# √√ Mass Dilation | Space | Physics

Published on Dec 2, 2019
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√√ Mass Dilation | Space | Physics

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The Conservation of Momentum

Momentum is a quantity that is conserved in collisions.
According to the principle of relativity, momentum must be conserved in all inertial frames of reference.
Let’s look at an elastic collision between two fast-moving spacecraft.

The first postulate of relativity states that the laws of physics are the same in all inertial frames of reference.

Two Spacecraft

Suppose two equal-mass spacecraft approach each other at high speed, on each side of a ling, straight string.
When they collide, they move away from the string at the same speed (let’s say 10 m s-1), due to the conservation of momentum.

A Stationary Frame of Reference

In a frame of reference moving with one of the spacecraft, momentum in the x-direction is conserved, assuming the collision affects mostly the y-velocity.
If this frame of reference is moving at 0.6 c relative to the first frame, its measurements of time, and hence speed, will differ.

This increase in momentum is called mass dilation.
As a particle gets closer and closer to c, it gets harder and harder to make it accelerate!

Observing Mass Dilation

More simply, fast-moving things have more momentum than you’d expect.
This can be observed in particle accelerators.
Protons in the Large Hadron Collider act like their mass is thousands of times heavier than their rest mass.

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