Download Gravitational Potential Energy and Kinetic Energy

Gravitational
Potential Energy
and Kinetic Energy
SECTION 4.2
Patterns
 What
happened to the speed as the
height increased?
Graphs
Height v. Speed
2.5
Height v. Speed2
1.5
1
0.5
0
0
0.05
0.1
0.15
0.2
Height (m)
0.25
0.3
0.35
0.4
Speed2 (m 2 /s2 )
Speed (m/s)
2
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
0.05
0.1
0.15
0.2
Height (m)
0.25
0.3
0.35
0.4
What determines speed
at the bottom of the
incline? SPEED!
The Secret is in Energy
 Gravitational
Potential Energy – the
energy a body possesses as a result of
its position in a gravitational field; it is
dependent on height; GPE = mgh
 Kinetic energy – the energy an object
possesses because of its motion; it is
dependent on speed; KE = 1/2 mv2
Units
 Joule
– the SI unit for work and all
other forms of energy; one joule (1 J)
of work is done when a force of one
newton moves an object one meter
in the direction of force
Total Energy
GRAVITATIONAL POTENTIAL ENERGY + KINETIC
ENERGY = TOTAL ENERGY
 In a closed system, TOTAL ENERGY is constant
PRACTICE
 The
total energy of a system is 40,000
J. If the gravitational potential energy
is 30,000 J as the roller coaster starts
descending down a hill, how much
kinetic energy does it have?
PRACTICE
Mass of car = 300 kg and g = 10 m/s2
(approximately)
Position of car
GPE (J) = KE (J) = 1/2 GPE + KE
(height; m)
mgh
mv2
(J)
Top (25 m)
Bottom (0 m)
Halfway down
(10 m)
Three quarters of
What do you Think Now?
 Why
does the steeper slope provide
the bigger thrill?