Let’s Get Physics-l: Momentum

(Please note: The characters used in the examples below are property of Marvel comics and I did not create them. I am simply using them to help convey a concept. Thank you)

Before we carry on with Newton’s Laws of Motion (As interesting as they are) we need to take a step back and get to grips with an important aspect of motion: Momentum. Linear momentum is the product of mass and velocity of an object or momentum is directly proportional to the mass of a moving object and the velocity of said object. It has the unit kgms^-1 and, as it is a product of velocity, it is a vector quantity.

Momentum, in any collision (Elastic or Inelastic) or interaction, is always conserved. Always. This effectively means that the sum of the momentum before a collision is equal to the sum of the momentum after a collision. This is incredibly helpful in calculations but first, let’s have an example.

Wolverine and the Hulk have gotten into a bit of a tussle over something stupid and have decided to sort out their differences with a good old fashioned brawl (Please note: I don’t support this sort of behaviour but it is a helpful way of explaining this). Hulk takes the first swing and catches Wolverine dead in the chest. The momentum at which Hulk’s fist makes contact with Wolverine sends Wolverine 100 metres, colliding into a rather large tree. Ouch (I like to think the little details add to the mental image). The momentum of Wolverine in flight is equal to that of the momentum of Hulk’s punch and this is because of this principle of conservation of momentum.

We can calculate momentum with a rather straight forward equation which is this:

p = mv

  • p – Momentum (kgms^-1)
  • m – Mass (kg)
  • v – Velocity (ms^-1)

We can develop this equation to then work out the change in momentum of an object:

p = mv – mu

  • v – Final Velocity (ms^-1)
  • u – Initial Velocity (ms^-1)

We can develop this further to demonstrate this idea that momentum is conserved:

m1u1 + m2u2 = m1v1 + m2v2

  • m1 – Object 1 Mass (kg)
  • m2 – Object 2 Mass (kg)
  • u1 – Object 1 initial velocity (ms^-1)
  • u2 – Object 2 initial velocity (ms^-1)
  • v1 – Object 1 final velocity (ms^-1)
  • v2 – Object 2 final velocity (ms^-1)

As you can see, momentum is pretty helpful for calculating equations concerning motion.


Summary

  • Momentum – the product of mass and velocity which it is directly proportional to.
  • Conservation of Momentum – Sum of Momentum before collision = Sum of Momentum after collision
  • P = mv
  • P = mv – mu
  • m1u1 + m2u2 = m1v1 + m2v2

That’s Momentum, a pretty awesome concept in my opinion. As always, please post any thoughts, questions, requests or feedback in the comments. Thank you.

 

 

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