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Summary GCSE Physics (AQA) revision notes for forces, energy and motion
Detailed and colourful revision summary of the topic with key equations
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Moments Centre of MassThe turning effect of a force This is where the weight of an object acts
from.
Moment (Nm) = force (N) x perpendicular distance (m)
The lower the centre of mass the more stable
Levers are a common example of moments. Moments
the object is and the greater the contact area
can be clockwise or anticlockwise and if the
or base of an object, the more stable.
anticlockwise and clockwise moments are equal the
object is balanced. This is because the lower the CoM the smaller
the perpendicular distance so when a force is
Simple levers applied the resultant moment will be smaller
Act as a force multiplier to increase the amount of force so the object is less likely to topple. The
you can apply to accomplish a task. This allows you to bigger the base the more force is needed to
move a very big load with little effort push the object so that the line of action of
the weight is outside the base, passed the
Not all levers act as force multipliers some reduce the pivot.
effect of a force such as fishing rods to avoid damaging
the object.
Hydraulics
Hydraulic systems use liquids to transmit and multiply
forces because liquids are virtually incompressible unlike
gases e.g. air and are used in braking systems in cars.
Pressure (Pa) = force (N) / area (m2)
A small force on a large area is a small pressure whereas
a large force on a small area is a large pressure
Gears
When pressure is exerted on a liquid the pressure
exerted acts in all directions Transfer the moment of a force (or torque) –
they transmit and multiply moments - and can
change the speed of the turning mechanism.
They can also change the axis of rotation.
Small
Moment small : moment large = teeth small : teeth
force
Big force large = radii small : radii large
V small : V large = teeth large : teeth small ( flipped!
Because bigger gears turn slower)
Pressure is the force acting per unit of
area so each m2 of slave cylinder will Power = force x velocity or moment x velocity
experience a force of 20N
Atmospheric pressure
Pressure in a fluid
Atmospheric pressure is
Pressure (Pa) = height (m) x density (kg/m3) x gravitational field strength (N/kg) created by air molecules
Pressure increases with depth in a liquid or gas because the pressure depends on colliding with a surface.
The atmosphere gets less
the weight of the fluid above.
dense with increasing
This explains upthrust. When an object is placed in a fluid the pressure on its altitude and pressure
bottom is more than the pressure on its top so there is a net upwards force equal decreases with an
to the weight of the water that the object has displaced which depends on the increase in height
objects volume. An object will sink if its density is more than that of water (1). because there are less air
molecules.
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