AQA Unit 3 Physics


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The Turning Effect of Forces
Forces have a turning effect. They tend to make objects turn around a fixed point called a pivot or a fulcrum. The
turning effect of a force about a pivot is called its moment.
Moment (Nm) = force (N) x perpendicular distance from pivot (m)
The perpendicular distance is basically the distance from the pivot to the line of force. It has to be
900 for the correct value.
An object will be in balance if:
Sum of anticlockwise moments = sum of clockwise movements
Centre of Mass
The centre of mass is the point where the whole of the weight of the
object appears of act. It can be found by drawing lines of symmetry (if the
object is rectangular or symmetrical) and finding the point which all the
lines intersect, or, for an irregular shape, by suspending it freely by a
point on its edge and using a plumb line to indicate the space directly
vertical to the point. The centre of mass is always vertically below the
pivot so you can work out the centre of mass by drawing a point
somewhere in the middle of the plumb line, or suspending the object at
different points on its edge and finding out where all the lines intersect.
Objects with a low centre of mass and a wide base are stable as it is
difficult to knock over.
Parallel Forces Acting on a Plane
That's basically using the principle of moments (clockwise moment = anticlockwise moment) to find out whatever
the question asks.
Forces Acting on a Beam
The upward forces on a light beam, supported at its ends, vary with the position of a heavy object placed on the
For example(s):

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When waves strike a straight or flat barrier:
Angle of incidence = Angle of reflection
Note that the red line is called the normal line.
When waves strike a concave
barrier, they converge.
When waves strike a convex
barrier, they diverge.
Refraction is the change in direction when waves
enter a medium. The length of the waves is altered but
the frequency isn't. When waves hit shallow water,
they'll slow down and bend towards the normal.…read more

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The opposite of this is a real image. The image produced in a mirror is the same
distance behind the mirror as the object is in front of it. It is also laterally inverted. This means when you raise your
left hand, your mirror image raises his right hand.…read more

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Sound Waves
Sound waves are longitudinal waves that travel through gases,
liquids and solids. They travel slower in air, at around 340m/s and
faster in solids. Sound waves cannot travel in vacuum. Sound
waves can be reflected, refracted and diffracted.
Frequency Range for Humans: 20Hz ­ 20 000Hz (hertz)
Measuring the Speed of Sound
1. Stand 50m away from a large, blank wall and clap wood blocks. Listen for an echo.…read more

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Magnets and Electromagnetism
Magnets repel and attract other magnets, as well as magnetic substances. Like poles repel and unlike poles
Hard magnetic materials are `hard' to demagnetise ­ and are used for making magnets and other things that we
want to stay magnetised. Such materials include steel.
Soft magnetic materials demagnetise easily and are used in things like
relays and electric motors. Such materials include iron.
Magnetism can be induced into certain alloys, compounds and metals.…read more

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Note: In magnetism, when pointing towards the direction of the current, you do it, the `convectional current' way ­
as in current flows from positive to negative (I don't know why but yeah).
The Motor Effect
There is a force on a charged particle when it moves in a magnetic field as long as it
is not parallel to the field. Since an electric current is a flow of electrons ­ which are
charged particles, we can see this effect.…read more

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Electromagnetic Induction
Motors use electricity to produce movement. Generators do the opposite. When we move a wire across a magnetic
field at right angles, a voltage is induced. If the wire is part of a complete circuit, a current flows. This is called
electromagnetic induction.
It can be increased by:
Moving the wire more quickly
Using a stronger magnetic
Coiling the wire
You can also induce voltage by pushing a magnet into a coil.…read more

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