# AQA GCSE PHYSICS UNIT 3 SECTION 1

Revision cards with notes covering section 1 and the start of section 2

HideShow resource information
• Created by: dnaiel
• Created on: 26-05-11 18:23

## Turning Effects

To unscrew a nut you normally use a spanner. You do this by putting the spanner on the nut and pushing against it. The turning effect of this is called the moment.

To Increase the moment you can:

• Increase the perpendicular distance from the pivot i.e. The length of the spanner
• Increase the applied force i.e. How hard you push the spanner

You can work out the moment using the below equation

Moment    =    Perpendicular Distance    x    Aplied Force

(Newton Metres, Nm)              (Metres)                           (Newtons)

Levers are sometimes used to lift things. Imagine putting the end of a crowbar under a crate and pushing down on the crow bar to lift up one side of the crate.

• The point at which the crow bar touches the floor is the Pivot
• The force used to push on the crow bar is the Effort
• The crate is the Load
1 of 7

## Balanced Moments

It is possible for two Aplied Forces and two Perpendicular Distances from the pivot to be involved with moments.

For a moment to be balanced the Anti-clockwise monent and the Clockwise moment have to be the same. This is an example of the Principle Moments.

This is explained in the below rule and diagram:

Sum of all anti-clockwise moments = Sum off all clock                                                               (W1 X D1)                               (W2 X D2)

2 of 7

## Centre of mass and Stability

The Centre of Mass is the point on an object where it's weight is Concentrated.

For a hanging object when the centre of mass is directly in line with the point of suspension the object is in Equalibrium, is the centre of mass isn't in line the object is in Non-Equalibrium. A hanging object at Non-Equalibrium will swing until it is in Equalibrium.

Objects have a specific amount of Stability which means the degree that they can be Tilted before Toppling.

If you tilt an object so that the centre of mass doesn't pass its pivot, the object will Fall Back into its original position.

If you tilt an object so its centre of mass is in line with its pivot the object willBalance.

If you tilt an object so its centre of mass passes its pivot the object will toppleover.

Some things such as tractors are designed so it is hard for them to topple over

3 of 7

## Circular Motion

If you put some blue tac on the end of a string and swing it around it will move in a Circular Motion.

Any object moviing in a circular motion at a constand speed:

• Its Velocity is directed towards the Tangent of the circle
• The Velocity contantly changes direction
• The change in velocity is towards the Centre of the circle

The object is aways Accelerating towards the centre of the circle.

The force from the object to the circle is a Resultant force and is called a Centripetal force.

If an object travelling in a ciruclar motions goes too fast it will break its circular motion and travel on the tangent of the circle.

4 of 7

## Gravitational Forces and Orbiting

Gravity was discovered by Isaac Newton and is the force between any two objects.

Gravity:

• Is an Atractive force
• Increases in strength as the Mass of the two objects increase
• Decreases in strength as the Distance between the two objects increases

The gravitional force on earth is 10kg/N which is much less than the Sun as it has a heavier Mass.

The Moon orbits the Earth in the shape of a slightly squashed circle. This is called an Elliptical Orbit.

For something to orbit the sun it must travel at a specific Speed. If it travels too Slow the centripetal force will overpower it and it will spiral Into the sun. If it travels too Fast it will spin Out of orbit.

5 of 7

## Satellites

When satellites are launched they have to go at the rights speed. If a satellite is launched too slow then it will Crash back to earth. If it goes to fast then it will go too far and orbit Too Far Away and each orbit will take too long.

The Further satellite is from earth the Longer each orbit takes. When a satellite completes an orbit of earth is is claled a Period.

GPS satellites are lanched from the Ground or from a Space Vehicles. They send Signals back to earth to pin point our Locations and to see where we are going.

We have Two main uses for satellites:

• Communication Satellites have a period of 24 hours, the same as Earth, so they stay over the same spot on earth. These satellites are called Geostationairy
• Monitoring satellites are fitted with cameras for Weather Forecasting and surveillance purposes. They have a period of 2-3 hours that goes from Pole to Pole so the whole earth can be monitored
6 of 7

## Galaxies and Gravity

There are Billions of Galaxies. Ours was formed 13 Billion years ago by the Big Bang.

At first our galaxy was just a hot ball of Radiation and Matter but its temperature fell and it became cold apart from Stars, the Sun is one of the Billions of stars in The Milky Way.

Andromeda is the nearest galaxy to the Milky Way.

The Dark Age was when the universe Expanded and became Transparent. Radiation passed through the empty space this caused Background Microwave Radiation.

The universe was just a Dark Empty space full of Helium and Hydrogen but then Stars and Galaxies formed which Lit Up the universe.

Due to gravity Matter in space Clumped together and became Denser which eventually formed Stars and Galaxies.

7 of 7