# What is a fidget spinner’s actual speed, in km/h?

How fast can a fidget spinner spin? Is it not that fast or can you literally use it as a car wheel?

Inspired by Matt Parker, who listened to the sound and worked the speed out from the sound frequency, Simon came up with his own method:

It just so happens that our phone has a 960fps slow-motion camera, so I recorded my fidget spinner spinning as fast as I could make it spin with my finger. There are probably ways to make a fidget spinner go faster (like by using compressed air, which is what Matt Parker did), but as an approximation of what speed the spinner normally reaches, this is a good way to do it. I then looked at the frame where it’s in position 1 and then position two 120° further. Those frames were 30 frames apart. So it must have taken 90 frames to complete one full rotation. That means it rotates 1/90th of the way every single frame. Because of the frame rate, this means it rotates at 960 x 60 / 90 = 640 RPM.

I wanted to convert that to a phyiscal speed, just for fun, so I measured the radius of the fidget spinner (4cm), and I multiplied that by 2π to get the circumference. I then multiplied that by the RPM to get the speed, and I got approximately 9 km/h. That’s not a car’s speed, but it’s still impressive it can get to my running speed 🙂