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=Chris Marini's Wikilog= toc =Chapter 2=

What do you think?
Ice skaters are able to continue gliding across the ice without much effort because there is very little friction between the skates and the ice so they don't slow down very easily. A soccer ball continues to roll because once it gains momentum it wont stop until another force acts on it. An object that is in motion stays in motion unless another force acts upon it.

Sports Article http://www.curlingbasics.com/ This web site is about the art of curling. It talks about the strategies used to make the ball come as close to the target as possible. It talks about the sweepers sweep in front of the rock to reduce friction between the rock and the ice so it can travel farther. It says how most of the rocks are thrown with the same power, the sweepers are the ones that determine how far the rock will go. The thrower just aims the rock. A precise thrower is the best thrower.

Investigation 1

 * 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.  5.88
 * 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.  4.83 meters
 * 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.


 * 1) Predict where the skater will reach his highest position if he begins at the same place as before.  The skater will go higher because the slope is less.
 * 2) Explain why you think so.  If the slope is less it will take longer for it to slow down.
 * 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”?  My prediction was wrong because even though it took longer for the skater to stop, the slope was less so it took longr for it to get higher.
 * 3) 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.  Bother the heights are equal.
 * 4) Repeat Steps 2 and 3, creating an even less steep slope.
 * 5) First record your prediction.  The skater will continue going the same height.
 * 6) Compare your prediction with the outcome.  The skater continued to reach the same height.
 * 7) Imagine what would happen if you changed the right-hand section of the track so that it would be horizontal (zero slope).
 * 8) No matter how far along the horizontal track the skater rolls, would he ever recover his starting height?  No, because there is no slope so the skater gains no height.
 * 9) How far do you think the skater would roll?  The skater will roll until a separate force acts on him, until friction causes it to stop.
 * 10) What would keep the skater rolling on a horizontal track?  A lack of friction
 * 11) Try this on the simulation. What happens?  The skater continues to roll until the track ends.
 * 12) Conclusion Questions:
 * 13) What happens to the length of the opposite track the skater rides as the slope decreases?  You have to make the track longer because the slope isn't as steep so it takes longer for the skater to stop.
 * 14) What happens to the final vertical position on the opposite track the skater rides as the slope decreases?  It stays the same as the original height.
 * 15) 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?  They end at the same height that they get released because the momentum stays the same and there is no friction to slow it down.
 * 16) If the opposite track was infinitely long, and frictionless, when would the skater stop?  It would never stop.

Physics Talk
An object at rest stays at rest unless a force acts upon it. (inertia) Inertia is a property of matter that measures the resistance to change an objects motion. It is the natural tendency of an object to remain at rest r to remain moving with a constant speed. Without an unbalanced force, an object will remain at rest. If an object is already in motion it will keep a constant speed.

Checking up questions 1) Inertia is the natural tendency of an object to remain at rest or to remain moving at a constant speed. 2) The speed of an object in motion will remain ocnstant and an object that is at rest will stay at rest unless there is inertia. 3) In order for an object to stop moving an unbalenced forec would have to act upon it. 4) The force that would make a ball stop would be friction. 5) The more the mass the greater the inertia. 6) The speed of the ball is constant with the train.

Physics to go 1)a) the ball will roll forever unless an unbalanced force acts on it. b) Newtons first law of motion says that an object that is at rest stays at rest and an object in motion remains in motion with a constant speed. 2) The same height of 20cm. 3) Yes because if there is no force acting on it and nothing in the way it will by theory continue moving forever. 4) A hockey pucl slides across the ice for a long time because there is not a lot of friction acting on. 5) 2.5+4.5= 7m/s 6) 10.3+4.2= 14.5m/s 7)a) 5.6+2.4= 8m/s b) 5.6-2.4= 3.2m/s c) 8) 67 m/s

Inquiring Further

What do you think now? It is easier for ice skaters to move across the ice compared to someone else because there is less friction on ice, therefor harder to stop. There is always friction present or else the person or ball or whatever would keep moving forever.

=Section 2= What do you think? In this picture there is a kid walking behind a dog. You can see that they are walking slow because the footprints are close together. Both measurements describe the velocity at witch a pitcher throws the ball. It effects how much time the hiter has to react to the ball.

Physics Talk:
Instantaneous speed is how fast you are going at a given moment, Average velocity is the overall speed of an object over a given amount of time, Average speed is distance traveled divided by the time it took to travel.

Checking up:
1)a) The distance between the dots should be exactly the same when the speed is constant. b) Disance between thte dots should increase as the acceleration increases. c) As the acceleration becomes negative the dots should become closer together. 2)400/50=8.... V=8m/s 3) Average speed is all the speeds during a trip averaged together to get one speed, instantaneous speed is just one speed. 4)100/10= 10... a=10 m/s

Physics to go:
1) Instantaneous speed is one speed throughout a trip, average speed is total distance over total time. 2)a) 1000/15= 66.7...v=66.7m/s b)84/6=14... v=14m/s c)9.6/2=4.8...v=4.8m/s d)400/4.5=88.9...v=88.9m/s 3)a) Positive b) Positive c) No d) No e) No f) No 4)a) graph A and D b) Graph B c) Graph A d) None e) None, Increase then decrease, Increase. 6)a) 12.5/9=1.36...a=1.36m/s^2 b) The speed was decreased, therefore it is negative. 7)a) Constant b) Acceleration c) Constant, accelerarion, negative acceleration. d) constant, negative acceleration, acceleration 8)100/2=50... v=50m/s 9)Not necessarily because instantaneous and average speed are two completely different thing, if they were ever the same it would be by coincidence. 10) [] [] [] [] [] [] [] 14)a) A car driving on the highway with no traffic. b) A football player sprinting the 40 yard dash. c) A car driving in a lot of traffic. d) A quarterback throwing a pass. e) A car coming to a complete stop after going fast.

What do you think now?
Now i know that there are different things you hae to take into account. These speeds could be average speeds, or instantaneous speeds. Instantaneous speed is one certain speed and average speed are many speeds averaged together.

=Section 3=

What do you think?
A force is something that causes an object to do something. Yes, if you inflicted the same amount of force onto a tennis ball and a bowling ball, the tennis ball would be effected more.

Physics Talk:
Newtons 2nd law is acceleration = force over mass. Unbalanced force causes acceleration. The smaller the mass, the less force needed to move it. Gravity causes weight. Net force is the combination of all forces on an object. Net force is directly proportional to acceleration.

Checking up:
1) Newtons second law says that if there is no unbalanced force acting on an object, then the object will not accelerate. 2) If the object has a larger mass then the acceleration will be less. 3) It would mean that if you multiplied the force of gravity times the mass, you would get 30. 4) On a planet with higher acceleration, your weight and mass would both be less because as mass goes down, acceleration goes up.

Physics To Go:


=Section 4=

What do you think?
The girl is dropping red and green apple. She is dropping the green apples at a projection and the red apples straight down. There is a boy timing how long it takes for the apples to hit the ground. I think that how hard you throw the ball and what angle you throw it at. Other things that help determine how far it goes is the weight of the object.

Physics Talk
The trajectory of an item is the path it takes. Horizontal Distance= x Vertical distance= y Horizontal velocity does not change while vertical velocity changes by -9.8 m/s.

Checking up questions:
1) Yes, because unless there is air resistance they will fall at the same rate. 2) Its velocity increases as it continues to fall down by 9.8m/s. 3) At its highest point the acceleration is 0 because at its highest point it is not accelerating up and also has not yet began to accelerate down. The acceleration of the ball is constant at -9.8m/s^2.

Physics To go:
What do you think now? I now think that gravitational pull helps determine how far an object goes. -9.8m/s^2 acting on an object. Also without air resistance objects will fall at the same speed.

=Section 5=

What do you think?
The girl kicks a soccer ball to her teammate who redirects the ball with his head past the goalie into the net. The range is changed because the angle and the velocity of the ball changes after the boy hits the soccer ball at a different angle.

Physics Talk
Constant speed and downward acceleration are the two motions that make up a projectile. All balls travel in parabolas. The smaller the angle the greater the horizontal velocity.

Checking up questions
1) Constant speed and downward acceleration. 2) The fundamental requirements are for the model to match reality in nature. 3) All distances that add up to 90 degrees go the same distance no matter what.

Physics To Go
1) A 45 degree angle will force the object to go the farthest it could possibly go because it is between 0 and 90 degrees. 2) When the angle is is greater than 45 degrees the object will travel a less distance. 3)a) 60 degrees. b) 75 degrees. 4) Because the jumpers don't have the ability to jump at a 45 degree angle. 5) Because he was able to use his speed from sprinting and combine it with his jumping ability. Since he was running at a really fast speed and could jump higher than other contestants he was in the air for a longer time and also had a faster horizontal velocity. 6)a) Downward. b)Horizontal 7), 8), 9)

What do you think now?
If you project an object at a 45 degree angle it will go the farthest it can possibly travel. From 1 degree to 45 degrees the distance the object will go farther as the angle increases, as the angle continues to increase from 46 degrees to 90 degrees the distance becomes less and less.

=Section 6=

What do you think?
There is a kid in a wheel chair with his feet pressed up against the wall. It seems like he pushed of the wall with his feet and is now rolling backwards. I would tell them to bend their knees and then press off directly perpendicular with the ground to cause them to go up.

Physics Talk
Newtons 3rd law says that for every force applied, there is an equal and opposite force. The opposite force happens instantaneously. A free body diagram is a diagram that shows the forces acting on an object in a given solution, every force is represented by an arrow, the strength is determined by the length of the arrow. The arrows are labeled with the type of force (N,W,F,T)

Checking up questions
1) For every force applied, there is an equal an opposite force. 2) Your body is the opposite force. 3) It shows witch type of force acts on witch object.

Physics to go:
1) Yes it does according to Newtons First law. 2) The natural force pushing up on the chair from the ground causes the equal force. 3) A bathroom scale works by a string pulling the spring. The more weight pulling on it the more newtons the object weighs. 4) The forces are equal. Bats sometimes break because the ball may hit the bat on an angle that causes the bat to break. 5) The force between the large line backer and small runnig back are equal when they make contact. It is much easier for the bigger linebacker to tackle the smaller running back because he has more mass. 6) The hockey player expresses force on the boards but the boards are also pushing back at the hockey player because there is an equal and opposite force. 7) The faster the ball goes, the more force is needed to make it stop. A glove provides cushion from the force of the ball on your hand and it makes it so there is less force applied back toward the ball so it doesnt just bounce right off your hand.

What do you think now?
I would tell them to apply the force straight down into the ground. When you do this the floor pushes an equal force back at you and you go up into the air.

=Section 7=

What do you think?
The boy is pulling the shoe very easily on the ice because there is no friction. On the other side of the picture the same boy is struggling to pull the shoe because there is a lot of friction. Some sports require certain shoes because in some sports you need more traction because the field you play on provides less friction. If the field you play on is slippery, i

Physics talk
Friction is a force that resists relative motion. It is present between objects when they make contact. The pulling force is equal to the frictional force so the net force is 0 because they are going in different directions. The force of friction is equal tot he force required to slide an object on the surface with a constant speed.

Checkin up questions
1) Newtons second law states that the force pulling a shoe and the friction thats stopping it are at constant speed witch proves that forces act in opposite directions and are equal. 2) Because there are two forces being divided by each other. 3) f/N= Mù

Physics to go 1) In basketball if the court is dusty it makes it more slippery and harder to start and stop. When this happens players usually wipe the bottom of their shoes to get rid of the dust so it is easier to stop (there is more friction) 2) In skiing or snow boarding the riders want to have the least amount of friction possible. they often wax theri boards so there will be less friction and they will move at the highest speed possible. 3) No, she cant be sure because the other court could be more dusty. Also the home court she is used to could have a better wax job and there could be more friction on the home court than the away court. 4) On different surfaces there are different amounts of friction so they need different shoes to match witchever court they are playing on. 5) .03=f/600 f= 18N 6)a) 100(9.8)= 980 b) n=w, u=f/N .55= f/980 f=539N c) f=ma 539=100a, a= 5.39 m/s^2 7) If you are moving at a constant speed the air resistance and water resistance are the same. There will be the most air resistance and water resistance when you are moving faster. 8) If there is a lot of friction it is easier to start. People accelerate at different speeds because they apply more force than others. 10) Friction is important in running because you need a lot of friction to start off. In other sports like football and soccer you wear cleats so you dont just slide off the turf, instead the cleats dig into the ground. 11)

What do you think now?
Some sports require different types of shoes because in the sports where you need to push off the ground and accelerate as fast as possible you need your shoe to create the most friction possible. If you wore shoes that caused very little friction with the ground you would not be able to push off and go as fast as if you wore a shoe that caused a lot of friction with the ground.

Reflection
=Section 8=

What do you see/ think?
Kids are running and trying to get enough speed to pole vault themselves over a very high wall and get into a party. They cant get over with a longer pole because it is more flimsy and harder t launch yourself high enough to get over the wall.

Investigate
Pre lab: a) Bend the ruler as much as possible. b) The less ruler that is sticking out the higher the penny is launched.

1)a) We will be able to conclude where the penny needs to be positioned in order to get the maximum height. b) Where the penny is positioned. Along with the constant force being used. And also the height the penny travels. c) We will use a meter stick and a ruler. d) We will look at how the height of the penny changes as we position it in different spots on the ruler and see whether the hight gets taller or shorter as we move closer to the table.

Trials:
 * Force || Ruler sticking Out || Position of Penny || Height of Penny ||
 * 2 cm || 11 cm || 2 cm out || 24 cm ||
 * 2 cm || 11 cm || 5 cm out || 33 cm ||
 * 2 cm || 11 cm || 7 cm out || 49 cm ||

Conclusion: The farther away the penny was placed from the table on the ruler, the higher the penny traveled throughout the air.

Physics Talk
There are 3 different types of energy, kinetic (energy an object has because of motion) KE=1/2mv^2, elastic potential energy (the energy a spring has when being stretched or compressed) EPE=1/2kx^2 (k=spring force constant), Gravitational potential energy (energy an object has due to its location relative to the ground) GPE= mgh. Work is caused when a force is exerted over some distance parallel to the motion, W=Fd.

Physics to go
1) There is GPE on the shot put ball followed by Work. Then there is Kinetic energy witch is the ball going through the air. 2) There is GPE when the golfball is sitting on the tee followed by work. Then Kinetic Energy when the ball moves through the air. 4) The lenght of the pole doesnt effect the height the pole vaulter travels. The velocity and work of the vaulter is most important. 5) The temperature does not effect what the vaulter does at all. 15) When the bat makes contact with the ball the ball takes off. This is Kinetic energy. As the ball starts falling towards the ground GPE acts on it and then Kinetic energy again as it bounces off the ground. 16) As the kid shoots the basketball up into the air, they are doing work witch forces the ball up into the air. As it travels through the air this is an example of kinetic energy. As the ball reaches travels through the air GPE is also acting on it because it is higher than the ground. Once the ball hits the ground and stops moving, there is work between the floor and the ball.

Checking up questions
1) A change in force causes an objects energy to change. 2) The penny's force comes from the force that is bending the ruler and the ruler slinging the penny into the air. 3) The speed of the vaulter decides whether he will make it over the bar. Also the bend of the pole and the force thrusts him over the bar. 4) It is measured in Jules.

What do you think now?
Because it doesn't matter what the length of the pole is, all that matters is the speed that you are moving with the pole. The faster you move the higher the amount of Kinetic energy is and therefore the GPE will be higher.

=Section 9=

What do you think?
The ice skater is jumping extremely high while the person in the helicopter next to her is holding a stop witch and timing her "hang time". It is impossible to defy the law of gravity, the ice skater is just moving fast so it looks like she is floating for a little while when really she is going up until she reaches a max height and then back down.

Investigate 9:
Prelab: 2. 20 frames 3. 2/3 of a second is the time that the person is in the air 4. In the middle of the jump, the skater "hung" for about 4 or 5 frames. It doesn't look like he is changing position because the change in position at those points is very small, it is just less noticeable 5. Basketball player: He is in the air for 31 frames, this includes when he is hanging onto the hoop. It is about one second. Lab: 1. First you bend your knees to get ready to jump, like your coil. Then you unbend your knees while your feet are still against the floor. In between those two motions you are pushing off the floor. You are then airborne and in the hair for some amount of time. In between those two there is gravity acting on you. Pushing: stage A, gravity: stage B W (unbending legs)=GPE (final) 5) My calculation was a lot higher than the measurement. Conclusion: My error occurred when i jumped on the scale. I did not jump as high as when we did it off of the ground.

Physics Talk:
Law of conservation of energy is total of all energies at any one time must equal the total of all energies at any other time. No matter what is lost or gained.

Checking up
1) A jumper gets ready to jump with Work. The bend in the legs and the pushing upwards against the ground is work. 2) In launch position there is work, at the maximum height there is GPE. 3) Light energy, chemical energy, and sound energy are three different types of energy.

Physics To Go
1) W=GPE W=mgh W=50(9.8)(1) W=490J 2) As the bobsledders are running there is W. After they stop pushing there is Kinetic energy as they are going down the course and also GPE. When they finally reach the bottom and come to a complete stop there is W caused by the choppy snoy that slows the sled, 3) i would tell them that it is impossible to hang in the air. You could draw lines at the waist of the jumper on the video and see that at no point is the jumper actually hanging in the air. 4) Impossible, then it wouldn't be a law, would it. 5) An athlete can jump higher by exerting a greater amount of Work between their legs and the ground and pumping their arms. 16) running(KE) bend(EPE) Max height(GPE) Landing(KE) 17) 18) The quarterback drops back to pass and throws the ball high into the air towards the endzone. There had to have been a lot of Work done by the quarterback because the ball is traveling so far. There is kinetic energy as the ball flies towards the endzone. And at its max height GPE takes over and finally the receiver catches the pass for a touchdown. The receiver used work to stop the ball and keep it secure. Physics Plus

What do you think now?
When you take the time to draw lines throughout the jump it is clear that the athlete is not hanging in the air and defying gravity. There is always a change in height, you just have to look closely enough.