Unit 3 Physics Notes

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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
Moments
A moment is the turning effect of a force.
Even if the forces acting on a body are balanced in the sense that they do not cause
the body to change speed, they can still make the body turn.
moment = force x perpendicular distance between line of action and pivot
(Nm) (netwons) (metres)
To get the MAXIMUM MOMENT you need to push at RIGHT ANGLES to the spanner.
Pushing at any other angle means a smaller moment.
This is as the perpendicular distance between the line of action and pivot is smaller.
The centre of mass of a body is that point at which the mass of the body may be
thought to be concentrated.
If suspended, a body will come to rest with its centre of mass directly below the
point of suspension.
The centre of mass of a symmetrical body is along the axis of symmetry.
If a body is not turning, the total clockwise moment must be exactly balanced by the
total anticlockwise moment about any axis.
If the line of action of the weight of a body lies outside the base of the body, there
will be a resultant moment and the body will tend to topple .
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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
Balance and Stability
If the total anticlockwise moments do not equal the total clockwise moments, there
will be a resultant moment, so the object will turn.
Unstable objects tip over easily.
The position of the centre of mass is very important.
Most stable objects have a wide base and a low centre of mass.
Take for example a bus...…read more

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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
Circular Motion
A body remains stationary, or keeps moving at the same speed in a straight line,
unless an unbalanced force acts upon it.
If a body moves in a circular path there must constantly be an unbalanced force
acting upon it.
Velocity is both the speed and direction of an object.
If an object is travelling in a circle, it is constantly changing direction.
This means it must be accelerating.…read more

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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
The centripetal force on a vehicle moving round a roundabout is due to friction
between the tyres and the road.
The centripetal force on an aircraft circling round is due to the combined effect of its
weight and the lift force on it. The centripetal force is the resultant of these two
forces.…read more

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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
· This means Hydraulic systems are used to make difficult jobs easier to do!
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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
The Eye
Light enters the eye through a thin transparent layer called the cornea. This protects
the eye and focuses the light onto the retina. This is a layer of light sensitive cells
located at the back of the inside of the eye.
Iris: A coloured ring of muscle that controls the amount of light entering the eye.
Aqueous Humour: Transparent watery liquid that supports the front of the eye.…read more

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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
The normal human range of vision is 25cm to infinity. The eye has a near point of
25cm and a far point at infinity.…read more

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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
Eye Problems
· A person with short sight can see close images clearly, but distant objects are blurred
because the uncorrected image is formed in front of the retina. Short sight is caused
by the eyeball being too long or the eye lens being too powerful. Short sight mat be
corrected using a diverging lens.…read more

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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
Lenses and Refraction
Lenses are usually made from glass or
plastic.
All lenses change the direction of light
rays by REFRACTION.
Light is refracted when it enters and
leaves glass prisms.
Different lenses produce different kinds of image.
There are two main types of lens ­ CONVERGING and DIVERGING.
A converging lens is convex­ it bulges outwards.
o It causes parallel rays of light to converge to a focus.…read more

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EXAM:
Wednesday 20th
May [PHYSICS UNIT 3 REVISION NOTES]
The distance from the lens affects the image...
For diverging lenses...
An incident ray parallel to the axisrefracts through the lens and travels in line with
the focal point .
An incident ray passing towards the focal point refracts through the lens and travels
parallel to the axis.
An incident ray passing through the centre of the lens carries on in the same
direction.…read more

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