1. Notes on Chapter 8 Work & Energy
Conceptual Physics
Notes on Chapter 8
Work & Energy

2. Work & Energy W = Fd Work is defined as Force x distance
Work is done in lifting a book one meter. Twice as much work is done in lifting the same book two meters.

3. Work & Energy
NOTE:
No work is done in sliding a book across a table. The book has gained NO ENERGY.

4. Work & Energy Power P = W / t
How fast I do work is known as
Power
Power is defined as
work done / time interval
P = W / t

5. Work & Energy UNITS: Force (F) = Newton Distance (d) = Meters
Work = N*m or Joule (J)
Time (t) = Seconds (s)
Power (P) = J/s or Watt (W)
(NOTE: One horsepower (hp) is equal to .75 kW or 7500 W)

6. This is known as Mechanical Energy
Work & Energy
Work = Δ Energy
Fd = Δ E (Energy)
This is known as Mechanical Energy

7. Work & Energy
Mechanical Energy is energy of position or energy of movement.
Energy of position is Potential (PE) = weight * height
PE = mgh
Energy of movement is Kinetic (KE) = ½ mass * speed2
KE = ½ m*v2

8. Conservation of Energy
Work & Energy
Conservation of Energy
“Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes”

9. Work & Energy Energy of position changes to energy of movement
or energy of movement to
energy of position.

10. Work output / Work input
Work & Energy
MACHINES:
A machine is a device used to multiply forces or to change the direction of forces.
Examples are : pulley’s and lever’s
How efficient a machine works is defined as:
Work output / Work input
Actual Advantage / Theoretical Advantage

11. Work & Energy
PROBLEMS
What is the work done in lifting a 100 kg block a height of 7 m?
A 40 kg boy runs up stairs to a floor 5 m high in 7 seconds. What is his power output?