Section 5 Flashcards
Newtons first law
The velocity of an object will remain the same unless a resultant force acts on it
Newtons second law
The rate of change of momentum of an object is proportional to the net force which acts on it
Momentum equation in terms of Newtons second law
F = change in momentum / change in time
Why can’t F=ma be used in all cases (at the speed of light)
The mass is changing
Newtons 3rd law
If an object A exerts a force on an object B, then the object B exerts and equal but opposite force on object A
Newtons 3rd law is consequence of what?
The conservation of momentum
A net force means an acceleration so when there’s a force on an object, the same must be returned to keep the change in momentum 0
Newtons 3rd law
The forces opposite each other are always what?
The same type
Car safety
Why are car crashes so bad
Big change in speed, so big change in momentum
Car safety
How can the general momentum be reduced?
Increase time of crash
Car safety
Crumple zones
Absorb kinetic energy which would have gone to passengers
Increase time for car to slow down to reduce force
Car safety
Air bags
Make passenger slow down more gradually
Stopping them from hitting steering wheel/dashboard
Car safety
Seat belts
Holding passenger in place
Absorbing kinetic energy
Increase time it takes to stop
Car safety
Seat belt risks
Cause bruising and dangerous for children
Car safety
Air bag risks
hit the air bag with too much force
bad for rear facing child seats
