Summary Edexcel GCSE Physics Topic 9 - Forces and their Effect

Moments
A moment is the turning effect of a force

Moment (Nm) = force (N) × perpendicular distance from the pivot (m)

The principle of a moment for a balanced object (an object in equilibrium) – the sum of all anticlockwise
moments is equal to the sum of all clockwise moments.


The centre of mass is a point through which the weight of
an object appears to act




Gears
Lubrication reduces friction and therefore reduces the thermal energy in a machine, increasing efficiency.

Gears – high ratio à big to small
Low ratio à small to big Gears transmit a rotation force and
motion
High gear ratio – increase speed and distance, decrease force
Low gear ratio – decrease speed and distance, increase force


Depending on how much larger the bigger gear is, it dictates how much faster the smaller gear moves.
For example, if the bigger gear has 2x the number of teeth the smaller gear moves twice as fast.


For a high gear, the driver gear has a larger diameter than the driven gear and the output is low for a
given input force.

For a low gear, the driver gear has a similar diameter to the driven gear and the output is high for a given
output force




Driven Gear is one which is meshed with the driver
gear. Driven gear rotates with the help of power source
connected to the driver gear. Driven gear should be of same
module with the driver gear irrespective of number of teeth.