2.
Work
Work is the transfer of energy that
occurs when a force makes an object
move.
2 conditions for work to be done
An applied force must make the object move
Movement must be in the same direction as the
force.
Force
Movement
3.
Work
How is the scientific definition of work
different from the every day meaning?
Force
Movement
4.
Work
When work is done transfer of energy
always occurs.
When you work on an object, you
increase its energy.
5.
Calculating Work
Work = applied force * distance
Or w=Fd
Create a calculation triangle to make it
easier to solve for “w”.
W
F x d
6.
Calculating Work cont.
A force of 75N is exerted on a 45 kg
couch and the couch is moved 5m. How
much work is done in moving the couch?
The brakes on a car do 240,000 J of
work in stopping the car. If the car
travels a distance of 50m while the
brakes are being applied, what is the
total force of the brakes on the car?
7.
Power
Power is the amount of work done in one
second.
Rate at which work is done
8.
Calculating Power
Power = work/ time
Create a calculation triangle to make it
easier to solve for “p”.
W
P x t
9.
Calculating Power cont.
To lift a baby from a crib 50 J or work are
done. How much power is needed to lift
the baby in 0.5s?
The power produced by an electric
motor is 500 W. How long will it take the
motor to do 10,000 J of work?
10.
Machines
A machine is a device that makes doing
work easier.
It increases the force that you apply.
11.
Machines cont.
Input Force: force that is applied to the
machine. = Fin
Output Force: the force applied by the
machine. = Fout
Mechanical advantage is the ratio of the
output force to the input force
MA = Fout/Fin
Efficiency % = Output work/ input work x 100
12.
Machines cont.
Friction causes energy of the output
force to be lost as heat.
This means Wout is smaller than Win
How would lubricating a machine affect
the output force exerted by the
machine?
Ideal MA is one without friction
13.
MA and Efficiency Triangles
Create a triangle for
Mechanical
Advantage
Create a triangle for
efficiency.
Fout
MA x Fin
Fout
Eff. x Fin
x 100%
14.
Calculating MA and Efficiency
The mechanical advantage of a hammer
if the input force is 125 N and the output
force is 2,000 N.
Find the efficiency of a machine that
does 800 J of work if the input work is
2,400 J.
15.
Simple Machines
6 basic types
Levers
Pulleys
Wheel and Axel
Inclined Planes
Screw
Wedge
View Simple Machines
16.
Levers
There are 3 types of Lever:
First-Class: Fulcrum is between input &
output force.
Second-Class: Output force is between the
fulcrum & the input force
Third-Class the input force is between the
fulcrum and the output force.
View Examples
17.
Pulleys
Fixed: Changes only the direction of YOUR
force. (4N in gets 4N out)
Movable: the attached side of the rope
supports half of the weight. Ex. For a 4N object
attached side supports 2N while you only do
2N of work.
Block and Tackle: Made up of 2 fixed & 2
movable pulleys & weight is divided evenly
among all of them.
View Pulleys
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