# Physics 3!

All vital information in 1 palce for triple physics (P3) !!!

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• Created by: aneesah
• Created on: 04-05-12 15:53

## Centre of mass, moments and turning effects

Moment: turning effect of force

Moment = force x perpendicular distance between line of action & pivot

Centre of mass: Point where all mass is concentrated

Centre of mass for symmetrical shape: where lines of symmetry meet

If suspended the body will come to rest with its centre of mass exactly the below the point of suspension

Finding centre of mass of thin metal sheet:

• suspend & add plumbline from that point- draw a line along plumbline
• Then repeat at different point
• Centre of mass: where 2 lines meet

Object won't turn: Anticlockwise momet = clockwise moment

X x Y = X x Y, so 12 x 2 = 6 x 4

Resultant moments- object will turn-It will easily topple over if : line of action is outside the base. Stability is increased by:

• wide bases
• low centre of mass
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## Centripetal force

Centripetal force: the resultant force causing circular acceleration

Directions always towards the centre- speed does'nt change

It increases as:

• the mass increases
• speed increases
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## Gravity & Centripetal forces of planets and satell

The sun, moon & earth are all attracted by gravity

The bigger the masses the larger the attraction

larger distance less gravitational attraction, further away the orbiting body the longer it takes for it to orbit

Orbit of planets = elipse

Gravitational force provides the cenrtipetal force that allows planets to remain in circular orbit

Satellites: -Monitoring satellites-low polar orbits, few hrs; used for spying/weather

Communication satellites- geostationary orbits above equator, 24hrs for orbit

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## Mirrors, lenses & light

Real Image can be projected on a screen but Virtual Images can't

Ray diagrams-the normal: Vertical linet

Angle of incidence = angle of relection

Magnification = Image height/object height

Describe an image by: How big it is compared to object, upright/inverted, real/virtual

Plane mirrors: Image same size as object, vitual image

Concave (Diverging lens) and convex (Converging lens):

Light enters a prism (or different medium) & refracted, bends towards normal as it enters glass, a denser medium as speed of waves changes

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