Levers

For Mrs. Berg’s Science Class

A lever consists of a rod or bar that rests and turns on a support called a fulcrum.

effortresistance

A force of effort is applied at one end of the rod to lift a load placed at the other end. A lever can help lift a weight with less effort.

effort

resistance

fulcrum

Prying something loose with a crowbar is using a lever. Some machines, such as a catapult,

use a lever to hurl objects.

Here is a catapult you could make.

Three Classes of Levers

• First Class Lever– The fulcrum is between the effort force and

the resistance force.

resistance

fulcrum

effort

Three Classes of Levers

• Second Class Lever– The resistance is between the effort and the

fulcrum.

Three Classes of Levers

• Third Class of Lever– The effort is between the fulcrum and the

resistance.

First Class Lever

Second Class Lever

Third Class Lever

Levers on the internet

• Check out these websites!

• http://www.dynamicscience.com.au/tester/solutions/hydraulicus/simplemachineslevers1.htm

• LEVERS in our BODIES!• http://www.dynamicscience.com.au/tester/solutions/

hydraulicus/humanbody.htm

• http://www.montgomery.k12.ky.us/camargo/Projects/simplemachines/simplemachines.htm

Levers in the Body• An example of a first-class lever is the joint between the

skull and the atlas vertebrae of the spine: the spine is the fulcrum across which muscles lift the head.

An example in the human body of a second-class lever is the Achilles tendon, pushing or pulling across the heel of the foot.

An example of a third-class lever in the human body is the elbow joint: when lifting a book, the elbow joint is the fulcrum across which the biceps muscle performs the work.

First Class Lever

Second Class Lever

Third Class Lever

Key Concepts:

• A lever pivots on one fixed point – up and down or side to side.

• To use a lever, effort is applied to one end by pushing or pulling. The lever transfers this force to move the load.

Key Concepts:

• A lever can make work easier in the following ways:– Increasing the force being applied.– Changing the direction of the force.– Increasing the distance or speed at which the

job is done.

Vocabulary• Simple Machine- a machine with one moving part• Lever –a beam, bar, rod that turns or rotates on or around a

fixed point• Fulcrum – a fixed point that allows the beam to rotate around it.• Work – the use of force to move an object• Force –any kind of push or pull on an object• Effort – the force that is used to do the work• Resistance – the force (load) that works against the effort• Load –the object or resistance being moved by the effort• Friction – the force that is caused when 2 surfaces rub together

as an object moves• Mechanical Advantage – how the simple machine increases the

effort

beam

bar

rod

board

rotate

Turn

effortResistance / Load

fulcrum

work

friction

Mechanical Advantage