The Mechanical Advantage of Machines Lesson 14 \ The Mechanical Advantage of Machines

Objectives Calculate the ideal mechanical advantage of inclined planes and pulley systems. Calculate the actual mechanical advantage of inclined planes and pulley systems Compare actual and ideal mechanical advantage

Getting Started Which is the best machine: an inclined plane, a pulley or a lever? How would you decide which is the better machine? What things would you look at? Why would someone want to know the mechanical advantage of one machine over another?

Getting Started con’t What is the difference between ideal mechanical advantage and actual mechanical advantage?

Comparing mechanical advantages Ideal mechanical advantage tells how much the machine increases the effort distance when doing work. Actual mechanical advantage tells how much the machine reduces the effort force when doing work.

Ideal Mechanical Advantage effort distance load distance effort distance load distance

Actual Mechanical Advantage load force effort force

Vocabulary – Lesson 14 The factor by which a machine multiplies the effort force is mechanical advantage. The ratio of effort distance to load distance when a machine does work is ideal mechanical advantage. The ratio of load force to effort force needed to lift or move a load is actual mechanical advantage.

IMPORTANT!!!! Ideal mechanical advantage is the mechanical advantage assuming the machine operates at 100% efficiency. A machine will never operate at 100% efficiency because of friction, therefore actual mechanical advantage will ALWAYS be less than ideal.

What does it mean? So…what does it mean if a machine has an ideal mechanical advantage of 4? It means the effort distance needed to raise a load must be 4 times greater than the load distance.

What does it mean? What does it mean if a machine has an actual mechanical advantage of 3 N? It means that if a machine had a load force of 12.0 Newtons, your effort force would be reduced to only 4 N to pick the load up using the machine.

Explanation If there were no friction involved in doing work, then Load force = Effort distance Effort force Load distance

Explanation When there is no friction in a system, these two ratios are equal. When there is friction in a system, as there always is, these two ratio’s will be unequal.

Explanation When friction is present, the effort force increases because it must both lift the load and overcome friction. The load force, load distance and effort distance stay the same. The increase in effort force results in a decrease in the machine’s actual mechanical advantage which causes it to be less than the ideal mechanical advantage.

Lesson 14 Questions

Which slope has the largest actual mechanical advantage? Which slope has the largest ideal mechanical advantage? Which pulley had the greatest ideal mechanical advantage? Which pulley had the smallest actual mechanical advantage? Why would you want to use a pulley that had a small mechanical advantage?

Hypothesis If ________________________ then______________________ Because _________________________

Procedures Materials Procedures 1. 2. 3,