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= = = = toc =**Chapter 2: Section 1**=

http://news.sciencemag.org/sciencenow/2010/09/impossible-soccer-goal-explained.html The player was able to kick the ball that it went 35 feet and went to the left of the goalie. He originally kicked it to the right but in mid-air the ball dropped and went to the left. This happened because the weight of the ball. If it was a smaller ball it wouldn't have been able to drop as easily as the bigger ball did.
 * 11/8/10 - Sports Article**

There is a soccer game going on in the picture. Its showing the motion that it takes for a player to run up and kick the ball (The force that it takes to get the ball to pass over the net). It also shows the path of the ball as it goes over the goal net. It also shows a boy kicking the ball up in the air and reaching the ground with a very steep curve. There is a mouse and bug that is trying to push the ball but they're too small to move the ball. The bug cannot move the ball and the mouse can only push the ball. The ball weighs more than the mouse and bug and they don't have enough force to get it to move. The more power you give into moving it, the further it will go.
 * What do you see?**

The ice skater needs to give enough force (pushing their legs off the ice) to get them to move so far across the ice and to continue moving at a high speed. Because ice is slippery, the skater can move with ease and slide with the force from their legs. There is also no force acting against them. The soccer ball continues to roll across the field after it has been kicked because of the force behind it. It will stop when the force that was originally given does not have the force it had.
 * What do you think?**

1. Set up the simulation and run the first trial. 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. //**5.01 m**//  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. //**5.01 m**// 2. 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. a) Predict where the skater will reach his highest position if he begins at the same place as before. //**5.4 m**// b) Explain why you think so. //**I think he's going to go a little further than his initial height because he has more speed building up.**// 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 .39 m off. I thought that the skater would go further but he ended up at the same height that he started at. My guess was very close.**// 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 skater ended up exactly where he started. He started at 5.01 m and ended at 5.01 m.**// 4. Repeat Steps 2 and 3, creating an even less steep slope. a) First record your prediction. //**I think the skater will go further because the slope is longer and straighter.**// b) Compare your prediction with the outcome. //**The skater stopped at the same height that he started at. (5.01 m)**// 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 the other half of the track is in a straight- horizontal line.**// b) How far do you think the skater would roll? //**I think the skater will roll until he falls off.**//  c) What would keep the skater rolling on a horizontal track? //**The force from the skater's original height.**// d) Try this on the simulation. What happens? //**The skater rolls until he falls off the track and then continues to roll.**// 6. Conclusion Questions: a) What happens to the length of the opposite track the skater rides as the slope decreases? //**The length of the opposite track gets longer.**// b) What happens to the final vertical position on the opposite track the skater rides as the slope decreases? **//If its horizontal, there is no height for it. If there is still a slope then it will end at the same as the initial height.//**  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 initial height is the same as the height on the opposite side of the track.**// d) If the opposite track was infinitely long, and frictionless, when would the skater stop? //**The skater will stop once the momentum from the force going down the ramp runs out.**//
 * Investigate**

//Galileo's Law of Inertia// //Newton's First Law of Motion// //Running Starts// //Frames of Reference//
 * Physics Talk - Summary**
 * Objects will continue to move as they already are.
 * Inertia is the natural tendency of an object to remain at rest unless a force acts on itor to remain moving with constant speed in a straight line.
 * Inertia: Property of matter that resists changes in motion (acceleration).
 * Measured --> Mass
 * Units = kg
 * Velocity: Change in direction or speed; Acceleration: How fast your velocity is changing (velocity changes quickly: fast acceleration, velocity changes slowly: slow acceleration)
 * After Galileo, people thought about how moving objects might continue to move forever unless a //force,// a push or pull, stopped them.
 * He realized that objects do not stop "on their own" but stop because there is a frictional force working that you cannot see and that is the force that stops the object
 * 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.
 * Mass is a measure of its inertia, or tendency to resist a change in motion. Given different masses moving at the same speed, the one with the greatest mass has the greatest inertia.
 * 1 kg = 1000 g
 * In sports, where the object is to maximize the speed of an object or the distance traveled in air, the prior motion of a running start is very important.
 * Increase distance and/or speed to give advantage
 * In javelin: The hand has a forward speed relative to the elbow, the elbow has a forward speed relative to the shoulder, and the shoulder has a forward speed relative to the ground because the body is rotating and the body is also running forward.
 * The //speed// of the javelin is the sum of each of the speed ^^. If the thrower is not running forward very fast, then the running speed does not add very much to the javelin's speed relative to the ground.
 * v(javelin) = v(hand) + v(elbow) + v(shoulder) + v(body)
 * Velocity is speed in a given direction.
 * Acceleration occurs during starting, stopping, and changing direction.
 * If you can run at 5 m/s, then the ball will get the addiction speed of 5 m/s when you throw it. The ball's speed is the sum of your speed before releasing the ball.
 * Toy cannon on a skateboard: The toy cannon shoots a small ball forward at 7 m/s. The skateboard is moving at a constant speed of 3 m/s. The ball's speed is now 10 m/s. (7 m/s + 3 m/s = 10 m/s)
 * Frame of reference is a vantage point with respect to which position and motion may be described.
 * If you run down a plane moving at 400 mph and you're running at 5 mph then from the ground you'd look as if you were moving at 405 mph. If you turned around and ran the other way then you'd look like you were running 395 mph from the ground.
 * "Relative to another object" adding or subtracting velocities

1. Inertia is the property 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 is when there is an 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 in a straight-line path. 3. Friction or an unbalanced force needs to act on an object to stop it from moving at constant speed. 4. Friction. 5. If there is a 1 kg cart moving at 3 m/s or a 6 kg cart moving at 4 m/s then the 4 kg cart will have a greater inertia. The greater mass. 6. Its going to be different if the person is standing inside or outside of the train.
 * Checking Up**

1. a) The ball will roll forever. b) An object in motion, stays in motion until an unbalanced force acts on it; you couldn't tell exactly when it would stop unless there was something that acted on it to stop it from moving any further. 2. It would reach 20 cm on the opposite side of the ramp and then roll back down. 3. No I don't think this is possible because if an object was able to stay at a constant speed forever then there would be things hitting into each other everywhere. There would be no force in the world acting against the object. There will also never be a frictionless situation. 4. When the stick hits the puck the force behind the puck is so strong that the puck will keep going until it hits something. When it hit something, the puck would bounce back because the force from the stick was so strong. 10. a) Soccer: When a player kicks a ball (at a running start) the ball continues to roll until another player kicks or stops it. (motion that stays in motion); hockey: A hockey puck is hit with a hockey stick and continues to move until another hockey stick stops the puck from moving further; chess: the pieces do not move unless a person moves a piece. There also isn't much friction no ice. b) In sports news, Jerry kicked the ball and it didn't stop! It didn't stop until Harry kicked it back towards Jerry. It was crazy. The momentum the ball had and the power it took to stop and start the motion of the ball! CRAZY! Hockey, same sorta deal. George was able to hit the puck so hard that it did not stop until it slammed against the wall of the ice rink. It bounced back and George was able to grab control of the puck again. I don't think I saw that puck stop once!!!! In other news, chess pieces stayed at rest. It was crazy. No motion, just rest
 * Physics-To-Go**

-A figure skater keeps moving across the ice at high speeds for long times with barely any effort because there is not a lot of friction on ice. They can glide across without anything really stopping them. -A soccer ball continues to roll across the field after it has been kicked because the force from the person who kicked it. It stops when a force acts on it. -Their horizontal speeds are determined by the force that was originally put on them. The push from the legs for the ice skater and the running person who kicked the ball. They keep moving without someone doing something to them because of their starting force.
 * What do you think now?**

1. http://scienceblogs.com/builtonfacts/2010/02/the_physics_of_curling.php By sweeping the ice, more friction is removed making the puck go further. It starts off with a push and continues to move because of the frictionless surface underneath it.
 * Inquiring Further**

=Chapter 2: Section 2=

I see a boy walking slowly and a dog walking slowly not really thinking about much. There is also a snail that is moving faster than both of them. His foot prints show small strides which shows how slow he is walking. In the second picture the boy sees his "love" and runs with flowers in his hand. The force and reason of his running was seeing someone he liked. The dog also is running and the boy seems to be catching up to him. There is no snail in the picture either. His strides are also longer which makes him move faster.
 * What do you see?**

The 100 mi/h and 45 m/s shows how fast the ball in moving compared to the ground. The momentum and force from the player winding up and throwing the ball is how fast the ball is going to go.
 * What do you think?**

//Measuring Motion// //Calculating Speed// Calculating Acceleration: When an object changes its speed //Acceleration +v -v//
 * Physics Talk - Summary**
 * Speed and acceleration can bee seen through the ticker timer.
 * Constant speed: Distance between ticks were equal
 * Slow, constant speed: Distance between ticks were shorter than when you travelled faster
 * Fast, constant speed: Covering more distant than travelled slow
 * When accelerating: distance between the dots on the tape were not equal
 * When gradually accelerating: distance between dots gradually got longer
 * When gradually decreasing speed: distance between dots gradually got shorter
 * Average speed: distance traveled divided by the time taken to travel that distance. How fast position changes
 * Large distances or times over which there there may be variations.
 * Average Speed = distance traveled / time elapsed
 * Instantaneous speed: Speed at that moment
 * Acceleration = change in speed / time interval
 * Positive accel. +a incr. v dec. v
 * Negative accel. -a decr. v incr. v

1. a) Constant speed: evenly spaced b) Positive Acceleration: Distance between the dots got longer c) Negative Acceleration: Distance between dots got shorter 2. Vav = d/t Vav = 400 / 50 Vav = 8 m/s is the runner's average speed 3. Instantaneous speed is the speed travelled in a certain moment. Average speed is the distance traveled divided by the time taken to travel that distance. 4. A = (Delta) speed / Time interval A = 100 / 10 A = 10 m/s is the vehicle's average acceleration
 * Checking Up**

km/h x 1000mm/1km x 1h/3600 s 1. Average speed is not exact. It can vary from a lot faster to a lot slower. Instantaneous speed is the speed at a moment. 2. a) Vav = d/ t Vav = 1 / 15 m/s or 66 m/s b) Vav = d / t Vav = 84 / 6 Vav = 14 m/s c) Vav = d / t Vav = 9.6 / 2 Vav = 4.8 km/h d) Vav = d / t Vav = 400 / 4.5 Vav = 89 km/h 3. a) negative acceleration b) positive acceleration c) no acceleration (zero) d) negative e) no acceleration (zero) 4. a) a & d b) b c) a d) c e) a: positive b: zero c: (+) then (-) d: positive 6. a) 45 km/h x 1000 m / 1 km x 1 h / 3600 s = 12.5 m/s a = (delta) v / (delta) t a = 0 - 45 km/h / 9 s a = -1.4 m/s^2 b) negative value 7. a) Constant b) positive c) slow constant --> increasing -->faster constant --> deer --> slow const. d) deer --> constant --> increasing 8. Vav = d / t Vav = 100 mi / 2 h Vav = 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. Accelerating and then constant 11.a = (delta) v / (delta) t 4 m/s = (delta) v / 5 m/s 4 m/s every second 20 m/s 14. a) runner b) car racing c) walking a dog d) running a race e) gymnast on a trampoline (Stopping when hitting a trampoline)
 * Physics To Go**


 * Physics Plus**

100 mi/h means that for every hour you're traveling 100 miles. If you travel for 4 hours, you are traveling 400 miles. No one ever goes that speed because of how fast it is. 45 m/s means you're traveling 45 meters in a second. If you travel 2 seconds, you'd be traveling 90 meters.
 * What do you think now?**

=Chapter 2 : Section 3=

There is a girl pushing a ball while walking, then she starts to jog while continuing pushing the ball, then she runs and is pushing the ball. Her hat falls off and she seems to be sweating. There is a dog driving in a car and seems to be going fast while the girl is running.
 * What do you see?**

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.
 * What do you think?**


 * Physics Talk**
 * An equation for Newton's First Law of Motion
 * Acceleration = force / mass
 * A = F / m
 * F = m x a
 * a = F / m
 * m = F / a
 * 1 N = 1kg x m/s^2
 * Acceleration due to gravity: 9.8 m/s^2 ON EARTH
 * Force of a ruler, a spring, a rubber band, a magnet, a hand and a bat hitting a ball.
 * Newton's second law: acceleration is caused by unbalanced forces
 * If you push a small cart with the largest force you can, the cart will move a very far distance. If you push a car with that same force, acceleration will be much smaller.
 * Calculating Newton's Second Law of Motion
 * F = mt x a

1) Newton's second law of motion is acceleration equal to force divided by mass. 2) If the mass is greater, the force will be less. If the mass is less than the force will be great and the object will move fairly far.
 * Checking Up**
 * 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 due to the lower gravity. **

1) 350 N 80 kg 10 m/s^2 80 kg -15 m/s^2 -3000 N 3) a = F / m a = 42 N / .30 kg a = 140 m/s2 4) F = m x a F = .040 kg (20.0 m/s2) F = .8 N 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, stopping it is going to be very difficult 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. 6) .98 N about .98 newtons for 5 bucks! the .98 newton burger 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) 50 N + 40 N = 90 N 11) 200 N X 4 = 800 N 12) a = f / m 125 = .700 kg x a 179 m/s^2 13) 130 N 67 degrees NE 14) 6403 N 39 degrees 15) F = m x a F = (12.8 kg) (9.8 m/s^2) F = 125.44 N 16) a) 50 N 53 degrees b) 8.9 m/s^2 17) a) 36 N 34 degrees b) .36 m/s^2 c) If both net forces were pushing to the left then it would be 50 N. It would move at .5 m/s^2 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 acceleration will be very large. Putting in the same about of force on a larger object, the acceleration will be a lot slower. In our case, with tennis. the force put on the ball can't be too strong or the ball will go out of bounds. The ball is about 5.6 kg and if the net force is around 100 N, then the acceleration of the ball will be 17.8 m/s^2.
 * Physics To Go**


 * Physics Plus**

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 very great. 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.
 * What do you think now?**

=**Chapter 2, Section 4**=

A girl is throwing apples and the boy is timing the distance that the apples go. The apples are let go at the same point but one is thrown and the other is dropped. The green apples are moving at constant motion but the red apples are moving sparatically.
 * What do you see?**

The mass of the object determines how far the object will go. If it is a larger object it will not travel as far before it hits the ground. If it is a lighter object it will move farther. If the force is greater than the object will go further depending on its mass. If little force is given, it will not go as far.
 * What do you think?**

//Projectiles and Trajectories//
 * Physics Talk**
 * Projectile: The only force is weight. Launched through the air. Ignore air resistance.
 * ay = -9.8 m/s^2 (downward)
 * ax = 0
 * If ^^ aren't true, it is NOT a projectile
 * Trajectory: Path of a projectile (parabolic shape vv)
 * 10 m/s each second until 0 then negative 10 meters per second each second
 * Ground to ground: symmetrical around the highest point (y-max, Vy=0) x and y information are independent from each other
 * Horizontal launch
 * Free-fall
 * The only force is weight but it is one dimensional motion (only vertical)
 * Vertical positions of a free-fall and projectile are the same


 * Vertical components of velocity decreases on the way up.
 * Vertical components of velocity increase on the way down.
 * Horizontal components of velocity do not change.
 * Trajectory is path, resultants all strung together.

1. They will reach the ground at the same time. (no air resistance) 2. No, the object speeds up. 3. When its upward its at 0 and going down it is decreasing to a negative acceleration.
 * Checking Up**

1&2) 0 - - - 1 - - - 2 - - -
 * Physics To Go**

3 - - -

4 - - -

5 - - -

4) I surveyed 5 people. 4 of the 5 thought that the bullet that is dropped will reach the ground first. Only 1 thought that the horizontally shot bullet would reach the ground first. Neither said that they would hit the ground at the same time. I think that people have a hard time believing this because if you shoot a bullet it tends to go pretty far rather than just dropping a bullet. 6) The horizontal motion does not affect the motion of 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.

1 & 2) 2. a) They hit the ground at the exact same time. If there is no air resistance, the same amount of gravity is being used on them so they will hit the ground at the same time. 3. a) No the faster speed does not depend on if they hit the ground at the same time or not. They hit the ground at the exact same time. b) Yes, it lands a lot further.4. a) The height does not affect wether the coins hit the floor at the same time. The horizontal coins do not travel as far at lower heights. 5. a) The ball will move with the person as they throw it up in the air while moving. 6. a) Decreases on the way up, the horizontal components do not change, and the components of velocity increase on the way down. b) The speed affects the range because if you speed up than the ball will land behind the chair. If you go too slow or stop then the ball will land ahead of the chair. 7, 8, & discussion questions)
 * Investigate**


 * Physics To Go**


 * What do you think now?**
 * The initial velocity, height, and angle at which an object is launched determine how far it will travel before landing. **

=**Chapter 2,** **Section 5**=

I see a ball being kicked vertically then coming down and hitting another person on the head with the ball. The ball bounces off of the other person's head into the goal. The greater the initial velocity of the ball, the greater its range will be. If several objects are launched from different angles with the same initial velocity, and the theta is between 0 and 540 degrees, the range will increase as the the angle increases. If the same is true but the theta is between 45 and 90 degrees, the range will decrease as the angle increases, down to 0 degrees. 45 degrees is the maximum range.
 * What do you think?**

-Constant speed in a straight line, corresponding to the amount of launch speed and its direction -Downward acceleration at 9.8 m/s^2 -In real world: Air resistance makes balls in sports more complex so they don't follow a perfect parabola.
 * Physics Talk**
 * - Projectiles have two motions that act at the same time yet don't effect each other. **
 * - Mathematical Model: table of times, speeds, and distances during falling **
 * - Physical Model: evenly spaced strings of calculated lengths **

1) Constant speed in a straight line and downward acceleration at 9.8 m/s^2. 2) The model must be realistic. **Air resistance.** 3) The height increases as the range decreases. **The downward gravity of it will increase.**
 * Checking Up**


 * Physics Plus**

1. At 45 degrees it produces the greatest angle 2. a) Greater than 45 degrees (more time) b) Less than 45 degrees (less time) 3. a) 30 degrees = 60 degrees **90- 30 = 60 degrees** b) 15 degrees = 75 degrees **90- 15= 75 degrees** 4. This occurs because x is greater than y, the angle always has to be less than 45 degrees. Also because it is jumping, rather than running. 5. He is very good at running horizontally ( x-component) which related to the the long jump because you run into it and are traveling forward not upwards. 6. a) The acceleration direction of the ball isn't up or down, it is both of the directions working against each other at acceleration of zero. b) The velocity is zero. 7. b) c) 8. 45 degrees creates the longest range 9. The angle closest to 90 degrees makes the greatest projectile height 10. a) east b) c)
 * Physics To Go**
 * vix > v iy the angle has to be less than 45 degrees**
 * Fast x-velocity, fast y-velocity. Large maximum height**
 * a= -9.8m/s^2 down**
 * || x || y ||
 * vi || 5cos0=5 || 5sin0=0 ||
 * a || 0 || 9.8 ||
 * d || 15 m ||  ||
 * t || 3 || 3 ||
 * vf || 5 ||  ||
 * 64m from the cliff**

At an 80 degree angle it will go less of a distance that a 10 degree angle. At 45 degrees it will go farther than 70 degrees. If there is a larger launch speed than the object will go farther. The acceleration on the way up increases by the same time intervals until it reaches 0, then it negates and goes down with the same time intervals between as it was going up.
 * What do you think now?**

=Chapter 2, Section 6= There is a boy pushing himself back from a wall. He looks like he's struggling but once he pushes back he is relieved. The force coming from the wall causes the dog to even get winded. Also the girl in the window seems to be affected by the push. The wall moved because the push was so hard.
 * What do you see?**

Push off the ground. Squat and push the force to the bottom of your body. Straighten your knees while pushing off the ground. Be sure to bring both of your feet off of the ground. The force that you push on the ground pushes back on you causing you to go up.\\ Checking Up
 * What do you think?**

1. Newton's third law of motion states that if one object acts on another, the same amount of force is transfered between the two objects. 2. Since earth pulls down a certain mass with the force of gravity, gravity is also acting upon the earth, pushing objects that are pushing up, down. 3. A free body diagram illustrates the different forces acting upon an object
 * Check**

__Newton's 3rd Law__: For every action, there is an equal but opposite reaction. 1. Newton's third law of motion states for every applied force, there is an equal and opposite force. Also, forces always come in pairs. 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
 * Physics Talk**
 * All forces come in pairs
 * Each acts on a different system
 * They must be __equal__ in size but point in opposite directions
 * Collision > forces must be equal
 * Ball on bat is equal to bat on ball
 * Checking Up**

1. Yes, due to Newton's third law 2. The chairs are not intelligent, but the gravity of the earth pushes the same force that is being exerted on the chair. If materials cannot handle a force then the material breaks. 7. Padding reduces the force. It acts like a cradle when you pull back your arm so the force doesn't hurt as much.
 * Physics To Go **

The force from the ground will push back on you when you push down on the ground. Apply a great amount of force to the ground and it will exert the same amount of force on you. You will go higher with the more pressure you push down.
 * What do you think now?**

=Chapter 2, Section 7=

The shoe that the girl is pulling on the ice moves very easily but the shoe on the sand is harder to pull and it seems close to impossible for her to move it.
 * What do you see?**

You need certain shoes for different sports so that they work with the surface you are performing on top of. In basketball, you can't use golf shoes because it will destroy the floor. While playing baseball you need spikes at the bottom of your shoes so there is enough friction so you don't fall on the dirt or the grass.
 * What do you think?**

 The coefficient of sliding friction does not have any units and is valid only for the pair of surfaces in contact when the value is measured; any change in surface may cause the coefficient of sliding friction to change. You can measure force with a spring scale. The shoe did not accelerate horizontally was because of friction between the shoe and the surface . The force applied was equal to the frictional force. Pulling and frictional forces are equal in strength and the shoe did not move vertically. The perpendicular force to the surface is the normal force. The normal force is in the opposite direction of the shoe's weight. The coefficient of sliding friction is equal to the force of friction divided by normal force.
 * Physics Talk**
 * µ**
 * coefficient of friction
 * no units
 * ratio of friction force to normal force
 * measure of how much 2 surfaces interact when sliding
 * 0 < µ <1
 * µ bigger when surface is rough
 * independent of weight
 * only valid for a particular pair of surfaces

1. Their net force is zero because they are equal and the forces go opposite in direction.  2. It has no units because the N cancels out.  3. To find the coefficient of sliding friction is the equation is force of friction divided by normal force
 * Checking Up **

1. Baseball: when the field and clay are try, it is easier to run on and the ball bounces and moves farther. If the field is wet, the ball tends to not bounce and it is harder to run on the clay and grass. You have the chance at sinking and slipping on the clay. 2. People who wax their snowboards do this because it takes away some of the friction between the snow and the board. 3. No, she needs to be aware of the slipperiness of the floor. 4. Each surface is different and certain circumstances, different shoes are necessary. 5) .03 = F(f) / 600 N ∑Fy=may N-w=0 N=w=9800N
 * Physics Plus**
 * Physics To Go**
 * F(f) = 18 N **
 * 6.a) w=mg **
 * =(1000)(9.8) **
 * 9800 **
 * b) **

** f=mN ** ** =(.55)(9800) ** f=5390N

c) ∑Fx=ma -f=ma  -5390=1000a  -5.39 m/s2=a  No friction=no walking Fk max limits acceleration
 * 7. The forces of air and water resistance do change when speeds change. **
 * 8. When there is a maximum frictional force, there definitely is a limit on how fast you can start. If there is a maximum, then you cannot go above the maximum. Buying shoes with a much smoother sole will solve this problem. **
 * 10. Friction is important in running because friction allows you to push off of the ground and accelerate. Without friction you cannot accelerate. Baseball players wear cleats to move faster and have a better grip on the ground to make their accelerations higher. **

1) The friction between the surface and the block is the coefficient of friction 2) They should be close because they are on the same surface and all weigh relatively the same weight. Although I was 36% error, I feel as if my information demonstrates what happens to the block and how much the block weighs. 3) .04% off, .3% off, .26% off, high. 4) Yes because when certain things weigh different and they're on different surfaces, the friction will be higher. This related to shoes in different kinds of sports. 5) Slow reaction time, moving tape, and wrong measurement.
 * Investigate**
 * Questions:**

You need more friction in order to move faster or have better grip on whatever surface the sport is being played on. In baseball you need cleats because there is more friction which allows the person to get a better push before they run. They also won't slide on the clay or grass because of the grip from the shoe. In basketball you don't need the spikes on the shoes because the surface does not need a shoe that can dig into it to cause more friction. Basketball shoes have rubber on the bottom so there is still grip on the shoe so the person doesn't slide and so that they can get a grip before they accelerate to run. Cleats on a basketball court would destroy the surface and make running harder.
 * What do you think now?**

= Chapter 2, Section 8 =

The girl is trying to pole vault by running and sticking the pole in a given spot. The momentum seems to be bringing her up over the building on top of it. The pole bends and allows the girl to go around it and make it to the height of the building.
 * What do you see?**

You need enough weight on the pole to get you to go higher. If you get a longer pole, the person will not be able to get their body to even get the pole to go as high as they want to. It is harder for a short, light weight person to use the same length pole as a tall, heavier weight person. The speed, weight, and momentum of the person limit the height a pole vaulter has been able to attain. If the person runs fast enough and gains momentum then they will be able to farther up.
 * What do you think?**

a. The ruler is placed on the table with half of it off of the table. The penny is placed on top of the ruler where it hangs over the table. Then the ruler is bent as far as it can go without it breaking and the penny is launched up towards the ceiling. b. The ruler needs to be half off the table and the ruler has to be bent in order for the penny to be projected in the air.
 * Pre-Lab Activity**

//Factors that affect the height that the penny reaches:// -Deflection of the ruler (elasticity,force) -Length of ruler - half -Placement of object -Mass of object.

Relationship between **height** and **length of ruler**
 * Investigate**


 * **Centimeters off the table** || **How far penny is projected in air** || **Observations** ||
 * .5 cm || 46 cm || -after 2 trials the penny reached between 40 and 50 cm ||
 * 1.0 cm || 73 cm || -after 2 trials the penny reached between 70 and 75 cm ||
 * 1.5 cm || 126 cm || -after 2 trials the penny reached between 125 and 130 cm ||
 * 2.0 cm || 184 cm || -after 2 trials the penny reached between 180 and 189 cm ||
 * 2.5 cm || 197 cm || -after 2 trials the penny reached between 195 and 200 cm ||

perpendicular: work is 0 || //k// stands for spring force constant -How "springy" it is -low //k// values: slinkys (loose springs-easy to stretch) -high //k// values: spring boards (does not stretch easily (stiff)-takes a lot of force) x stands for the distance that is stretched or compressed
 * Physics Talk Summary**
 * Law of Conservation of Energy
 * the concept that the total amount of energy remains constant
 * When a force acts on an object, the speed and position of the object may change
 * May change in a way that makes the object go back to its original values
 * **kinetic energy:** energy associated with motion
 * **gravitational potential energy:** energy associated with position
 * **potential energy:** total of energy
 * when force acts on an object, the energy changes from one form to another but the sum of the potential and kinetic remains constant
 * Energy and Work
 * Conservation of energy in the pole vault
 * **Elastic Potential Energy**
 * As a pole or ruler straightens, it's elastic potential is transferred into the pole vaulter or the coin. (becoming kinetic)
 * Richard Feynman's Explanation of the Conservation of Energy
 * **Work Equation**
 * **W = F x d**
 * **Elastic (spring) potential energy**
 * **EPE = 1/2 kx(2)**
 * **Gravitational Potential Energy**
 * **GPE = mgh**
 * **Kinetic Energy**
 * **KE = 1/2 mv (2)**
 * ** Type of Energy ** || ** Description ** || ** Equation ** ||
 * Kinetic Energy || Energy possessed by an object when it is moving || KE=1/2mv(^2) ||
 * Gravitational Potential Energy || Energy possessed by an object when it is above it's lowest point || GPE=mgh ||
 * Elastic Potential Energy || energy possessed by a spring when stretched or compressed || EPE=1/2kx(^2) ||
 * Work || Caused by a force acting over some distance parallel to the direction of potion. Not really "energy" but it creates energy. || W=F*d
 * Notes for EPE:**

1) What is required for the energy of an object to change? **Force** 2) From where does the penny that is launched into the air get its energy? **The ruler** 3) From where does the pole vaulter get energy needed to bend the pole and then rise over the bar? **Kinetic energy from running** 4) What are the units for work, kinetic energy, gravitational potential energy and spring potential energy? **Joules**
 * Checking Up Questions**

1) Starts off with work (pushing), then gets height (kinetic) and **gravitational potential energy** then to kinetic energy cause it's following down and work when it lands. 2) For golf, when swinging, it's kinetic, it changes to work on the ball, then the ball has kinetic energy as its moving upward, then to gravitational potential energy, then to kinetic when its going downward then work when it lands. 3) 7.3 m 4) All poles have elastic potential energy which release the compressed energy into the person allowing them to go high and far regardless of the pole they use. **You need to know the initial velocity and the work done on the pole.** 5) The addition of heat makes your height increase because you have to put into account, the heat that is loss to the heat to equal the velocity. The potential is less **(100=100+2 X 100 = 98 +2)** 6) 7) His initial velocity needs to be higher. 8) a. b. You could do the calculations because the masses cancel in the equation anyway. This means that when friction is not considered, objects fall at the same speed. 9. a) **W = 374** b) EPE = KE 1/2kx^2=1/2mv^2 31 m/s =v 10. a) W = EPE =1/2kx^2 =1/2 (315) (.3)^2 = 14.2 J b) Fd = 1/2 kx^2 F(.3)=14.2 F=47.3 N 11. GPE = EPE mgh = 1/2kx^2 .04*9.8*1 =1/2(18)x x=.21 m 12. a) F=ma N = kg * m/s^2 b) GPE = mgh = (kg*(m/s^2)) *m =N*m c) KE = 1/2mv^2 kg(m/s)^2 kg (m^2/s^2)=N*m d) EPE = 1/2 kx^2 = N/m^2 *m^2 (m cancels, square cancels) =N*m 13. The spring is compressed (GPE), then kinetic to speed up to the highest point (GPE) then on the way down (kinetic) then water stops the diver. 14. Work is required to get ball in the air until it is released then when its moving in the air there is kinetic. 15.) The pitcher throws the ball towards the player (kinetic). . 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. 16.) The soccer ball rolls towards the player (kinetic). 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. While in the air it has kinetic energy.
 * Physics To Go**
 * W=EPE**
 * 1/2kx^x= 47 J**

**What do you think now?** The pole vaulter can't reach 12 m hight because of the initial velocity that is given and the work that is done on the pole. The GPE is the gravitational potential energy and stands for the object/person being above above ground has to be equal with the work done because of the law of conservation of energy. The amount of energy has to stay the same. If the mass is increased, then the work done will have to be increased as well.

= Chapter 2, Section 9 =

The boy on the ice is jumping and seems to be as high as the helicopter. The person in the helicopter is timing how long the ice skater is in the air.
 * What do you see?**

No, because the gravitational pull would bring them down. The athlete would need an extra push to be able to go higher than an average person can go. World class figure skaters do not defy gravity. They stay up in the air as long as they possibly can. This is long enough to land a triple axel. Most ice skaters cannot do a triple axel because they do not have the training a world class ice skater has.
 * What do you think?**

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. To show energy transformations, you can use a table. All energies must be equal. 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. There are many different energies that deal with heat as well like nuclear energy or light energy for example. They also follow the conservation of energies where they can't be created or destroyed, only equal. A specific object can lose or gain energy but the whole system must keep equal energy.
 * Physics Talk**

Checking Up Questions 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. This will turn into gravitational potential energy. 3.) Nuclear energy, sound energy, and light energy are all different types. They are energies due to heat.

1.) W= GPE FD= mgh W=50 (9.8)(1) W= 490 J 2.) Work (in from push) + GPE ---> Kinetic energy --> Work (out from break) 3.) In order to test this we would watch the video in slow motion. The person continues to move in a parabolic shape. **The center of their mass continuously moves.** 4.) The person might have evidence that it is true, but they are mistaken. The arguing person could explain that it looks like they are defying gravity because of how small their displacement is. You need an experiment that anyone can duplicate to prove that what you're saying is true. 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 6b.) W = FD W = 1 (10) = 10 J 6c.) W = 10 (1) W = 10 J 6d.) W = FD W = .10 (100) W = 10 J 6e.) W = FD W = 100 (.10) W = 10 J 7a.) GPE = 1 J 7b.) GPE = 10 J 7c.) GPE = 10 J 7d.) GPE = 10 J 7e.) GPE = 10 J 8a.) KE = 1 J 8b.) KE = 10 J 8c.) KE = 10 J 8d.) KE = 10 J 8e.) 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 = 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.)
 * Physics To Go**
 * || 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 ||

1) 2)
 * Active Physics Plus**

Athletes do not and cannot "defy gravity". They use the conservation of energy to get enough kinetic energy to keep them in the air long (triple axels). If a triple axel was put in slow motion, it could be seen that there is displacement in every frame. The athlete is able to stay in the air so long because they have enough kinetic energy to stay in the air. (The more kinetic energy, the longer time in the air)
 * What do you think now?**