# Center of Thrust in Relation to Center of Mass

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The center of thrust in relation to the center of mass is the point where pressure performs in a very specific way. Find out about the center of thrust in relation to the center of mass with help from an applied physics professional in this free video clip.

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## Video Transcript

Hello, my name is Walter Unglaub, and this is "center of thrust in relation to center of mass." The center of thrust, which I'll just denote as C sub TH, is the point at which an object feels the average pressure from all of the pressure that is applied to the surface of that object. So, if I consider a rocket that has some trajectory in the air, it has thrust, so it's moving through the air with some trajectory, it will have a center of thrust which is equal to the point on the rocket where it feels the average pressure from the air. As the rocket's moving through the air, it feels pressure against pushing against it, and we want to understand the relation of where that center of thrust is compared to the center of mass. The center of mass is the point in or on the object where the weight around that point is equally distributed. So, as a general rule of thumb, if we have a cylindrical rocket with a cross section of diameter D, then if the center of thrust is on the order of a diameter's worth of distance away from the center of mass, then we can have a stable flight for our rocket. And, this stability will be induced by the air currents that are passing on the sides of the rocket, and applying pressure towards it. If we didn't have this relation, then the rocket could start spinning because an object will spin and freefall about it's center of mass, so that's why it's important to have a center of thrust that is somewhat behind the center of mass, so that you can stabilize a trajectory of a flying object, such as this rocket. My name is Walter Unglaub, and this is "center of thrust in relation to center of mass."

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