1. Unit 4 Lecture
Chapter 15

2. Energy and Work Energy is the ability to do work
Energy is measured in Joules (J)
Two types:
1. Kinetic- movement
2. Potential- stored

3. Kinetic Energy Energy in motion Kinetic Energy = ½ x mass x velocity2
KE = ½ mv2
KE is in Joules
Mass is in kg
Velocity is in m/s

4. Practice Problems
What is the kinetic energy of a jogger with a mass of 65.0 kg traveling at a speed of 3m/s?
What is the kinetic energy of a 1 kg pie travelling at a speed of 4 m/s ?

5. Potential Energy 3 types:
1. Chemical- energy in bonds ex: food, atomic bomb
2. Elastic- energy in things that compress and stretch ex: rubberbands and springs
3. Gravitational- objects suspended above Earth

6. Gravitational Potential Energy
GPE= mass x gravity x height
GPE= m x g x h
GPE in Joules
Mass in kg
Gravity on Earth is 9.8 m/s2
Height in m

7. Practice Problems
Find the gravitational potential energy of a light that has a mass of 13.0 kg and is 4.8 m above the ground.
A cart at the top of a 300 m hill has a mass of  40 kg.  What is the cart’s gravitational potential energy?

8. Forms of Energy 1. Mechanical- motion and position, PE + KE
2. Thermal- particles, PE + KE
3. Chemical- chemical bonds and compounds
4. Electrical- electric charges
5. Electromagnetic- the EM Spectrum (radiation spectrum)
6. Nuclear- atomic bonds, atomic decay

9. Energy Conversions Mechanical Energy = PE + KE
(PE + KE)start = (PE + KE)end
Meteor falling and impact: KELightHeat
Wind up toys: PEKE
Lightbulbs: Elec ELight and Heat
Food: Chem PEKE + Heat
Falling Objects: GPEKE

10. Energy Conversions in a Pendelum

11. Law of Conservation of Energy
Law of Conservation of energy states:
Energy cannot be created or destroyed
Energy changes form

12. Theory of Relativity Energy = mass x speed of light2 E = m x c2
Energy in Joules
Mass in kg
Speed of light= 3.0 x 108 m/s

13. Nonrenewable Energy
Nonrenewable energy is in limited quantities because it takes millions of years to produce
Ex: fossil fuels (coal, oil, natural gas)
Ex: elements (Uranium, Plutonium)
People have the desire to become more efficient in order to reduce our usage.
Ex: energy star appliances, CFL lightbulbs, hybrid cars

14. Renewable Energy
Renewable energy can be replaced in a much shorter time than nonrenewable
4 types:
1. hydro- energy from flowing water ex: falling water turns turbines
2. solar- sunlight heats plates where water flows through, rising steam turns turbines

15. 3. Geothermal- water is pumped into heated underground spaces which creates steam, rising steam turns the turbines
4. Biomass- chemical potential energy is stored in plants, burned or converted into ethanol
5. Wind- turns large turbines