1. Chapter 8 Rotational Equilibrium and Dynamics
pgs

2. Objectives Explain how machines make work easier.
Calculate mechanical advantage of machines.

3. Simple Machines
A machine is any device that transmits or modifies force
Six types of simple machines:
Lever Pulley
Wheel and Axle Wedge
Inclined Plane Screw

4. Simple Machines

5. Mechanical advantage (MA)
The ratio of the output force relative to the input force of a machine
Machines can alter the force and the distance moved

6. Mechanical Advantage (MA)
Output Force Fout = = Input Force Fin MA

7. Efficiency (eff) A measure of how well a machine works
Work Output Wout
= =
Work Input Win
eff

8. Efficiency (eff)
Efficiency of an ideal machine (no energy lost to friction) is 1 or 100% efficient
Efficiency of real machines is always less than 1

9. A person lifts a 850 N box by pushing it up an incline
A person lifts a 850 N box by pushing it up an incline. If the person exerts a force of 325 N along the incline, what is the mechanical advantage of the incline?

10. The efficiency of a squeaky pulley system is 0. 85, or 85%
The efficiency of a squeaky pulley system is 0.85, or 85%. What force is exerted on the machine if a rope is pulled 18.0 m in order to raise a 60. kg mass a height of 3.5 m?