14.3: Mechanical Advantage and Efficiency

1. 14.3: Mechanical Advantage and Efficiency

2. What are some things humans can’t do without some kind of tool? Machines give us some sort of advantage to accomplish tasks!

3. Mechanical Advantage Machines can take a small input force and create a large output force. The mechanical advantage of a machine is the number of times that the machine increases an input force. There are two ways to calculate the mechanical advantage of a machine: actual and ideal. http://www.ceramic-photos.co.uk/images/safety_signs/Warning_forkLift_Truck.gif

4. Actual Mechanical Advantage The actual mechanical advantage (AMA) equals the ratio of the output force to the input force. AMA = Output Force / Input Force

5. Ideal Mechanical Advantage The ideal mechanical advantage (IMA) is the maximum mechanical advantage a machine can have. To have the maximum mechanical advantage, there must be no friction.

6. Ideal Mechanical Advantage If there is no friction, then none of the input force will be lost. So the input force is the same as the output force. In this case, the only thing that matters is the locations of the forces and the distances over which they act.

7. Ideal Mechanical Advantage IMA = Input distance / Output distance http://www.iq.poquoson.org/8science/workmachines/wkmach3.gif

8. AMA vs IMA AMA is what actually happens IMA is what could happen without friction Since there is always some friction, AMA is less than IMA.

9. Efficiency We always want to see how efficient a machine is. Most cars get at least 20 miles per gallon. This is an example of efficiency. We say that a car that gets 30 miles per gallon is more efficient. With efficiency, we compare how much work we get from the work we put into a machine.

10. Efficiency Efficiency = (Work output / Work input) X 100% Because there is always some friction, the efficiency of any machine is always less than 100 percent.