4.5.4 Moments, levers and gears

moment

turning affect of a force

examples of moments

wheel barrow

seesaw

crane

how to calculate moment of a force

*moment of a force* = *force* × *distance* 

*M*=*Fd*

moment of a force, *M*, in newton-metres, Nm force, *F*, in newtons, N

distance, *d*, is the perpendicular distance from the pivot to the line of action of the force, in metres, m.

clockwise moment

person on right applies moment acting in clockwise direction

anticlockwise moment

person on left applies moment acting in clockwise direction

equal moment

forced x distance applied by clockwise moment = force x distance applied by anticlockwise moment

what is equilibrium

sum of anticlockwise momemnts = sum of clockwise moments

why objects topple

a block on a flat surface

weight of the block (force due to gravity) acts directly down from the centre of mass

when block is tilted

there comes a point where the line of action of the weight lies outside the base of the object

now there’s a resultant (Unbalanced) moment acting on the block causing the block to topple

examples of levers

a hammer being used to remove a nail

crowbar being used to lift a plank of wood

they both transmit the turning effect of the force from one side of the pivot to the other

what is a lever

a force multiplier

they both transmit the turning effect of the force from one side of the pivot to the other 

allows us to lift a heavy object by applying a relatively small amount of force

examples of gears

in machines

cars

what are gears

transmit the turning effect of a force

second gear will always turn in the opposite direction

what does position of pivot effect

if input an output force are on different sides they will act in different directions

if input and output force is on the same side they’ll act in the same direction

why is output force closer to the pivot

produces a larger output force

with a relatively small input force

what is the turning effect of gears dependent on

the distance between the edge of the gear and the centre

If connected to a gear with fewer teeth (i.e. a smaller gear)

 The second gear will turn faster 

But with less force

In opposite direction to first gear

 If connected to a gear with more teeth (i.e. a larger gear)

o Turns slower

o More force

o Inopposite direction

how geas work

gear A (smaller gear) connected to the engine providing it with a turning force so it rotates

gear B (larger gear) connected the the wheels if gear b rotates the wheels will rotate aswell

because gears are interlocking any rotation of gear A will cause gear B to rotate as well

the gear system allows the turning effect of the engine to be transmitted to the wheels

points about gears

gears rotate in opposite directions

gear b 2x larger than gear a- meaning turning affect of gear b is 2x bigger than gear b

gear a has too rotate 2x for each rotation of gear b

so total work done is the same