2. Simple Machines
Device that makes doing work easier is a machine
Machines increase applied force and/or change direction of applied force to make work easier

3. Effort and Resistance
Force applied to machine is effort force
Resistance force – force applied by machine to overcome resistance

4. Energy and Simple Machines
Amount of energy the machine transfers to the object cannot be greater than the amount of energy transferred to the machine

5. Energy and Simple Machines
An ideal machine with no friction would have the same input work and output work
Some energy transferred is changed to heat due to friction

6. The number of times a machine multiplies the effort force.
Mechanical Advantage
The number of times a machine multiplies the effort force.
MA = Resistance Force
Effort Force

7. Efficiency
Measure of how much of the work put into a machine is changed into useful output work by the machine.
Efficiency =
x 100
out W in

8. Lever Bar that is free to pivot about a fixed point called the fulcrum
MA of lever
depends on the
placement of
the fulcrum

9. Simple Machines
Which lever will allow the weight to be lifted with the least amount of force?
fulcrum
fulcrum
It is easier to lift a weight when the fulcrum is closer to the weight being lifted. 9

10. Simple Machines
Below is a picture of a perfectly balanced system. Describe how mass affects the distance from the fulcrum.
100 g
200 g
fulcrum
The greater mass is closer to the fulcrum.
Notice that is twice as big and half as close.
We always measure to the center of mass. 10

11. Pulley Grooved wheel with a rope or cable running along a groove
The greater the number of times the cable wraps around the pulleys, the greater the MA.

12. Simple Machines
Which pulley system will allow the weight to be lifted with the least amount of force?
Moveable pulleys, often grouped together in block and tackle systems, reduce the amount of force needed to lift an object.
Block and Tackle 12

13. Wheel and axle
Machine with two wheels of different sizes rotating together

14. Simple Machines
Gears are a type of simple machine. While it takes less force to spin the larger wheel, the smaller wheel spins at a faster rate. 14

15. Inclined Plane
Sloping surface that reduces the amount of force required to do work

16. Which ramp would it be easiest to slide a box up to the given height?
Simple Machines
Which ramp would it be easiest to slide a box up to the given height?
Making ramps longer lowers the amount of force needed to move an object up the ramp. 16

17. Wedge
Inclined plane with one or two sloping sides

18. Screw
Inclined plane wrapped in a spiral around a cylindrical post

19. Compound machine
Uses a combination of two or more simple machines

20. What force is it that opposes this motion?
Efficiency
The efficiency of machines can be determined by using a simple formula found on the formula chart.
Machines are always less than 100% efficient because of the force that opposes motion between the parts of the machine.
What force is it that opposes this motion?
Friction opposes the motion in the machines. Friction converts the machine’s work into heat. 20

21. Formulas W = F x d P = Work/t MA = Resistance Force Effort Force W out
Vf = Vi + at
d = Vi t + ½ at2
2ad = Vf2 – Vi2
d = ½ (Vf + Vi) t
MA = Resistance Force
Effort Force
W = F x d
P = Work/t
KE = ½mv2
Efficiency =
x 100
out W in
GPE = mgh
ME = KE + PE