Mechanical Advantage

What does it mean to be in rotational equilibrium?

•All torques are balanced•The lever is not rotating

If in rotational equilibrium:

EEE dFT LLL dFT

L

E

E

L

EELL

EL

d

d

F

F

dFdF

TT

Mechanical Advantage

•A measure of how much easier the machine makes a task

•Ratio of output force to input force•Known as force amplification

Ideal Mechanical Advantage (IMA)•The mechanical advantage the machine

will provide if all conditions are perfect •No friction, no wear, all forces applied in

the proper directions

L

E

d

dIMA

Actual Mechanical Advantage (AMA)

•The mechanical advantage the machine provides when used

•Forces are measured

E

L

F

FAMA

•If the force is transmitted perfectly (100% efficient)

If the force is not transmitted perfectly

IMAAMA

d

d

F

F

L

E

E

L

IMAAMA

d

d

F

F

L

E

E

L

•Copy Table 1 from Pg 88 in text

IMA - Pulley

•IMA of a pulley is based on the number of strands supporting the mass

% Efficiency

%100% xIMA

AMAEfficiency

How effective a machine is at transforming an input into an output

Example 1:

The following pulley system carries a mass of 30.0kg.

Calculate:1) Actual Mechanical

Advantage2) Ideal Mechanical

Advantage3) % Efficiency

FE= 100N

Example 2:A pulley system has a 20.0kg load attached

to it. The load arm is 50.0cm, the effort arm is 200cm and the effort force is 60N.

Calculate:a) FL

b) AMAc) IMAd) % Efficiency