simple machines. recap a force is any action that changes or tends to change the size, shape and/or...

SIMPLE SIMPLE MACHINESMACHINES

RECAP• A force is any action that changes or tends to

change the size, shape and/or state of rest/motion of a body.

• A force is NOT a matter. It has NO mass and does not take up space.

• We define force as a push or a pull.

• SI unit for force is Newton (N).

• We can see effects of forces everyday in our daily lives eg, compressed, stretched, bent or twisted.

LEVERLEVERA simple machine that turns about a fixed

point (F) when a force (E) is applied to move another force (L).

Levers help us to do work byLevers help us to do work by

• Reducing the effort needed to overcome a load

• Producing a large movement from a small movement.

LOAD

FULCRUM

EFFORT

fixed point

applied force

How does lever make work easier?

• Using small effort to overcome a bigger load.

– An example is the see-saw

To overcome a load with less effort.

•Effort should be as far away as possible from the fulcrum.

loadEffort

fulcrum

•Load should be as near as possible to the fulcrum.

To overcome a load with less effort.

load

Effort

fulcrum

Small effort, Big load

• Distance moved by the effort is MORE than the distance moved by the load.

effort

fulcrum

load

distance

Big effort, Small load

• a small movement of the effort causes a large movement of the load.

• Greater amount of effort needed to move the load.

fulcrum

effortload

Question!

Position A

• Which position require a bigger effort?• What does represent?• What if is moved nearer to the load?

effort effort

Position B

INCLINED PLANESINCLINED PLANES

A slanted surface that joins two different levels.

• Reducing the effort needed to move a heavy load.

•BUT!

• Effort will have to move through a longer distance.

Inclined planes help us to do work by

load

Distance moved by effort when box is lifted vertically.

load

Distance moved by effort along the plank

Examples of inclined planes

ladder

ramp stairs

slide

Questions!

A B

C D

• What kind of simple machine is a ramp?It is a lever

• What is the advantage of using ramp B? It will need the least effort to move the load.

• What is the advantage of using ramp D?The load will travel the shortest distance.

• What is the difference between A and C?A is inclined at a smaller angle than C.

• How can we convert a plank into a ramp?By supporting a plank at an angle.

B

D

AC

PULLEYSA wheel with a groove where a rope can go

over. It is used for lifting objects.

What is a pulley?

A pulley is a wheel with a groove where a rope or string can go over.

• Fixed pulley

• Movable pulley

• Pulley system

FIXED PULLEY

• A pulley in a fixed position.

• Eg : flag pole.

• It does not reduce the effort used to lift a load.

• It makes work easier by changing the direction of the applied force (effort).

MOVABLE PULLEY

• Not a fixed pulley

• Can be used to lift an object with a smaller effort.

• BUT!

• Effort has to move through a longer distance than the load.

• DOES NOT change direction of the applied force.

PULLEY SYSTEM

• Combines the fixed pulley and the movable pulley.

• Direction of the force is changed

• A smaller effort is needed to raise a heavy load.