Lesson 14 Objectives Calculate the ideal mechanical advantage

Lesson 14 •

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

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 force = Effort distance 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

• 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?

• Materials • Procedures 1. • 2. • 3,