1. Chapter 13
WORK & ENERGY

2. TN Standards
CLE – Demonstrate the relationship among work, power, and machines
CLE – Investigate the Law of Conservation of Energy

3. Bellwork
What is Work?

4. Work, Power, and Machines
Work is conducted only when an applied ( net ) force results in the change in position of an object
Work is measured in Joules ( J )
Work is calculated by multiplying force and distance ( over which the force is applied )
W = F x d

5. Work, Power, and Machines
Power is the amount of work conducted over a certain time interval
P = W / Δt
Power is measured in Watts

6. Work, Power, and Machines
Machines help to do work by changing the size of an input force, the direction of a force, or both
Different forces can do the same amount of work
Figure 3 ( a box lifted vs a box pushed up a ramp )

7. Simple Machines The six types of simple machines are: Simple lever
Wheel and axle
Pulley
Simple inclined plane
Wedge
Screw

8. Compound Machines A combination of any of those six simple machines
Example – SCISSORS
Combination of lever and wedge

9. Bellwork
What is Energy?

10. What is Energy?
Energy is a property of an object due to its motion or its position
When work is done, energy is transferred or transformed from one system to another
Carry a tennis ball up in the stadium
You add potential energy to it by carrying it up

11. What is Energy? Energy is measured also in Joules ( J )
Potential energy – energy of position
PE = hmg
h is height ; g is gravity; m is mass
Height is relative
Kinetic Energy – energy of motion
KE = ( ½ ) mv2
m is mass ; v is velocity

12. Other Forms of Energy Mechanical energy Non-mechanical energy
( atomic level )
Chemical reactions involves chemical energy ( a form of potential energy )
Sun gets energy from nuclear reactions
Electrical energy ( stored in electric fields )

13. Conservation of Energy
Energy easily changes from one form to another ( battery )
PE can become KE ( tennis ball dropped from the top of stadium )
Vice-versa ( projectile shot / reaches max height )
Law of Conservation of Energy?
( neither created nor destroyed )

14. Roller Coaster Example

15. Thermodynamics
For any system, the net change in energy equals the energy transferred as work and heat
Efficiency ( how much energy/work you get out of a machine or process compared to how much is put in )
Internal Combustion Engine