Momentum
If a body of mass m has a velocity v, then its momentum ρ is
Ρ=mv
The units of momentum are kgms¯¹ or Newton Seconds (Ns)
Momentum is a vector quantity so it has a direction.
When it comes to A2/A-level Physics, do you still remember the Law of Conservation of Momentum?
Law of Conservation of Momentum
Momentum is conserved in all collisions, explosions and interactions.
The total momentum of a system before any interaction is exactly equal to the total momentum after it provided no external forces act.
(m1u1 + m2u2) = (m1v1 + m2v2)
- When two objects collide, the changes in their momenta will be equal in size but opposite in direction.
- The momentum gained by one body equals the momentum lost by the other.
Recoil and Explosions
- Guns and cannons recoil when fired because of the law of conservation of momentum.
- The positive momentum gained by the bullet or cannon ball is equal to the negative recoil momentum of the gun or cannon, and so the total momentum before and after the explosion is zero.
Elastic and Inelastic Collisions
- Kinetic energy is conserved in elastic collisions.
- Kinetic energy is not conserved in inelastic collisions.
- Momentum is conserved in all collisions.
- Total energy is conserved in all collisions.
In inelastic collisions, some kinetic energy is converted to other forms of energy (mainly heat).
Large scale collisions are inelastic.
Collisions between hard steel spheres are nearly elastic.
Some particle collisions are elastic.
Impulse and Newton’s Second Law of Motion
- Most bodies have constant mass, so it is normally noted that un-balanced forced cause acceleration.
- Unbalanced forced cause a change in momentum.
- The change in momentum depends on the size and direction of the force and the period of time over which it is applied.
- Impulse is the product of force and time.
- Impulse = change in momentum
- Ft = mv – mu (mu is initial and mv is final momentum)
- Force = rate of change of momentum = (mv-mu)t
- Impulse is measured in either newton seconds of kgms¯¹. (Same units as momentum)
References:
1. https://byjus.com/physics/newtons-second-law-of-motion-and-momentum/
That's the end of the topic!
Drafted by Bonnie (Physics)