eli5. What does inertia mean?


eli5. What does inertia mean?

In: Physics

If you’re being lazy, you stay lazy.

If you’re motivated, you stay motivated.

Unless something comes along and changes what’s happening, you’re going to keep feeling the same thing.

A thing that is moving keeps moving. If you want to change that, you need a force proportional to its mass and the change in movement. The tendency of the thing to go on doing the same thing it did before is inertia.

The first law of physics says that an object in space will keep its motion unless another force acts on it.

If you apply force to an object in space (i.e. throw a rock in the air) it will **theoretically** keep moving in the direction you threw it because of inertia – this means that you are not applying any more force to the rock, but the rock keeps moving in that direction indefinitely.

Obviously in real life, on Earth, there are other forces acting on the rock, so eventually the rock will start slowing down, and then fall towards the ground and stop.

Edit: spelling

Inertia is basically mass. It can be thought of as the property of a material that opposes changes to its motion, the m in F=ma. The greater the inertia, the harder it is to stop or get moving. If you imagine being in space, on the ISS for example and you have two identical suitcases, one empty and one full of rocks. If you pushed them both with the same force, the empty one will move away faster because it has less inertia. Objects in Space are apparently weightless, but not massless.

It’s all due to energy. Velocity of mass means it has kinetic energy, one half the mass times velocity squared is the energy equation. A plate just sitting on a table has no kinetic energy. It’s going to stay there unless energy is applied to accelerate it (objects at rest tend to stay at rest). And now that it has kinetic energy we are going to have to take away that energy in order to stop it (objects in motion tend to stay in motion).