# Why is the radius of a circle equal to the magnitude of the velocity vector?

I watched a video on khan academy(https://www.khanacademy.org/science/physics/centripetal-force-and-gravitation/centripetal-acceleration-tutoria/v/visual-understanding-of-centripetal-acceleration-formula) it said (around 3:29) that the radius of a circle is equal to the magnitude of the velocity. I am not exactly sure how the instructor concluded this?

• Please provide an exact quote. It seems more likely that the professor said the velocity is proportional to the radius. Oct 10, 2020 at 18:13
• Here is the quote: "And we already know the magnitude of the velocity vectors is this quantity v(the speed), this scalar quantity. So the radius of this circle is v(the speed)" Oct 10, 2020 at 18:24
• Two physical quantities can’t be equal if they have different units. For example 3 meters (a possible radius) and 3 meters per second (a possible speed) cannot be compared. Oct 10, 2020 at 18:49
• @G.Smith if that is so why does the instructor say that the magnitude of velocity is equal to the radius? Oct 10, 2020 at 18:51
• Some possibilities are that you misheard, you misunderstood, the instructor doesn’t know what they’re talking about, the instructor has a very unconventional and confusing way of talking about this, the instructor simply misspoke, etc. (I have not watched the video.) Oct 10, 2020 at 18:53