# Physics P3 Higher Tier (part 1)

Revision cards for part one of AQA Higher Tier part one (moments, centre of mass, stability, balence, planets and satellites

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• Created by: T
• Created on: 26-05-10 19:40

## Moments

Formula:

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

For the moment to increase one of these must happen:

• The force is increased
• The perpendicular distance to the pivot is increased
• ﻿

Apply it!

• It's easier to undo a wheel nut with a long spanner than with a short spanner
• Kitchen scissors for cutting chicken bones are longer than paper cutting scissors
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## Centre of Mass

For any object, the mass can be thought to be concentrated at one point, which is called the center of mass

Here's how to find the center of mass for a thin, laminar (flat) object:

• Suspend it from a pin at any point on the object
• Hang a plumbline (length of string with weights on the end) on the same pin
• Draw a line on the object parallel to the plumbline
• Repeat this- where the line cross is the center of mass
• ﻿

Apply it!

• You can only balence a ruler on your finger from one point on the ruler
• On a ship, the place you are least prone to get seasick is as far down as possible (the center of mass)
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## Stability

The line of action of the weight acts through the center of mass

The below properties make an object more prone to topple:

• A center of mass outside the object
• A center of mass towards the top of the object
• A narrow base

The better the stability, the further it can tip before it topples

Apply it!

• Wine glasses have a thin neck, but a wide base
• Often, in double decker buses, the bottom level must be full before passengers are allowed on the top level
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## Balence

If an object is in equilibrium when it is balenced

Formula:

Balenced object: Anticlockwise moment (Nm) = Clockwise moment (Nm)

Apply it!

• On a seesaw, the two people have to be the same weight or change where they are sitting for it to be balenced
• With old-fashioned weights, you add the weights on one side and the weighing material on the other side until it's balenced
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## Circular Motion

When an object moves in a circle, it's always accelerating, this acceleration is called Centripetal acceleration and always acts toward the center of the circle

If the centripetal acceleration stopped, the object would fly off on a tangent

Centripetal acceleration affects the direction, but not the speed and it increases if:

• The mass of the object increases
• The speed of the object increases
• The radius of the circle decreases
• ﻿

Apply it!

• A hammerthrower's stone keeps circulating him/her until they let go
• A racing car going at a fast speed in a tight circle will feel an automatic turn around the circle
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## Gravity

Every body in the universe attracts every other body in the universe with gravity, though it's often too small to notice

Gravity increases if:

• One or both of the bodies increase in mass
• The distance between the two bodies decreases

This is why, in space you weigh much less than on Earth, whereas your mass stays the same

Apply it!

• You are constantly attracted to the Earth
• As airoplanes gain altitude, their engines need slightly less power
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## Planets

Planets in the Milky Way orbit the Sun in an ellipse (squashed circle), due to centripetal force provided by gravity

The planets move at a specific speed, a specific distance from the Sun so that they continue to orbit it

The further away a planet is from the Sun:

• The slower it orbits the Sun
• The further it has to go
• The longer it takes to orbit the Sun

Apply it!

• If you whirled a stone on a string around you, a long piece of sting, moving slowly would take longer to circle you than a rapid moving short piece of string would
• We take a year to orbit the Sun, whereas the Moon only takes a month to orbit us
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## Satellites

Geostaionary satellites take one day to orbit us, as they are constantly above one place on the equator, about 36000km above Earth and can be used for:

• Communication, including recieving and sending TV and radio signals
• Space research

Low polar satellites take a few hours to orbit us and cover the entire Earth everyday, they circle us over both poles and are used for:

• Monitoring, including climate, weather and activity (i.e. spying)

Apply it!

• All satellite dishes in the Northern hemisphere point South, Southern ones point North
• On weather channels, you can often see pictures of upcoming weather
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where is part two ?

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i second this^^

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Our P3 is alot harder than this!

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