P4 + Flashcards
What is the conservation of momentum?
The conservation of momentum states that the total momentum of 2 objects is the same before they interact as it was after they interacted.
What does the force on a person in a crash depend on?
- The person’s initial momentum (depends on their mass + speed of the car)
- How quickly they are brought to a stop
If the time taken to stop is increased, the force is reduced
What happens in a collision?
- In a collision, a force brings the body to a sudden stop
- The larger the stopping force on the body, the more it is damaged
- To reduce damage you must reduce the force
- To reduce the force you must increase the time taken to stop
- The time of a collision can be increased by designing cars to have special safety features
CAR SAFETY FEATURES
Crumple zones
•The front and back of the car are designed to crumple in a collision, increasing the distance and time taken over which the occupants are brought to a stop
Airbags
•The body hits the airbag, which is compressed, increasing the distance the body moves and the time it takes to stop
Helmets
•These contain a layer of material which would compress on impact so that the skull is brought to a stop slower
Seat belts
•Seat Belts are designed to stretch slightly so that the body moves forward and domes to a stop slower with a smaller deceleration than it would if it hit the windscreen or front seats
Both helmets and seat belts should be replaced after a crash as the materials would be damages an may not protect/work effectively again
What can forces do?
- Change the speed of an object
- Change the direction of movement of an object
- Change the size or shape of an object
- Keep things moving at the same speed (constant speed)
- Forces are measures in Newtons (N)
‘Up thrust’ only applies to objects in water.
‘Reaction force’ applies to objects not on water.
What is instantaneous speed?
The speed at a particular moment in time
Graphs can be use to summarise and analyse the motion of an object
E.g distance-time graphs
What is speed + velocity?
Speed is how fast something travels.
Velocity is speed in a certain direction.
To show something is going backwards you use a minus (-) sign.
What is friction?
The force when two materials rub together
What is tension?
The force when a material is stretched
What is magnetism?
The force that enables a compass to work
What is air resistance?
The force when an object moves through air
What is compression?
The force when a material is squashed
What is electrostatic?
The force between two charged objects
What is nuclear force?
The force that holds particles together in a nucleus
What is gravity?
The force of attraction between objects with mass
