1. Work & Machines

2. Review Work When work is done, a transfer of energy always occurs.
Work is force exerted on an object that causes the object to move some distance
Force without moving a distance yields NO WORK!!
When work is done, a transfer of energy always occurs.

3. 1) Power and work Power is related to work.
The amount of work done in a certain amount of time.
Power = work/time
P = W / t
Units for power is - Watt(W)
It is a Joule/second (J/s)

4. 2) Power and Energy Power is also related to energy.
When energy is transferred from one object to another.
Power = energy/time
P = E/t

5. Machine A device that makes work easier or more effective
by changing the amount of force, the distance covered or the direction of the force

6. Mechanical Advantage (MA) -number of times a machine multiplies the effort force.
Ideal Mechanical Advantage (IMA)- theoretical performance of a machine if no energy was lost to friction.
IMA = resistance force / effort force
IMA = FR/FE
It’s a ratio- the units cancel.

7. Efficiency of a Machine
Since work is lost to friction, the amount of work obtained from a machine is always less than the amount of work put into it .
Efficiency = work output/ work input x 100
Remember that
work = force x distance

9. Inclined Plane
A sloping surface that can reduce the amount of force to do work.
IMA = length of incline / height of incline

10. Wedge
A one or two sided inclined plane that changes the direction of the force

11. Screw
an inclined plane wrapped around a cylinder

12. Lever A rigid bar that pivots over a fulcrum (a fixed point).
IMA = length of effort arm
length of resistance arm
Draw 3 classes of levers and give examples of each.

13. 1st Class Levers Notice how
The input & output forces are in opposite directions
The fulcrum is between the input & output forces
Examples include nail remover, paint can opener scissors, seesaw

14. 2nd Class Levers Notice how:
The input & output forces are in the same direction
Input force is farther away from the fulcrum than the output force
Examples include: wheel barrow, door, nutcracker

15. 3rd Class Lever Notice how:
The input & output forces are in the same direction
The input force is closer to the fulcrum than the output force
Examples include rake, shovel, baseball bat and fishing pole

16. What Class of Lever? 3 2 1 4 5 6 7
_______ 2. _______ 3. _______ 4. _______
5. _______ 6. _______ 7. _______ 8. _______
3rd Class 2. 1st Class 3. 1st Class 4. 2nd Class
5. 2nd Class 6. 3rd Class 7. 1st Class 8. 2nd Class 8

17. Wheel and Axle
two circular objects attached together about a common axis
Wheel is the large cylinder
Axle is the small cylinder
IMA = Radius of the wheel
Radius of the axle

18. Pulley A cord wrapped around a wheel.
IMA = the number of ropes that support the weight