## Monday, February 10, 2020

### Physics in the playground III: Crash on a spiral slide

There was a spiral slide in the playground - in fact, this spiral slide.

I sent this cart:

(remember it?) with my old phone clamped to it, down the slide. Of course, being top heavy, it turned over when it hit the first twist.

The old phone also has Science Journal on it, so I recorded it's disastrous descent. Here's the recording.

It's pretty obvious that there were two big crashes and you can probably guess where they were by looking at the top photo.

Remember that the x direction is left-right. If you were in the cart, you would have been thrown to one side when the cart hit the side of the slide but, when it flipped, you would have been on the other side and would have been thrown that way. The tracings show those spikes, first in the positive direction, and then in the negative.

The y (forward-back) tracing shows a lot of deceleration, but gravity is still working so, as soon as the cart comes away from the side, it continues it's downward acceleration.

The z direction is the direction of spin and, what might confuse some folks is that most of the acceleration is toward the center of spin. Wait and see what happens when I put the phone on a rope and spin it around my head!

A nice thing about these tracings is that they can be spread out to see details. Let's look at the second crash from the x tracing.

There's a lot of vibration happening here on the order of about five spikes per second.

This is the kind of data that engineers get when they study things like crash tests and black boxes from planes that have crashed.

We'll be looking a lot closer at these motions in future blogs. This is just a preview!

Keep in mind that I'm not crashing my new phone - the one I use for a phone - down crash courses, but it's nice to have an old smartphone that I can still use as a pocket computer. It's holding up well under the abuse, but I'm also pretty careful not to overdo it. For instance, I won't just throw it as hard as I can against a tree.

Next time, we'll see what happens when something spins around at the end of a rope. Expect g-forces.