Physics - 9.6-9 - Moments (forces and their effects)

moment

turning force

Nm

cause objects to rotate/turn

Equilibrium

no resultant force acts on object

not accelerating

stationary/constant speed

net movement on object = 0

so... no rotation

principle of movements

at equilibrium, sum of clockwise moments must equal sum of anticlockwise movement (balanced moment)

Lever

bar that pivots around a point and is used to transfer a force

used as force multipliers

lever advantage

person exerts small 'effort' on one end of rod and can lift heavy load due to position of pivot

lever disadvantage

large lever means that effort moves through a large vertical distance to life the load through a small vertical distance

conservation of energy

cog

wheels with teeth to turn gears

gears

series of cogs which can

• speed up rotation with reduced moment

• slow down rotation with increased moment

large cog drives small cog 60 teeth - 30 teeth

small cog

• rotates in opposite direction

• twice the frequency

• half the moment

• half the teeth, half circum/radius

so, smaller cog rotates twice when large cog rotates once

small cog drives large cog 20 teeth - 80 teeth

large cog

• rotates in opp direction

• frequency x4 slower

• x4 teeth so x4 circum/radius

• x4 moment

so, large cog rotates once when small cog rotates 4 times

how to reduce unwanted energy transfer

lubrication

e.g. oil/greases

reduce friction on moving parts of gear, less efficent

friction

force

transfers KE into TE

reduces useful KE in a gear, less efficient

moment equation

Moment = force x distance

DISTANCE FROM FORCE TO PIVOT