Potential and Kinetic Energy…
• kinetic energy: is the energy which an object possesses due to its motion
• Potential energy: energy stored in a system because of its position.
http://www.youtube.com/watch?v=qZ4FFWvZtyo
Potential Energy
• Potential Energy is it has the ability to do work because of position or state.
• The energy of an object due to its position above the surface of the Earth.
Ep = W Potential energy equal to work done!
Ep = Fd
Gravitational Potential Energy
pE mghhttp://www.youtube.com/watch?v=DMrnAcnsvKY
Example
• Change in gravitational potential energy depends only on change in vertical height.
Elastic Potential Energy• The energy from a spring being altered from
its standard shape.
k: spring constantx: distance spring is stretched or compressed.
21
2pE kx
http://www.youtube.com/watch?v=Jnj8mc04r9E
Example 2An apple of mass 0.10 kg is suspended from a vertical
spring with spring constant 9.6 N/m. How much elastic potential energy is stored in the spring if the apple stretches the spring 20.4 cm?
?
:
204.0
6.9
:
e
mN
E
Unknown
mx
k
Givens
Example 2
An apple of mass 0.10 kg is suspended from a vertical spring with spring constant 9.6 N/m. How much elastic potential energy is stored in the spring if the apple stretches the spring 20.4 cm?
?
:
204.0
6.9
:
e
mN
E
Unknown
mx
k
Givens JE
mESolve
kxESelect
e
mN
e
e
20.0
204.06.9:
:2
21
221
Example 2
An apple of mass 0.10 kg is suspended from a vertical spring with spring constant 9.6 N/m. How much elastic potential energy is stored in the spring if the apple stretches the spring 20.4 cm?
?
:
204.0
6.9
:
e
mN
E
Unknown
mx
k
Givens
JE
mESolve
kxESelect
e
mN
e
e
20.0
204.06.9:
:2
21
221
Example 2 Follow-Up
How much gravitational potential energy did the apple lose?
Example 2 Follow-Up
How much gravitational potential energy did the apple lose?
?
:
204.0
8.9
10.0
:
2
g
sm
E
Unknown
mh
g
kgm
Givens
Example 2 Follow-Up
How much gravitational potential energy did the apple lose?
?
:
204.0
8.9
10.0
:
2
g
sm
E
Unknown
mh
g
kgm
Givens
JE
mkgESolve
hmgESelect
g
sm
g
g
20.0
204.08.910.0:
:
2
Example 2 Follow-Up
How much gravitational potential energy did the apple lose?
?
:
204.0
8.9
10.0
:
2
g
sm
E
Unknown
mh
g
kgm
Givens
JE
mkgESolve
hmgESelect
g
sm
g
g
20.0
204.08.910.0:
:
2
• Pg. 178– # 1-9
Kinetic Energy
21
2kE mv
• The energy due to the motion of an object• A scalar quantity
http://www.youtube.com/watch?v=BGmUVoX5s58
begin at 43sec
• A 0.300kg ball is pushed horizontally at a velocity of 20.0 m/s N. What the Ek of the ball as it moves?
• The kinetic energy of a moving object is 950 J as it moves 14.2 m/s. What is its mass?
Example 6.5
• On a highway, a car with mass of 1200kg and a Ek of 2500 J. What must the velocity of the car be?
Practice
• Pg. 179– # 4-5
• Pg. 181– # 6-7
• Pg. 182– #1-3, 5-7,