinetic energy to stay in the air longer. They use the conservation of energy because they know that the more kinetic energy they have, the longer they will be able to stay in the air because this energy is converted into gravitational potential energy.