1. Energy, Work & Power
WORK

2. Work
Defined as the amount of energy transferred to an object by a force over a distance.
Calculated by:
Joule (J): SI unit of work and energy.
1 Nm = 1 J
Where:
W=work (J)
F = Force magnitude (N)
∆d= distance (m)

3. Work has signs!
When work (or energy) is being put into a system, we say that it is positive work.
When work (or energy) is being extracted from a system, we say that it is negative work.

4. Example #1
A toboggan carrying two children (mass = 60kg) is sliding on a snowy surface with a coefficient of friction of 0.11 and comes to a stop in 25m.
Calculate the work done by the kinetic friction on the toboggan.
What sign would this work have?

5. Work & Gravity
To lift an object, an individual applies a force equal in magnitude but opposite in direction to that object’s weight.
Recall:
Eg.2: How much work is done to lift a 30kg object 3m into the air?

6. Work & Springs
Springs exert a force which depends on the displacement of its end.
How much it is either stretched, compressed or twisted.
Since the force changes, we need a new approach since our equation works for constant force ONLY ( )

7. Example #3 Data for a spring is given to the right.
Create a force vs. displacement graph
Determine the work done to stretch the spring 0.2m.
Determine the slope of the line of best fit.
Displacement (m)
Force (N)
0.1 5
0.2 10
0.3 15
0.4 20