# Momentum

by on February 5, 2011

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Momentum. Image Credit: Wikimedia User Kucharek

Momentum is the quantity that shows how energy is concerved in a system. In classical mechanics momentum is described as the vector quantity that is the product of mass and velocity. Just like the conservation law energy momentum is not lost but just transferred. The most famous demonstration of momentum is Newtons Gravity Swing. A series of balls are hung from a frame with only the outer most ball being lifted and allowed to swing down. When it strikes the others the ball hanging between it and the ball at the other end remain still while the momentum transferred moves the ball on the other end.

This example is pretty simplistic but it shows in real time how momentum is conserved in a system. Like other conservation laws momentum can only be completely conserved in a close system. Otherwise it is simply transferred somewhere. Another way to describe momentum is as the conservation of motion or specfically the conservation of mass in motion. It is also important because it strongly linked with Newton’s laws of motion concerning inertia. The reason that an object in motion tends to stay in motion is because of its momentum.

Momentum as mentioned before is not a direct value of an observable phenomenon like velocity or speed. It is a vector quantity depending on the combination of two direct independent variables in order to be understood. Also like most vectors momentum not only has a magnitude, it also has a direction. The concept of momentum has major consequences when it comes to space exploration. A space craft has two unique challenges when looking to travel great distances in space. The first is that it reaches a high velocity. The second obstacle is to slow it down so it can safely land at its destination. The main problem for scientists at the moment is that it takes a lot of fuel to speed up a craft then slow it down upon arrival. A great understanding on momentum and its real world implications are vital to finding ways to make high speed space travel viable for missions in the future like a landing on Mars.

We have written many articles about momentum for Universe Today. Here’s an article about angular momentum, and here’s an article about conservation of momentum.

If you’d like more info on momentum, check out these articles from The Physics Classroom and Physics 24/7.

We’ve also recorded an entire episode of Astronomy Cast all about Rotation. Listen here, Episode 181: Rotation.

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