momentum

velocity, mass and momentum

p = mv

momentum before a collision...

.... = momentum after

this is the conservation of momentum

change in momentum, force and time

force = change in momentum / time

momentum safety features

larger force means faster change in momentum

likewise, if someone's momentum changes very quickly, force on the body is greater, more likely to cause injury

cars are designed to slow people down over a longer time when they crash so longer time for change in momentum, smaller force

• AIR BAGS slow you down more gradually

• CRUMPLE ZONES crumple on impact, increasing the time taken for the car to stop

• SEAT BELTS stretch slightly, increasing the time taken for the wearer to stop. reducing forces acting on chest

moments, perpendicular distance and force

moment (Nm) = force (N) x perpendicular distance (m)

what is a moment

a moment is the turning effect of a force

find centre of gravity of flat unsymmetrical object

• suspend a shape and plumb line from the same point, wait until they are stationary

• draw a line along the plumb line

• do this again, but suspend the shape from a different pivot point

• centre of gravity = where the two lines cross

moments when object is balanced

total anticlockwise moments = total clockwise moments

when u have to take one as pivot

anticlockwise moment = clockwise moment