Update 10/13/17 – Fidget Spinners in Space!
I’d heard about these fidget spinner things all the kids have and finally got my hands on one.
Now I can’t put it down.
This simple spinning toy is totally addictive. Not to mention all the science!
Here is the spinner I have – most kids have something similar.
How does it work?
The key to this engineering marvel is ball bearings. In the photo above I took off the buttons that cover the bearings in the center so that you can see what allows the toy to spin so fast.
Without the ball bearings – those tiny metal balls inside – you would have pieces sliding against each other. Just like when you rub your hands together, the friction between sliding pieces quickly turns motion energy into heat energy. But the ball bearings don’t slide, they spin and roll. Rolling friction is immensely smaller than sliding friction. This allows the toy to spin and spin and spin so very fast.
The black rings in each of the three lobes of the toy also contain ball bearings, which also spin around.
All of this fast spinning leads to pretty cool science.
See the spin
Just watching your spinning toy through a video camera leads to a crazy effect. Check out this video I made.
First, I must have been holding the spinner at an angle to the camera, which caused the bottom to look distorted and larger than the rest.
Even cooler is how the spinner appears to slow down, stop and change directions. In reality, the toy was spinning so fast I couldn’t even see the separate lobes.
The effect is caused by the video camera. Video cameras don’t actually take continuous images. Instead most cameras take 30 pictures each second. Our brains fill in the motion in between those photos so that it seems like continuous motion.
When the toy spins at 30 spins per second, the same rate as the camera takes pictures, the toy appears to slow and stop. When it spins slower than 30 spins per second it appears to move backwards. If you’ve ever watched a car race on TV you may have noticed the same effect with car wheels that appear to spin backwards.
Feel the angular inertia
It is extremely satisfying to hold this spinning, whirring toy between your fingers. Part of this is the small resistance you feel when turning the spinner from side to side. What you feel is actually the angular inertia of the spinning toy.
You are probably familiar with linear inertia, the stuff Newton described in his laws. Basically, objects moving in a straight line at constant speed will keep moving that way until a force pushes on them. If you ride in a car and it turns you might feel pushed against the door on the outside of the turn. In reality your body is moving in a straight line (that’s the inertia) and the car door (and seat and rest of the car touching you) is pushing you sideways to make you turn. You are pushing against the door to try to go in a straight line and the door is pushing back to make you turn. That’s another one of Newton’s laws – every force has an equal (sized) and opposite (direction) re-force.
The same thing works for spinning objects. Spinning objects will continue to spin in the same direction and orientation unless a force pushes on them. You push on the spinning toy to change its orientation and toy pushes back on your finger. This is what causes that satisfying resistance force on your fingers as you turn the spinner from side to side.
The angular inertia of the spinner – or its tendency to keep spinning in the same direction and orientation – allows for some pretty cool tricks or hacks.
For this you need to first pop off the buttons in the center of the spinner to reveal a hole straight through the middle. Then find a pen that fits snuggly in that hole (all of the pencils I tried were too small). Start the toy spinning and balance the pen on its tip. You will find it makes an incredibly stable top!
Try putting your top down at an angle and watch as it spins itself back to vertical. Spin the toy and then drop the top on to a table and watch it keep spinning. What else can you do with this super fast top?
Leave the pen from the spinner top in the toy. Find a piece of string or thread about 8 or more inches long and tie it tightly to the short end of the pen (the part closest to the spinner).
Hold the long end of the pen so the tip is pointed down and start the toy spinning. Hold up the end of the string and let go of the pen. You will see the pen and toy appear to float on the end of the string as it spins.
Experiment with where you tie the string, where on the pen you put the spinner and other changes to make the best floating gyroscope.
To get your spinner going super fast try using a hair dryer set on high (and cool so you don’t burn your fingers) to “blow up” your spinner.