# Physics P3 - Revision Cards

Revision cards containing everything you need to know for AQA Physics P3

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• Created by: RATM33
• Created on: 15-01-10 17:57

## Centre of Mass (1)

How to find the Centre of Mass on a thin sheet of material

1.) A small hole is made in the material

2.) A plumb line is suspended from the hole

3.) Wait til the sheet stops moving

4.) Draw the plumb line

5.) Repeat 2,3,4

6.) The Centre of Mass is where the two lines cross

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## Centre of Mass (2)

The Centre of Mass is the point at which the mass of a body is thought to be concentrated

The centre of mass of a symmetrical shape (body) is along the axis of symmetry.

Factors that affect Stability

• A wide base (stable)
• A narrow base (unstable)
• A low centre of mass (stable)
• High centre of mass (unstable)

If the line of action falls outside thebase of the body, the object is NOT stable as there is a resultant moment and will topple over.

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## Moments

A moment is the turning effect of a force

Force x Perpendicular Distance = Moment

(Newton) N x (metre) m = (Newton metre) Nm

----

If the object is NOT TURNING, the anticlockwise moment must be balanced by the clockwise moment

Anticlockwise Moment = Clockwise Moment

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## Factors that affect the size of a moment

Example - 3N x 4m = 12Nm

1.) The Penpendicular Distance from the pivot - the greater the perpendicular distance, the greater the size of the moment

3N x 10m = 30Nm

2.) The size of the Force applied - the greater the force applied, the greater the size of the moment

10N x 4m = 40Nm

3.) To get the maximum moment from a given situation, the force needs to be at right angles to the pivot (perpendicular distance). Pushing at any other angle means a smaller moment as the perpendicular distance between the line of action and the pivot is smaller

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## Circular Motion

Velocity is speed, with a given direction

Newtons First Law - "If an object continues in a straight line at constant velocity, all forces acting on the object are balanced."

If a body moves in a circle, the forces acting on it are not balanced, it is constantly changing direction

When a body moves in a circle, it continuously accelerates towards the centre of the circle

This acceleration changes the direction of the motion of the body, not the speed.

The resultant force is called the centripetal force

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## Factors that affect the Centripetal Force

The centripetal force increases as -

1.) The mass of the body increases

2.) The speed of the body increases

3.) Theradius of the circle decreases

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## Gravity

The Earth, Moon and Sun and all other bodies are gravitationally attracted to each other

The bigger the masses of the body, the bigger the gravatational attraction

As the distance between two bodies increases, the gravitational attraction between them decreases

The further the object, the greater the time taken for the object to complete the orbit

Gravitational force provides the centripetal force that allows planets and satellites to maintain their circular orbits

To stay in orbit, the satallite must move at a particular speed.

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## Satallites

There are 2 types of satallite orbits -

Geostationary

• Above the equator
• High
• Takes 24 hours to complete
• Uses - Communications (Telephone,TV etc)

Low Polar Orbit

• Over Poles
• Low
• < 6 hours
• Uses - weather, spying, observations of the earth
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## Light and Plane Mirrors

Light is an electromagnetic wave that travels in straight lines until it is either reflected or refracted

When light strikes a plane (flat) mirror, it is reflected -

There is an incident and reflected ray;

The angle of incidence and the angle of refraction are measured from the normal line;

The normal line is a construction line that is at 90 degrees to the surface of the mirror.

The angle of incidence = angle of reflection.

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## Images

There are two types of images that you need to know about -

REAL IMAGE

• Formed when real light rays intersect to from an image
• Represented by a solid line

VIRTUAL IMAGE

• Formed when virtual rays intersect to form an image
• Represented by a dotted line
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## Describing Images

To describe an image, you need to -

1.) Say how BIG it is compared to the object

• Magnified (Bigger than the object)
• Diminished (Smaller than the object)

2.) Say whether it is the RIGHT WAY UP

• Upright (the right way up)
• Inverted (Upside down)

3.) Say whether it is REAL or VIRTUAL

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## Curved Mirrors

There are 2 types of Curved Mirrors -

Convex

• Curve OUTWARDS
• Shiny on the outside
• DIVERGES light

Concave

• Curve INWARDS
• Shiny on the inside
• CONVERGES light
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## Points on a Curved Mirror

Centre of Curvature (C)

Uniformly curved mirrors are like a round portion of a sphere. The centre of the sphere is the centre of curvature.

Vertex

The centre of the mirrors surface

Focal Point (F)

Halfway between C and the vertex

Axis

The line down the centre of the mirror - C, the vertex and F lie on this

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## Concave Mirror - Ray Diagrams

1.) An incident ray parallel to the axis will pass through the focal point when reflected

2.) An incident ray that passes through focal point will be parallel to the axis when reflected

3.) An incident ray that passes through the C is reflected back

Lines you need to draw for the exam -

• Parallel to axis --> reflected through focal point
• Passes through C --> reflected back
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## Concave Mirrors - Images (1)

Between F and Mirror -

• Upright
• Virtual
• Larger than object

At F -

No image formed as reflected rays are parallel

Between C and F -

• Inverted
• Real
• Larger than object
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## Convex Mirrors - Images (2)

At C -

• Inverted
• Real
• Same size as object

Beyond C -

• Inverted
• Real
• Smaller than object

USES -

Make Up Mirror (between F and Mirror)

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## Convex Mirrors - Ray Diagrams

1.) An incident ray parallel to the axis will pass through the focal point when reflected

2.) An incident ray that passes through focal point will be parallel to the axis when reflected

3.) An incident ray that passes through the C is reflected back

Lines you need to draw for the exam -

• Parallel to axis --> reflected through focal point
• Passes through C --> reflected back
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## Convex Mirrors - Images

At any point

• Virtual
• Upright
• Smaller than object

USES -

Shop security mirrors

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## Lenses

All lenses change the direction of light rays by refraction

Light is refracted when is enters and leaves glass prisms

The ray bends towards the normal as it enters the denser medium

It bends away from the normal as it emerges into the less dense medium

Light can be split up into the different wavelengths of the spectrum in a prism

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## TBC

...

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Report

nice - i look foward to it being contined :) i was acctually enjoying myself reading your notes :)

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nice - i look foward to it being contined :) i was acctually enjoying myself reading your notes :)

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These are pretty good - thanks. :)

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thanks : )

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that was really good, thanks:D

i listened to the mp3 aswell as reading...it helps!:D

x

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Orange Beard (Abel)

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allah

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is it meant to be concave mirror (2)? not convex mirror (2) on page 16? thanks

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thanks, these notes are very useful and concise :)

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why is the mp3 really weird.....it does not speak clearly or properly??

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these are actually not good? they're pretty **** tbh. :/

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very resourceful

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very resourceful

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Gosh this has helped me a lot and hope everyone the best on Monday for Physics. :)

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Beth Chater wrote:

You are not very nice if you did not like it then don't use and stop commenting like some kinda know it all because if you were you were not really going to use it.

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