Section+8

=__//**Section 8- Potential and Kinetic Energy: Energy in the pole vault**//__= toc

What do you see?
page 220 1/14/11

A guy is mid pole vaulting over a building with people cheering and making noises on the roof. The person had to gain a lot of speed first.

What do you think?
page 220 1/14/11

Because the pole is now 1m less instead of .5m and it is harder to get the force to push you up so high. Weight, speed, length of pole, how much pole can bend

Investigate
page 220 1/14/11

1a. The ruler is pushed down with a penny on it and because of the restoring force the ruler drives up and the penny hits the ceiling. It is similar to the idea of a diving board. b. the harder you push down the higher in the air the penny goes. 5a. The farther it was from zero the farther it was dropped. 8a. The ruler increased more and more and the penny went higher and higher.

Class Notes
1/18/10

work= product of force on an object and the distance the object moves because of this force. W= F*D ex: A 25 kg object is lifted- how much work is done on the object if we lift it 1.5 m? W= (25*9.8)*1.5 W= 368 Joules

A joules is a measure of work and a measure of energy. This means that work and energy are equivalent. energy is used to do work.

Physics Talk
page 222 1/18/10

kinetic energy- energy associated with motion ke=1/2mv^2 v= velocity gravitational potential energy- the energy an object possesses because of its vertical position from Earth gpe=mgh potential energy- energy associated with position law of conservation of energy- energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant work- the product of the displacement and the force in the direction of the displacement work=f x d elastic potential energy (spring energy)- the energy of a spring due to its compression or stretch epe=1/2 kx^2 x= the compressing/ stretching k= spring constant

w=f*D work is done by a force whose direction is in the same direction as the motion

Checking Up
page 227 1/18/10

1. a force 2. potential gravitational 3. the run 4. joules

Physics Plus
page 228 1/18/10

For work, the distance must be in the same direction as the force.

Fs=KX force of a spring EPE+.5kx^2

b) the spring gives the toy KE which then give it the GPE EPE-KE-GPE

i do the work on spring which gives the spring joulses

KE=.5mv^2 KE= GPE .5mv^2=1.18 J

.5(100)v^2=1.18J v= 4.9 m/s

c) x= 2cm

EPE= .5kx^2 KE came from the EPE EPE=KE=1.18 J .5kx^2=1.18j .5k(.02)^2=1.18 J K= 5900 n/m

Physics To Go
page 232 1/21/11

1. doing work to pick it up and gravitational potential energy is there and more work to throw it farther. 2. 3. 7.35 m 4.the mass and spring constant also matter 5. energy is converted into heat and it is breaking over time 6. v= 9.4 m/s 7. v= 10 8. a. v= 44 m/s b. 9a. 47j b. 31 m/s 10a. 14 j b. 94.5 N 11. .2m 12. 13. using kinetic energy to bend board with gpe then bounces with ke then epe then back to ke then back to gpe and then ke. 14.