Work
Physics
Ms. Li
Does he do work?
 waiter
who carried a tray full of meals above his
head by one arm straight across the room at
constant speed
Questions
 Strawberry
uses a force of 0.75 Newtons to
drags his pet mouse 3 meters to give to me as a
gift. How much work did Straw do?
 Kiwi,
mass 8 kg leaps from the ground to his
cat tree a distance of 1.5 meters. How much
work did he do?
What is work
 Work
is done when a force causes an object to
move in the direction that the force is applied.
 Work is a scalar quantity
 The unit for work is the Joule (J)
How is work done?
A
force must cause the object to move.
 No move, no work
 Only the force that acts in the direction of the
movement applies.
 You need energy to do work.
How do you calculate work
 Work
= force times Displacement
 Displacement
is the magnitude and direction from
where an objects starts from, and where it ends up.
(straight line)
Example

A wagon is pulled with a
force of 100 N along the
handle that is at an angle
of 30 degrees. If the
wagon moves 35 m
horizontally, what is the
work done on the wagon?
100 N
On board
Graphing
The area under a force vs.
displacement graph is the
work done by the force.
 Example: a block is pulled
at a constant speed along a
table with a force of 10. N
over a distance of 1.0 m.
 See graph (The area of the
shaded part is the amount
of work done on the block.

Force (N)
Displacement (m)
Power
 Work
can be done at different speeds
 The faster the work is done the more Power output.
Formula:
P = W/t
P = (F*d)/t
P = F*v
Example
How much work is done
on a 40 kg boulder when
you lift it 3m?
 What power is expended if
you lift the boulder a
distance of 3m in a time of
1.5s?
 What was the average
speed the boulder was
lifted?

Vocab
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energy - ability to produce change in its itself or the environment - ability to
produce work
kinetic energy - energy resulting from an object in motion
work - product of the force exerted on an object and the distance the object moves
in the direction of the force
work-energy theorem - Work is the transfer of energy by means of forces. The
work done on the system is equal to the change in energy of the system
joule - SI unit of work. It equals a Newton-meter.
power - rate of doing work. That is power is the rate at which energy is
transferred. Work done per second
watt - SI unit of work. It equals a Joule per second. A kilowatt = 1000 watts.
Units
Variable
Symbol
Units
Symbol
kinetic energy
KE
Joules
J
Potential energy PE
Joules
J
Work
W
Joules or Newton-meters
J or N-m
Power
P
Watts
W
Ready, Launch and Peak Positions