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Rotational Speed

Teacher/Instructor Matt Jones
Matt Jones

M.Ed., George Washington University
Dept. chair at a high school

Matt is currently the department chair at a high school in San Francisco. In his spare time, Matt enjoys spending time outdoors with his wife and two kids.

The speed at which an object rotates or revolves is called rotational speed. Unlike linear speed, it is defined by how many rotations an object makes in a period of time. The formula for rotational speed is Rotational speed = rotations / time but linear speed = distance / time.

Okay let's talk about rotational speed, rotational speed really has 2 components. One of them is linear speed which is also called the tangential speed and that's basically the distance, the object is moving over time okay. If it's going around in a circular orbit if we released it from that orbit it would continue to move tangentially from that point in a specific speed okay. The other speed an object has is rotational speed, rotational speed is the number of rotations per time. So let's look at an example, something you'll often be asked is let's say we have 2 points on the record and the record is spinning in certain speed like 33 revolutions per minute okay. Well if we compare the speed of those 2 objects it's very different if we're talking about the tangential or the linear or tangential speed versus the rotational speed right. So if we look at them both they both have a rotational speed of 33 revolutions per minute.

But if we look at the speed that they're moving on the record the linear speed right we can see that the linear speed is actually related to the radial distance versus the rotational speed. So if I say that a is x and b is 2x in terms of our radial distance, the distance in terms of the radius from the center right we can see that b is going to be moving much faster than a. So this is why 2 objects can have the same rotational speed but very different linear speeds.