p10 - forces and motion

what is terminal velocity 

the maximum velocity something reaches when falling

what effect does terminal velocity have on the weight

at terminal velocity the weight of an object = frictional forces acting on it

what is the resultant force when an object is moving at terminal velocity

0N

what happens in terms of energy transfers when a vehicle is braking

kinetic energy store gets transferred to thermal energy store

a larger deceleration means what for stopping distance

takes more distance to stop

what can very large deceleration lead to

brakes overheating and loss of control as well as possible injuries

how can injuries happen when braking

as a larger force is needed to stop the car it acts on the person too during the sudden brake

safety features in a car

• airbags
  - cushions to reduce force
  - seatbelt

what does a seatbelt do to stop you from getting injured

• slightly elastic
  - holds you from flying around car
  - increases time it takes for the person's deceleration

what do airbags do to stop you frm getting injured

• cushions reduce force
  - increases time it takes to decelerate ( passenger)

how do car safety features work (equation)

F = change in acceleration / time. higher time = lower force = less injuries

what is newton's 2nd law

force is directly proportional to the rate of change of momentum

what is stopping distance compromised of

thinking distance + braking distance

thinking distance definition

The time taken to react to hit the brakes

what is a typical car speed

20m/s

what is braking distance dependent on

• mass of car
  - speed before braking
  - tire tread
  - conditions of road
  - brake pad condition

thinking distance formula

speed x reaction time

momentum formula

mass x velocity

momentum unit

kg m/s

if objects collide and stick together what does that mean for the mass in a calculation

it is the mass of both objects added together

Equation of law of conservation of momentum

m₁v₁= - (m₂v₂)

Properties of the momentum of two objects post collision:

They have equal and opposite momentum

Law of conservation of momentum

total momentum before collision = total momentum after collision

Impact Force Equation:

F = m ( v - u ) / t

what affects thinking distance

• fatigue
  - under influence of drugs or alcohol
  - distractions (phone)

Newtons 2nd Law (momentum)

Net force is directly proportional to the rate of change of momentum

Main use of car safety features

Increases time of collision, therefore decreasing impact force

Air bags use

Allows passenger to slowly sink into them rather than harshly ( bc its filled with fluid)

Seat belts use

slightly elastic, allows energy/force to be dissipated over larger area

Cycle helmets

Cushioned inside, hard outside to withstand impacts

How do these saftey features help in terms of momentum

decreases rate of change of momentum

how dyk if an object us elastic

if it returns to originial shape after a force deforming it is removed

hooke's law

the extension of the spring is directly proportional to the force applied

elastic potential energy formula

Ee  = 1/2ke²

what does the overall force depend on in a collision

• mass
  - change of velocity
  - length of impact of time

what happens when 2 vehicles collide

• they exert equal and opoosite force on each other
  - total momentum is unchanged

impact force = ?

change of momentum / time

what is the intertia of an object

its tendency to stay in rest or in uniform motion

what is newton's second law formula

F = ma

the greater the resultant force on an object the greater the what

the acceleration