What happens when a force acts on an object?
It causes a change in momentum
A larger force means a ____ change of momentum ( and so a ____ ____ )
A larger force means a faster change of momentum ( and so a greater acceleration )
What happens to the forces and what are the likely effects if someone's momentum changes very quickly (e.g. in a car crash)?
The forces on the body will be very large, and more likely to cause injury
What are cars designed with to do what?
How does this work?
Safety features which slow people down over a longer time
The longer it takes for a change in momentum, the smaller the force
'If a car crashes it will slow down very quickly'
Explain the effects of this on energy conversion and people
A lot a kinetic energy is converted into other forms of energy in a short amount of time
This can be dangerous for the people inside
In a crash, there'll be a ____ change in momentum over a ____ ____ time, so the people inside the car experience ____ froces that could be ____
In a crash, there'll be a big change in momentum over a very short time, so the people inside the car experience huge forces that could be fatal
What are cars designed to do with kinetic energy?
Convert the kinetic energy of the car and its passengers in a way that is safest for the car's occupants
Often, how do cars convert kinetic energy in a way that is safest for its passengers?
By increasing the time over which momentum changes happen, which lessens the force on the passengers
Give 4 examples of car safety mechanisms that increase the time of momentum changes and thus lessen the forces felt by passengers
1. Crumple zones
2. Seat belts
3. Side impact bars
4. Air bags
Describe how crumple zones work (4)
Located at front and back of the car and crumple up on impact
KE is converted into other forms of energy as the car changes shape
Increases the impact time
decreasing the force produced be the change in momentum
Describe how seat belts work (3)
Seat belts stretch slightly
Some fo KE absorbed by seat belt strectching
Increasing time taken for wearer to stop
Reduces forces acting on wearer's chest
Describe what are/ how side impact bars work
Strong metal tubes fitted into car door panels
Help direct the KE of the crash away from pasengers to other parts of the car (e.g. the crumple zones)
Name 2 ways air bags increase car safety
1. Slow you down more gradually, decreasing forces acting on your body and preventing injury
2. Prevent you hitting hard surfaces inside the car
When you apply the brakes to slow down a car what is done?
Work is done
How do brakes reduce the KE of the car?
By transferring it into heat (and sound) energy
Explain how regenerative braking systems work
1. Put vehicle's brakes into reverse. Wheels are slowed by motor running backwards.
2. At same time, motor acts as electric generator converting KE into electrical energy that is stored as chemcal ernegy in the vehicle's battery
What is the advantage of regenerative brakes?
They store the energy of braking rather than wasting it
The more powerful an engine is...
...the more energy it transfers from its fuel every second, and so the faster its top speed can be.
Name the 2 ways cars are designed to reach higher speeds
1. Powerful engines
2. More aerodynamic
Define 'aerodynamic' in terms of cars
Cars shaped so that air flows very smoothly and easily past them, so minimising their air resistance
When do cars reach their top speeds?
When the resistive force (e.g. air resistance)
the driving force provided by the engine