1. Energy

2. Energy is defined as the ability to do work.
Definition
Energy is defined as the ability to do work.

3. Some Types of Energy Mechanical Thermal Chemical Electrical
Mechanical energy is energy an object gains because work is done on it, thermal energy is heat energy, chemical energy is energy that is stored due to the properties of chemicals and electrical energy is energy associated with electricity.

4. Mechanical Energy Two major types: Kinetic Energy Potential Energy
Kinetic energy is the energy associated with moving objects. Potential energy is the energy due to an object’s position.

5. Kinetic Energy
KE = ½ mv2
Kinetic energy is calculated by the equation above: KE is the kinetic energy, m is the mass of the object and v is the speed of the object.

6. What is the kinetic energy of a 1000 kg car that is moving at 10 m/s?

7. Gravitational Potential Energy
PEg = mgh
Gravitational potential energy is the energy due to an object’s position relative to the Earth. PEg is the gravitational potential energy, m is the mass of the object, g is the local acceleration due to gravity (9.8 m/s2 for Earth) and h is the height above the “zero level”. h m

8. What is the potential energy of a 100 kg box that is 10 m off the ground?

9. Zero Level 10 kg 15 10 5 PEg= 0J PEg= 10kg(9.8 m/s2)(5m)=490J
Gravitational potential energy is measured relative to some arbitrary level. This level is the “zero level” and the height is measured from it. Thus all the values of PE above are correct, when using the corresponding colored line as the zero level.
PEg= 10kg(9.8 m/s2)(10m)=980J 5
PEg= 10kg(9.8 m/s2)(15m)=1470J

10. Elastic Potential Energy
PEelastic = ½ kx2 d2
A compressed or stretched material that is elastic (meaning it will return to its original shape) can have potential energy stored in it. This is elastic potential energy. In the equation k is the spring constant of the material and x is the distance the material is stretched or compressed from its unstressed length.
x = d2 – d1 d1

11. Total Mechanical Energy
TE = KE + PEg + PEelastic
The total mechanical energy of an object is the sum of the kinetic and potential energies.

12. W = DTE Work – Energy Theorem
The work energy theorem states that any work done by an external non-conservative force will change an object’s total energy. Non-conservative forces are most external forces other than gravity.

13. Conservation of Energy
Energy is always conserved. It cannot be created or destroyed. It can be changed from one form to another and/or transferred from one object to another, but the total amount of energy must remain the same.

14. Mechanical Energy Conservation
If W=0
then TE= constant
If no work is done on an object by an external non-conservative force, then the total mechanical energy of the object remains constant.