force and motion- CH10

newtons second law

resultant force- mass x accelerationthi

a non-zero resultant force in the direction of motion causes

acceleration

a non-zero resultant force in the opposite direction to motion causes

deceleration

inertia

tendency of an object to stay at rest or continue at a constant velocity

inertial mass =

force/ acceleration

weight=

mass x acceleration to gravity

terminal velocity

the velocity an object reaches when falling, the weight is equal to the frictional force on it

thinking distance

distance the car travels after seeing the object and reacting, directly proportional to speed

braking distance

distance travelled in the time it takes to fully stop safely, directly proportional to speed ^2

stopping distance

thinking + stopping distance

thinking distance =

avg speed x time

braking distance=

s = v^2- u^2 / 2a

friction

between tyres and road or between wheels are break pads

braking force

f= ma

closed system

has no external forces , momentum is conserved during a collision according to the principle of momentum

momentum=

mass x velocity

collisions going the same way

take the total momentum for each car and add together for the overall momentum

head on collisions

minus the momentum for each car to find the overall

impact force

during a collision between 2 vehicles they exert equal and opposite forces on eachother

impact force =

mass x change in velocity/ time

impact time

time for the force to affect the object

acceleration=

change in velocity/ time

safety helmets

increase impact time therefore reducing impact force

seat belt

stops the wearer continuing forwards and spreads the forces across their chest, decelerating force is reduced

air bags

spreads impact force over the body and increases impact time

crumple zones, side impact bars and collapsible steering wheels

reduce the impact force

an object is elastic if it returns to its orignal shape when

the forces deforming it are removed

extension =

extended length- original length

hooke’s law

the extension of a spring is directly proportional to the force applied, as long as the limit of proportionality isn’t exceeded

hooke’s law =

force applied = spring constant x extenstion

inertia

tendency for an object to stay at rest or in constant motion