# Physics 3 Revision

HideShow resource information
• Created by: ThÃ©a
• Created on: 15-05-13 11:41

## Levers

-See-saw

-Door

-Wheelbarrow

-Crowbar

-Tyre pump

-Wheel/tyre spanner

Doing all of these things is called a 'turning force'.

What defines this is the amount of force applied and how far it is from the point.

1 of 6

## Moments

Moment:

-Turning effect of a force

-  Moment (Nm) = force (N) x perpendicular distance from pivot to line of action

Principle of moments:

For objects in equilibrium:

The sum of all the clockwise moments = Tthe sum of all the anticlockwise moments

2 of 6

## Hydraulics

A vacuum is a space where there are no particles at all.

Liquids cannot be decompressed, because the particles are already very close together.

Therefore, liquids can be used to send forces froom one place to another in hydraulic systems.

1 Pa = 1 N/cm²

Pressure = force / area

The pressure stays the same throughout the liquid.

3 of 6

## Hydraulic Systems

Pressure throughout the liquid must be the same, so pressure in the bigger cylinder must be equal to the pressure in the smaller cylinder.

The smaller cylinder acts as a force magnifier.

F / A = f / a             and so          F = f A / a

Output force = force on small piston x (area of large cylinder / area of small cylinder)

Uses of Hydraulics:

- Hydraulic brakes in cars and some mountain bikes

- Hydraulic press and jack

4 of 6

## Circular Motion

Examples:

-Planets orbiting the sun - Gravitational attraction and pull of the sun

-Electrons orbiting the nucleus of an atom - Maintained by electrostatic attraction between positive protons and negative electrons

-A conker being spun on a string - Tension in the string (Centripetal Force)

5 of 6

## Centripetal Force

Think of the conker on a string. If the tension is removed, then the circular path will not be maintained.

This force acts towards the centre of the circle and is referred to as the CENTRIPETAL force.

This is an unbalanced force and is responsible for the conker changing direction constantly.

It thus causes the velocity to change.

The centripetal force therefore causes an acceleration that acts towards the centre of the circular path.

The force and acceleration MUST be at right angles, TOWARDS the centre.

Increasing the object's mass, increasing the object's speed, and decreasing the radius of the circle, all increase the centripetal force.

6 of 6