3.5 Newton's laws of motion Flashcards
What condition is needed for monetum to be conserved?
No external forces act
Whats a perfecly elastic collision?
Momentum and kinetic energy is conserved
Whats an inealastic collision?
Some energy is transfered into other forms durring the collsion
BUT momentum still conserved
Define impulse
Average force x Time (=change of moemtum)
What is the area under a force time graph?
F x change in T (Impluse)
State Newtons second law
The rate of change of momentum on an object is directly proportional to the net force which acts on a n object (F=change in p/ change in t)
State newtons 3rd law
If A exerts a force on B,
Then B exerts equal but opposite force on A
Explain what happens in a car crash (in terms of moentum)
Big change in speed (Like 70mph to 0mph)
So big change in momentum
so force acting on car an people inside is BIG
This can be reduced by increasing the tie the impact takes place over
How to crumple zones protect car driver?
They crumple on impact
- absorbs some of cars Ke when they deform, would usually be transferred to person
- They increase time for car to slow down, reducing force on passenger
How do airbags protect driver?
They inflate quickly on collsion
- Make passenger slow down more gradually increasing t
- stop person hitting steering wheel
How do seat belt protect driver?
They stretch slightly
- Holds person in place so not thrown about
- Absorbs some of persons Ke
- Increase time person comes to stop by stretching
What are crash tests for?
test effectivenss of safety features to see reduced injuries.
Use dummies to measure forces that passenegrs experince in deifferent kinds of collsions
What have governemnt done to improve saftey?
Seat belts mandatory, crumple zones and air bags are standard features
Risk of seatbelts?
Bruises
small kids neck injury
-so need booster seat
Air bag risks?
If not used alogside seatbelt, air bag inflates rapidly with lots of force.
And rear facing baby seats near airbag can cause child to be thrown at seat :o
