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WORK 8.1
Chapter Eight: Work
8.1 Work
8.2 Efficiency and Power
Chapter 8.1 Learning Goals
Tell what it means to “do work” in a
scientific sense.
Apply an equation to determine the
amount of work done by a force.
Infer that work requires energy.
Investigation 8A
Manipulating Forces
Key Question:
How do simple machines work?
8.1 Work
 In science, work is a
form of energy you
either use or get when
a force is applied over
a distance.
 You do 1 joule of work
if you push with a
force of 1 newton for
a distance of 1 meter.
8.1 Work
 When thinking about work, remember that
work is done by forces that cause
 If nothing moves (distance is zero), then
no work is done.
8.1 Work
Force (N)
Work (joules)
Distance (m)
8.1 Work and energy
Doing work always means transferring
The energy may be transferred to the object
you apply the force to, or it may go
somewhere else.
8.1 Work and energy
You can do work to
increase an object’s
potential energy.
Then the potential
energy can be
converted to kinetic
8.1 Work
 A raised object’s potential
energy equals the amount of
work it can do as it moves
 The amount of kinetic energy
an object has equals the
amount of work the object
can do by exerting force as it
8.1 Work
 If force is equivalent to the
weight of the object in
newtons, and
 height (h) is equivalent to
distance (d),
 Then multiplying the weight
by height gives you the
amount of work the object
can accomplish as it moves
down (as well as its potential
8.1 Work
 Force A does no work
because it does not
cause the block to move.
 Force B is applied at an
angle to the direction of
motion, so only part of
force B does work.
 The most effective force
to move the block is
force C.
Solving Problems
 How much work is done by a person
who pulls a cart with a force of 50
newtons if the cart moves 20 meters
in the direction of the force?
Solving Problems
1. Looking for:
 …work done by person
2. Given:
 …force = 50 N (forward);
 …distance = 20 m
3. Relationships:
 Work = force x distance
4. Solution
 50 N × 20 m = 1,000 joules.