# What Is Thrust?

By Walter UnglaubThrust is a type of reaction force due to the acceleration of matter in a separate direction. Find out more about thrust with help from an experienced physics professional in this free video clip.

### Transcript

Hello, my name is Walter Unglaub, and this is what is thrust. Thrust is a type of reaction force due to the acceleration of matter in a, in the separate direction. So as an example, let's consider a rocket. The rocket is burning fuel and it's ejecting mass in this direction, and we can describe thrust in terms of Newton's second and third laws. So, from Newton's third law, a force of an object one acting on two is going to be equal in magnitude but opposite direction to the force that object two enacts on object one. So in this rocket we have thrust in the atmosphere due to the ejection of material through the burning of the oxygen fuel. So the reaction force will be described by the change in mass over time times the velocity. So, the larger this change in mass, the larger the reaction force, and of course as the velocity increases, this force will increase as well. The force that this ejection of matter will cause the rocket to go in this direction. Of course here I'm neglecting air resistance, but we see that this is a slightly different formulation then the type of force that we're used to learning about. We're used to learning about the force is equal to the constant mass times the change in the velocity over time. But here, this thrust reaction force is formulated in terms of the change in mass over time. So, we see that this is an equally valid force because it also has units of Newtons, in this case 1 Newton is equal to 1 kilogram per second times meter per second. My name is Walter Unglaub, and this is what is thrust.