Momentum

What are Newtons 3 Laws?

* Newtons 1st Law = An object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force
* Newtons 3rd Law = when 2 objects interact they exert equal and opposite forces on each other
* Newtons 2nd Law = the net resultant force acting on an object is directly proportional to the rate of change of momentum and is in the same direction
* F = kp/t (k=1)
* F = p/t = mv-mu/t = ma
* F=ma is a special case of newtons 2nd law where mass is constant

What are the 4 types of interaction?

* Strong nuclear and weak nuclear
* very short range and so little impact on things we observe in daily life
* Gravitational
* Electrostatic repulsive
* E.g. contact forces like pushing or pulling

What is momentum?

force x velocity (kgm/s)



* Conservation of momentum = for a system of interacting objects, the total momentum in a specified direction remains constant so long as no external forces act on the system (its a closed system)

Why is momentum conserved?

Newtons 3rd law says that 2 objects exert an equal and opposite force on each other and so the resultant force is 0 and so p/t = 0 and so the change in momentum of the system must be 0 and therefore momentum is conserved

What is Impulse?

product of average force \*\*\*\*and time of contact for a collision



Ft = mv-mu (impulse = change in momentum)



Ns or kgm/s



Area under F-t graph= impulse = change in momentum

How do you do calculations for collisions in 2D?

* linear momentum is conserved so to find final momentums when the objects bounce off in different directions can draw vector triangles (triangle will close)
* momentum in x and y direction is conserved so can treat separately and use trig for calculations