Levers and Torque: More Practice

Levers and Torque: More Practice

Levers and Torque: More Practice

Classes of Levers: Student Learning GoalThe student will investigate the relationships

between force, distance, and torque for the load arm and effort arm of the three classes of levers (C2.4, C2.5).

Classes of Levers

SPH4C

1st Class Levers

A 1st class lever has the fulcrum in the centre:

The fulcrum may be positioned closer to the load or closer to the effort force.

1st Class Levers

A 1st class lever has the fulcrum in the centre:

Example: a seesaw

2nd Class Levers

A 2nd class lever has the load in the centre:

2nd Class Levers

A 2nd class lever has the load in the centre:

Example: a wheelbarrow

3rd Class Levers

A 3rd class lever has the effort force in the centre:

3rd Class Levers

A 3rd class lever has the effort force in the centre:

Example: the human forearm

Mechanical Advantage RevisitedThe ideal mechanical advantage of a lever is

defined as the ratio of the effort arm to the load arm:

L

E

d

dIMA

Mechanical Advantage RevisitedThe ideal mechanical advantage of a lever is

defined as the ratio of the effort arm to the load arm:

Note that for 3rd class levers, the IMA will be less than 1!

L

E

d

dIMA

Mechanical Advantage RevisitedThe actual mechanical advantage of a lever is

defined as the ratio of the load force to the effort force:

(and again, this may be less than 1)

E

L

F

FAMA

Mechanical Advantage Revisited

This mechanical advantage may be affected not only by friction but also by factors such as the weight of the lever itself.

E

L

F

FAMA

Efficiency

Efficiency is, as before:

Note that a lever can have a low (even less than 1) AMA and IMA but still have a high efficiency if the AMA is close to the IMA.

%100% IMA

AMAefficiency

More Practice

Three Classes of Levers Lab Activity