1. Applied Physics and Chemistry Work Lecture 4
Efficiency and MA
Applied Physics and Chemistry Work Lecture 4

2. Mechanical Advantage
Mechanical advantage tells how much the machine is helping us
Two ways to calculate MA:
IMA: Ideal Mechanical Advantage
Neglects the effect of friction
IMA = de/dr
AMA: Actual Mechanical Advantage
Includes the effect of friction
MA = Fr/Fe

3. MA Problems
You got roped into helping your parents’ friends move. They have a ramp leading up into the back of a truck. The ramp is 6 m long, and the back of the truck is 1.5 m off the ground. What is the MA of this simple machine?
When watching a circus act, you notice the tumblers using a first class lever and wonder how if one of them jumps, it can propel two of them into the air.  When the tumbling lever is measured, it shows the effort arm (which they jump on) is 8 meters long, the resistance arm (where their tumbler is being propelled from) is 2 meters long.  What is the mechanical advantage of this lever?

4. More MA Problems
A toy car has the following measurements for its wheels:  the radius axle (the small wheel) measures 1 cm.  The radius of the larger wheel (the one that touches the pavement) measures a whopping 10cm.  What is the mechanical advantage of these large wheels? 
A 10 m ramp is used to lift a 600 N box to a height of 2 m. The effort force as a person pushes the box up the ramp is 160 N. What is the AMA of this simple machine?
What is the IMA of the ramp?

5. Efficiency
In a real machine, not all input work is available as output work Efficiency is the ratio of output work to input work
Eff = (Wo/Wi) x 100
Eff = (MA/IMA) x 100

6. Efficiency Problems
A 10 m ramp is used to lift a 600 N box to a height of 2 m. The effort force as a person pushes the box up the ramp is 160 N. What is the efficiency of this simple machine?
A worker uses a pulley system to raise a 24 kg carton m. A force of 129 N is exerted and the rope is pulled 33 m. What is the efficiency of the system?