Work
What is it?
How is it calculated?
How is it measured?
New Terms
 Work – a force applied over a distance.
 Joules (J) – SI unit for work. 1 J = 1 N*m so, a Joule is
equal to a force of 1 N acting over a distance of 1 m.
 Foot Pound-Force – English unit for work. Used in
engineering fields commonly. 1 ft-lb is equal to 1.36 J.
Work Examples
 To have work in science, BOTH a force AND a distance
NEED to be involved!
 Holding 300 pounds still over your head is hard, but is NOT
an example of work.
 Lifting the weight is, pushing a chair is, work is done to move
an elevator from the first floor to the 5th floor.
Work Examples, cont.
 Which example shows work being done?
 Depends. They both have a force. Which one has movement
(the animation isn’t working on the website)?
Calculating Work
 Formula
Work = Force x Distance
 Units: Work is in Joules, Force is in Newtons and Distance is
in Meters
 Example: How much work is done moving a couch with a
force of 500N a distance of 10m?
Answer to Previous Question
 W=?J
 F = 500 N
 D = 10 M
 So, W = Fd
 W = 500 x 10
 W = 5000 J (Joules can be written as N*m, so the answer
could be 5000 N*m)
More Calculations
 Work = F x d, F = m x a, a = v/t, v = d/t
 You can calculate work if given a distance, a time, and a mass.
 How much work is done moving a 5kg object 2m in 10s?
Problem Solution
 Step 1: Calculate v. V= 2/10. V=0.20 m/s
 Step 2: Calculate a. A=(0.2-0)/10. A= 0.02m/s2
 Step 3: Calculate F. F=5x0.02. F=0.10N
 Step 4: Calculate W. W=0.10x2. W=0.20J
Assessment
1.
What is the SI unit of measurement for work?
2.
How far would a person need to move an object to exert
500J if the object required 125N to move?
3.
How much force does it take to move a bed 10m if
150,000J are used moving the object?
Answers
1.
Joule (J)
2.
4m
3.
15,000N