| 1. |
Extending
materials
- The extension of a spring and any other
elastic material is proportional to the stretching force,
provided the elastic limit is not reached. This is known
as Hooke’s Law.
- If the elastic
limit is not passed, elastic materials return to
their original shape and size when the stretching force
is removed. If the elastic limit is passed, the materials
remain permanently deformed.
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| 2. |
Pressure
in gases
- The pressure from a gas is caused by the
bombardment from its tiny, fastmoving molecules.
- At constant temperature, the pressure
(p) of a gas is inversely proportional to its volume (V).
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| 3. |
Work, force
and distance
Work is done when a force makes something
move.
Force is measured in Newtons (N).
Work is measured in joules (J).
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| 4. |
Power
- Power is the rate of working.
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| 5. |
Newton’s
Laws of Motion
- When an object rests on the floor, its
weight exerts a downward force on the floor. The floor gets
compressed by this force and pushes up on the object. The
two forces are balanced.
They cancel each other out, so the object does not move.
- This is an example of Newton's
First Law of Motion which says:
' An object will remain stationary or continue to move at
the same speed and in the same direction if the overall
forces on it are balanced.'
- When an unbalanced
force acts on a moving object, it will either accelerate
or
decelerate (negative acceleration). This is summarised in
Newton's Second Law of
Motion which says:
' The acceleration of a moving object is directly proportional
to the unbalanced force acting on it and inversely proportional
to its mass.'
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| 6. |
Falling objects
- When an object starts to fall, its weight
is much greater than air resistance and so it experiences
an unbalanced downward force. On the Earth, all objects
fall with an acceleration of about
when there is no air resistance (drag).
- As the object falls faster and faster,
air resistance increases. Eventually, the air resistance
will balance the gravitational forces due to the object's
weight. The forces acting on the object are now balanced.
The overall force is therefore zero, so the object falls
at a steady maximum speed. This is called the terminal velocity.
- Weight is the force of gravity on an
object.
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| 7. |
Energy
- Energy enables humans and machines to
do work.
- When objects are raised to a higher level,
they gain potential energy
(gravitational potential energy).
- Moving objects also have energy. This
is called kinetic energy.
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