1. Work and Power

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