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toc 'Maurel Thom's Wikilog - Period 6 CP Physics - Burns - 2011

CHAPTER 2

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SECTION 8
What Do You See A pole vaulter is running with a high acceleration in order to clear a 20 foot wall.

What Do You Think Even though the poles are still close to the heights, there is still a .5 meter gap. What will work for one jump may not necessarily work for the other. Speed and weight limit the height that a pole vaulter is able to attain. Also, the length of the pole and flexibility.

Investigation Prelab Activity: a. The more you pull back, the higher the penny goes b The further off the table the ruler is, the further you can pull back - resulting in a higher altitude. How high above the ground the ruler is affects the maximum height you can achieve. The flexibility and material of the ruler also affect the height.

1a. Will the mass of a coin affect the height it can reach b) We will record the maximum height of a penny, dime, and then the maximum height of a nickel, three times each. c) We will use a meter stick to measure d) Making comparison between the three coins

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

Physics Talk Law of Conservation of Energy - the total energy of a system remains constant, although the TYPES of energy might change. A force can change the position and speed of an object in a way that allows the position and speed to change back Kinetic Energy - KE - energy something has because it is moving (KE = 1/2 mv^2) energy associated with motion. Elastic Energy - EPE - energy a spring has when stretched of compressed. (EPE = 1/2 kx^2) Gravitational Potential Energy - GPE - energy that something has to due to its location relative to the ground (GPE = mgh) energy an object has because of its vertical positon (must be in the air) from the Earth. Work - caused when a force is exerted over some distance parallel to the motion (W = Fxd) - the product of displacement and the force in the direction of the displacement

Checking Up 1. A change in energy can be caused by a force, like tension, normal, friction, or weight. 2. The penny gets its energy from a ruler that has elastic potential energy. The ruler transfers its energy to the penny, which transfers the energy through the air. 3. The vaulter's kinetic energy is used to catapult him with an initial speed upward and the remaining kinetic energy is turned into elastic potential energy as the pole bends. 4. The unit of energy is -J-, or Joules, named after the physicist.

What Do You Think Now SPEED is the main factor in the equation. Humans have a max speed that they can achieve, so one can only get so high. Mass does not necessarily matter as much. Flexibility of the pole is still a factor however. energy conservation. The amount of kinetic energy you exert is the same amount of potential energy that will result.

Physics to Go 1. In a shot put, you start of with Work energy because your arm exerting a push on the shot put. That energy is transferred into kinetic energy as the shot put travels through the air. GPE, or gravity, is acting on as it travels through the air until it hits the ground. EPE, or elastic energy, is not a factor. 2. When hitting a golf ball, the club exerts a push on the ball which gives the ball its initial energy. That push is work energy. That work is transferred into kinetic energy as it sails through the air while gravity acts on it. There are no rubber bands or strings so elastic potential energy is not a factor. 3. 1/2mv^2=mgh The masses cancel - 1/2v2 = gh Therefore, a vaulter such as Carl Lewis could go as high as his speed energy would take him. Speed (v^2) would be the main factor in determining his max height. 4. The main factors that limit max height are EPE, GPE, and speed/momentum. Your speed transfers your energy through the pole, which turns into EPE. GPE is also acting while you a catapulted through the air. So length of the pole is only a small part of the equation. 5. If the pole does not stretch as much as it normally would, that would limit the Elastic Potential Energy, which would disrupt the law of conservation of energy. 6. KE = GPE 1/2mv^2 = mgh 1/2v^2 = (9.8)4.55 v = 9.44 m/s

7. KE = GPE 1/2mv^2 = mgh 1/2v^2 = (9.8)6.14 v=10.97 m/s Sergei achieved a higher height, therefore, her speed was likely greater.

8a.) GPE = KE mgh = 1/2mv (9.8)(100) = 1/2v v = 1960 m/s b) You don't need the mass of the rock because it cancels out

9.) Wpullback = EPEf W = 1/2kx^2 W = 1/2(1500)(.25)^2 W = 46.875

b) EPE = KE 1/2kx^2 = 1/2mv^2 1/2(1500)(.25)^2 =1/2(.1)v^2 v=30.6 m/s

10. EPE = W 1/2kx^2 = F x d 1/2(315)(.3)^2= W 14.2 = W b) 14.2 = F x .3 47.3 N = F

11. GPE = EPE mgh = 1/2kx^2 .04(9.8)1=1/2(18)x^2 x = .21 12. F (measured in N)= m(measured in kg) x a(measured in m/s^2). Therefore 1N = 1kg x 1m/s^2 b) GPE=mgh ; (kg)(m/s^2) ; 1kg x 1 m/s^2 = J c) KE=1/2mv^2 ; 1/2(kg)(m/s)^2 ; 1kg x 1 m/s^2 = J d) EPE = 1/2kx^2 ; 1/2[(kg)(m/s^2)/m]m^2 cancels out to 1kg x 1 m/s^2 = J, the same way GPE = kx^2 does 13. EPE > KE > GPE > KE 14. In volleyball, the athlete does work with their arms/hand, resulting in KE, and GPE acts while the ball is in the air. 15. The bat exerts a crazy work force which sends seems to send an even crazier KE force through the ball, but in reality its the same amount of energy. Oh, but unfortunately, GPE eventually takes it out the sky. 16. A soccer ball has kinetic energy because it is increasing speed. The ball is kicked up due to kinetic energy and work. The kinetic energy transforms into gravitational energy at the peak of the balls height.

What Do You Think Now The most important factor is speed, not the length of the pole. The more speed and velocity you have, the more kinetic energy you will have when you are vaulting. Energy conservation allows the energy to shift through the pole and hurtle you over the wall.

SECTION 9
What Do You See An ice skater is twirling high in the air.

What Do You Think The hang time of athletes is determined by whatever they are doing, for example, a basketball players force on the ground to prepare for a jump or a skiiers speed when approaching a snow ramp. A world class figure skater maximizes his horizontal distance to ensure he gets the triple axel, he can only get so high on a vertical axis.

Investigation

__Prelab Activity__ Figure Skater Triple Axel 20 frames x 1/30s = 2/3 sec

Basketball dunk 31 frames x 1/30s ~=~ 1 sec

The athletes very very briefly 'hang' in the air during the moment of the maximum height.

1. 1st stage - Bent knees --> (Normal Force and Weight)(GPE and Work) 2nd stage - Unbent knees --> (Normal Force and Weight)(GPE and Work) 3rd stage - Off of floor --> (Weight)(GPE and KE)

2. You can conclude the force needed to jump to a certain height b) We will record the normal force (mass x gravity) c) We will use a scale and meter stick d)

Taylor's Mass in Kilograms = 79.38kg

Hips straight up - 117 cm knees bent - 86 cm heels in jump - 148 cm

4. Force = m(g) = 79.38(9.8) =777.924N

W=GPE F(d)=mgh F(36)= 65.77(9.8)(135) =2,800.5

Maurel's Mass in Kilograms = 65.77kg

hips standing - 99 cm hips when bent - 40 cm heels in jump - 135 cm

4. Force = m(g) = 65.77(9.8) =644.546N

W = GPE..... W = mgh. mg = 64.4kg (9.8). NF = 631.12N. GPE = mgh. GPE = 644.546 (.36). GPE = 232.03J... F x D = 232.03J. F(.15) = 227.2J... F = 1,514.67N Calculated Force: 1,514.67N 4) Actual Force: 1,420.67N

Calculated Force: 1,502.64 Maurel Actual Force: 1,456.17N

Calculated Force: 2,010.N Taylor Actual Force: 1,881.7N

Physics Talk Conservation of Energy - total energy remains the same. as energy moves throughout a system, there is no energy lost or gained. there are four types of energy. EPE - elastic potential energy - requires a rubber band or a stretched or compressed spring GPE - gravity - acts when something is off the ground Work - a push or pull - a force exerted when something is pushed or pulled over a distance KE - kinetic energy - energy resulting in movement. In a jump, your knees act as compressed springs that stretch. The EPE is transferred into vertical KE, and GPE acts on you at your max height, returning you to the ground, where your knees (which are like springs) once again compress.

Checking Up 1. The energy between ready and the launch position is elastic. It is mainly stored in the lower half of your body, more specifically, your knees. 2. On the ground you will have EPE. In the air you will have GPE and KE. 3. The other three types of energy are Elastic, Work, and Gravitational.

Physics Plus 1.GPE --> KE mgh = 1/2 mv^2 9.8(20) = 1/2v2 196 = 1/2v2 392 = v2 19.79mph = v

b) If its mass independent, the amount of passengers and the weight on the roller coaster will not affect the ride.

2. EPE --> KE 1/2kx^2 = 1/2mv^2 1/2(60)(.40m)^2 = 1/2(.3kg)v^2 5.9=v

3. GPE + W = KE = GPE mgh + (150,000) = mgh (9.8)(25) + 150,000 = (9.8)(h) h = 15,331.1 m

What Do You Think Now No, the hang time is just a "battle" between KE and GPE which results in arc that we call "hang" time. A ice skater maximizes his/her vertical AND horizontal distance to complete a triple axel. Conservation of energy always their KE on the ice to be transferred through the air, where GPE takes effect, ultimately returning the skater to the ground, where he/she will have the same amount of energy as the time he/she left the ground.

Physics to Go 1. 490J 2. During a bobsled run, you have; W +GPE --> KE --> Wout. Your final work is the result of your brakes. 3.Someone might only momentarily 'hang' in the air, but GPE is always in work, so when the person hits max height, they will immediately be brought back down. 4. If someone could defy the laws of physics, they wouldn't be laws. However, in the science world, someone should definitely have the opportunity to prove that it is not true. That is how scientists learn and advance. 5.increasing F - muscle strength or a decrease in M, but not strength 6. W=Fxd, Fxd = mgh a) 1 J b) 10J c) 10J d) 10J e) 10J 7. 1 J b) 10J c) 10J d) 10J e) 10J 8. 1 J b) 10J c) 10J d) 10J e) 10J

(Work for 6-8) W = Fd = (1)1 W =1 J b) W = Fd = (1)10 W=10 J c) W = Fd = (10)1 W =10 J d) W = Fd = (.1)100 W=10 J e) W = Fd = (100).1 W=10 J

9. 2,150J W = Fxd W = (50)(43)

10. 2,084 J KE=1/2mv^2 = 1/2(62)8.2^2 KE= 2084.4 J

11. 6m/s^2 a= F/m F=m(a) 30 N= (5 kg)(a)

12. 12.5m d = W/F W = Fxd 40,000 J = 3200(d) b) 563 J

13. 120J W=KE = 1/2mv^2 14.17m 15. The KE when RUNNING is 100J. GPE is 0. EPE is 0. total = 1000 The KE when the POLE IS FULLY BENT is 100. GPE is 0. EPE is 900. total = 1000 The KE at the PEAK HEIGHT 0. GPE is 1000. EPE is 0. total = 1000 The LANDING has 850 J of KE. GPE is 150. EPE is 0. total = 100 The KE during the CUSHION COLLAPSE is 0. GPE is 50. EPE is 0. total 0 because 950J of energy are worked out

16. The KE at the PEAK HEIGHT is 0. GPE is 1000. EPE is 0. total = 1000 The KE during the LANDING is 800. GPE is 200. EPE is 0. total = 1000J The KE at the LOWEST HEIGHT is 0. GPE is 0. EPE is 1000. total = 1000

17. TOP OF THE MOUTAIN is 0. GPE is 1000. EPE is 0. Total = 1000 The KE at the MIDDLE is 500. GPE is 500. EPE is 0. Total = 1000 The KE at the BOTTOM is 1000. GPE is 0. EPE is 0. total = 1000