Biomechanics Principles of Levers

Principles of Levers

Aim:

To understand how the three types of

levers work and appreciate the

advantages/disadvantages of each

one.

Principles of Levers

Expected Knowledge

• Force

• Velocity

Principles of Levers

Key Vocabulary

• Lever

• Fulcrum

• Resistance

• Effort

Levers are…

• Simple machines that help us apply

force.

• Rigid structures, hinged at some part with

forces applied at two other points.

We have levers within our body, and also

use them externally for many different

reasons.

All levers have three parts:

• Fulcrum

• Resistance

• Effort

Fulcrum

The pivot point.

Resistance (or load)

The weight that needs to be moved.

Effort

The force that is applied to move the

resistance (or load).

Functions of a Lever

Levers perform two main functions:

To increase the resistance

(or force) that can be moved with

a given effort e.g. a crowbar.

To increase the velocity at

which an object will move with a

given force. E.g. A golf club.

Classes of Levers

There are 3 classes of levers.

Each is structured in a different manner

and has different advantages.

First Class Levers

The fulcrum lies between the effort and the

resistance.

First Class Levers

Using a crowbar to move a rock.

First Class Levers

Using a hammer to pull out a nail.

First Class Levers

A see-saw.

First Class Levers

Up and down movement of the

head about the atlas joint.

First Class Levers

Pulling an oar in a row boat.

Second Class Levers

The resistance lies between the fulcrum and

the point of effort.

Second Class Levers

The movement of the foot when walking.

(the calf muscle provides the effort and the ball of the foot is the pivot)

Second Class Levers

Opening a door by

the handle.

Second Class Levers

Opening a bottle with a bottle opener.

Second Class Levers

Pushing a wheel barrow.

Third Class Levers

The effort lies between the resistance and

the fulcrum.

Third Class Levers

Biceps curl.

Third Class Levers

Fishing with a rod.

Third Class Levers

Swinging a bat to hit a ball.

Application

Long levers

provide amplified power at the

expense of speed of movement of the object

being moved.

Examples:

– Using a jack to lift a crashed car.

– Using a knife to get the lid off a tin.

Application

Short levers

provide speed

at the expense of power

Example:

Levers designed to accelerate objects include:

- Most body limbs used for throwing or kicking

because the muscle inserts near the pivot

point.

Application

• Can you think of sporting examples where

there are longer and shorter levers?

• What happens to the effectiveness of a

lever if the fulcrum is moved closer or

further away from the load?

Revision

Question One: Fill in the blanks

Levers are simple machines which helps us apply

____(a)____ . They have ___(b)___ parts. The ___(c)___

is the pivot point. The ___(d)___ (or load) is the weight that

needs to be moved. The ___(e)___ is the force that is

applied to move the resistance.

Revision

Question Two: Label the diagram

Revision

Question Three: First, Second or Third Class?

(a)

(b)

(c)

The fulcrum lies between the effort and

the resistance.

The resistance lies between the fulcrum

and the point of effort.

The effort lies between the resistance and

the fulcrum.

Revision

Question Three: First, Second or Third Class?

(d) (e)

(f)

Revision

Question Three: First, Second or Third Class?

(g) (h)

(i) (j)

Revision

Question Three: First, Second or Third Class?

(k) (l)

(m) (n)

Application

• How would you change your grip on a softball

bat if you wanted to hit the ball with more force?

Experiment with this with a partner.

• With a partner find another physical activity

example that will be able to demonstrate

application of the principles of levers, showing

what happens when you change the length of

your lever.