1. Work Power and Machines
Concepts of Physics

2. Work can be best defined as
Doing manual labor
Applying a force over a distance with no motion
Applying a force over a distance with motion
Exerting energy while applying a force

3. The units for work are Watts Calories Amps Joules Volts
Calories per pound

4. Joules could be used to measure
The work done lifting a bowling ball
The potential energy of a bowling ball held in the air
The kinetic energy of a rolling ball
All of the above
None of the above
Both B and C

5. 1 Joule is equal to
1 N∙m
1 N∙s
1 kg∙m2/s2
Both A and C
Both B and C

6. A force of 20 N is applied to picking a 15 kg ball 2 m high
A force of 20 N is applied to picking a 15 kg ball 2 m high. What is the work done?
600 Joules
40 Joules
40 Watts
600 Watts
600 Amps
40 Amps

7. The units for power are Watts Calories Amps Joules Volts
Calories per pound

8. In science work has a specific meaning
Definition for work:
A quantity that measures the effects of force acting over a distance.
In science work has a specific meaning
Work is done only when force causes a change in MOTION

9. Work Equation Work = Force x Distance Example:
A man lifts a ball 2 meters in the air while exerting a force of 190 N. What is the work done?
Example 2:
A man holds a massive barbell stationary 2.5 meters in the air while applying a huge force.

10. Measurements of Work
Since work = Force x Distance than the SI units for work must be N∙m.
This is also known as a Joule (J).
1 kg ∙ m2/s2 = 1N ∙ m = 1 J

11. Power
Does running up the stairs require more work than walking up the stairs?
NO! remember Work = Force x Distance,
time is not involved.
When we involve time we are talking about POWER

12. Power Power = Work/time
Power is defined as the rate at which work is done, or how much work is done in a certain amount of time.
Equation form:
Power = Work/time

13. Power is measured in WATTS (W)
1 Watt is the amount of
Power required to 1 J of in
1 sec.

14. Example 1
It takes 100 kiloJoules (kJ) of work to lift an elevator 18 m. If it takes 20 sec for this to happen what is the average power during the process?
18 m