Ch. 4 – Energy
I. Energy: The ability to cause a change!
A. Kinetic Energy: Energy in the form of motion
1. The amount of energy depends on the mass and the velocity
2. Equation: KE = ½ mv2
3. The SI units for any basic form of energy are Joules !!!
4. Example: An object with a mass of 10 kg moving at 5 m/s…
a. KE = ½ mv2
b. m = 10 kg v = 5 m/s
c. KE = ½ 10 (5)2
d. KE = 125 Joules
B. Potential Energy: Energy that is stored
(3 types)
1. Elastic Potential Energy:
Energy stored by stretching or compressing
2. Chemical Potential Energy: Energy stored in chemical bonds
3. Gravitational Potential Energy (GPE):
Energy stored due to height above the Earth
a. Amount of GPE depends on mass, amount of gravity and height
b. GPE = mgh –or- Wh (SI units = Joules)
c. Example: An object with a mass of 10 kg at a height of 15 m
on Earth (g = 9.8 m/s2)
1. GPE = mgh
3. GPE = 10 (15) (9.8)
2. M = 10 kg, h = 15 m, g = 9.8
4. GPE = 1470 Joules
II. Conservation of Energy
A. Energy Conversions: Energy is constantly changing from one
form to another.
1. Chemical Potential Energy: Fuels are this form (gas, food, etc.)
2. Mechanical Energy: Total KE and PE in a system
B. Law of Conservation of Energy: Energy may change form, but
Can never be lost or gained
(total never changes)
1. A swing set: switches between KE to PE and back
2. Swings don’t go forever because mechanical energy gets
changed into heat from friction (thermal energy), it isn’t lost
C. Nuclear Energy: Converting mass into energy
1. Nuclear Fusion: Smaller particles being forced together and
releasing large amounts of energy (stars, sun)
2. Nuclear Fission: Breaking down large particles into smaller
particles, releasing large amounts of energy
(nuclear warheads, power plants)
D. Converting energy in your body
1. Your body converts Chemical PE from your food
into the energy you need to function everyday.
2. The Calorie is the unit that food energy is
measured. One Calorie = 4180 Joules.
3. Example: A candy bar has 200 calories, how many Joules?
a. 1 Cal = 4180 J
b. Candy Bar = 200 Cal
c. 200 x 4180 = Joules
d. Candy Bar = 836,000 J