Chapter 3.5 - Newton's Laws of Motion Flashcards
Newtons 1st law
A body will remain at rest or continue to move in a straight line at a constant velocity unless an external force acts on it
Newtons 2nd law
The resultant force on an object is directly proportional to the rate of change of momentum of the object and the momentum change takes place in the same direction as the force
Newtons 3rd law
If object A exerts a force on object B, then object B will exert an equal and opposite force on object A
Equation for momentum
p=mv
Rate of change of momentum
Net force
In what way is F=ma a special case of F=Dp/Dt
F=ma is F=Dp/Dt but where the mass remains constant
Conservation of momentum
Assuming that no external forces act, total momentum is always conserved
Two equation for impulse
I=Ft
I=mv-mu
How is impulse related to momentum
It equals change in momentum
Area under a force time graph
Impulse
Rules for elastic collision
Momentum conserved
Kinetic energy conserved
Rules for inelastic collision
Momentum conserved
Kinetic energy not conserved
When can F=ma not be used
When objects are travelling close to the speed of light (resulting in their mass changing)
The essence of all car crash safety features
Increasing the time that it takes for the car and passengers to change their speed. This results in a lower force for the same impulse
Impulse ( P ) = Force x time
Crumple Zone and its effects (2)
Areas at the front of the car that crumple upon impact
- Absorb some kinetic energy by deforming
- Increase the time it takes for the car to slow down which reduces the forces on the passengers
