1. Energy Chapter 4

2. Work
Work –the transfer of energy that occurs when a force makes an object move.
The force and motion MUST be in same direction

3. WORK Work = Force X distance W=Fxd Units- Work: Joules (J)
Force: Newtons
Distance: m, cm, km

4. Energy Energy – the ability to do work or cause a change.
What types of energy can you think of?

5. Two main types of Energy Kinetic Energy: Energy of motion
Potential Energy: Stored energy
This depends on the position or shape of an object.

6. Kinetic Energy:
The amount of kinetic energy depends on the mass and velocity of the object.

7. Kinetic Energy Kinetic Energy = Mass x Velocity2 2 Units –
KE = ½ mv2
Units –
KE: Joules, J
v2: m2/s2
m: kg

8. Potential Energy:
Elastic Potential Energy- stored in something that can stretch or compress (rubber, springs, etc.)

9. Potential Energy:
Chemical Potential Energy- This is energy “stored” from chemical bonds.
Stored in the bonds and released when the bonds are broken.
Energy from a molecule of natural gas- when it burns the bonds break between hydrogen and carbon energy is released
Food – break down of glucose
Batteries

10. Potential Energy:
Gravitational Potential Energy- stored by objects that are above the Earth’s surface.
Depends on height above the ground AND
Mass

11. Gravitational Potential Energy
GPE = mass X gravity X height
GPE = m(10.0 m/s2)h or mgh
Units-
GPE: Joules (J)
mass: kg

12. The Formulas Work Kinetic Energy (KE)
Gravitation Potential Energy (GPE)

13. WORK Practice Problem
A cart was pushed 5 m across the floor with a force of 20N. How much work was done?

14. WORK Practice Problem use units, show work
A cart was pushed 5 m across the floor with a force of 20N. How much work was done?
W= Force x Distance
W= 20N x 5m
W= 100J

15. Kinetic Energy Practice Problem use units, show work
What is the Kinetic Energy (in Joules) of an object with a mass of 10 kg and a velocity of 10 m/s?

16. Kinetic Energy Practice Problem use units, show work
What is the Kinetic Energy (in Joules) of an object with a mass of 10 kg and a velocity of 10 m/s?
KE= ½ (10kg x (10m/s)2)
KE= ½ (10kg x 100m2/s2)
KE= ½ (1000J)
KE= 500J

17. Kinetic Energy Practice Problem use units, show work
When mass is doubled, what happens to KE?
When velocity is doubled, what happens to KE?

18. Kinetic Energy Practice Problem use units, show work
When mass is doubled, what happens to KE?
1,000J
When velocity is doubled, what happens to KE?
2,000J

19. Gravitational Potential Energy Practice Problem use units, show work
A 3kg cat is 4m up a tree. What is the cat’s GPE?

20. Gravitational Potential Energy Practice Problem use units, show work
A 3kg cat is 4m up a tree. What is the cat’s GPE?
117.6 J