1. Topic 2.2 – The Science of Work
Mechanical Systems

2. Work
Work is done when a force acts on an object to make the object move.
According to Science, doing your homework is not actually doing work! 
MOVEMENT HAS TO BE DONE BEFORE WE CAN SEE ANY WORK BEING DONE!

3. Calculating Work The formula for Work is: Work = Force x Distance
W = F x d
F is the force being exerted on an object
d is the distance the object moves
W is measured in JOULES (J)

4. Lift a Chair
If you lifted your chair onto your desk, how much work would you do? Assume that you have to exert a force of 50 N to lift the chair and your desk is 0.4 m high.
W = F x d
= 50 N x m = 20J

5. Energy and Work
Energy and work are closely related because without energy, there would be no work.
Example:
When you ride a bike, you exert a force on the pedals.
The chain transfers the force to the wheels causing you to move.
YOUR ENERGY IS USED TO MOVE THE BIKE

6. Example What would the work be to lift the box up 2 m? W = F x d
80N 2m
What would the work be to lift the box up 2 m?
W = F x d
= 80N x 2m
= 160 J

7. Work and Machines
Using a machine does not mean that less work is done.
You use the machine so you don’t have to exert as much force.
BUT YOU STILL DO THE SAME AMOUNT OF WORK!

8. Practice Problems
1. You use a force of 40 N to push a box of books 3.2 m along the floor. How much work have you done?
2. Calculate the work done in the following situation:
A 500 N box is lifted 0.5 m.

9. Topic 2.3 – The big movers
Mechanical Systems

10. Hydraulic Systems
A hydraulic system uses a liquid under pressure to move loads.
A hydraulic system increases the mechanical advantage

11. Pascal’s Law
Pascal says that pressure applied to an enclosed fluid is transmitted equally in all directions throughout the fluid.

12. Pressure in fluids
Hydraulic systems work because they use fluids that are under pressure.
Pressure is a measure of the amount of force applied to a given area.
Pressure = Force Area
p = F A
Units for pressure are Pa (Pascals)

13. Mechanical Advantage Remember: MA = OF IF = 500 N 20N = 25
THIS IS A HUGE MECHANICAL ADVANTAGE!
Fin= 20N
FOUT= 500N

14. Why such a huge mechanical advantage?
The mechanical advantage is so huge because a hydraulic system allows you to use a smaller force on the small piston to produce a larger force on the large piston

15. Example
Assume a small piston has an area of 4 cm2 and the force it applies to a fluid is 20 N. What is the pressure?
p= F A
p = 20 N 4 cm2
= 5 Pa

16. Example continued
Assume a large piston has an area of 100 cm2 and a force of 500 N will raise a load. What is the pressure?
p= F A
p = 500 N cm2
= 5 Pa

17. Soooo… the pressure of the large piston is the SAME AS the small piston!
PASCAL was correct – fluid does exert the same pressure in all directions!
Fsmall = Flarge _____ ____ Asmall = Alarge

18. Example Find the area of the large piston. Flarge= 500N Fsmall= 20N
AREAsmall=4cm2
AREAlarge= X
Find the area of the large piston.

19. Questions to try: 1. What does a pascal measure?
2. A hydraulic lift has 2000 N applied to an input piston that has an area of 50 cm2. The output piston has an area of 200 cm2.
What is the pressure on the liquid exerted by the input piston?