Let’s talk about moving things. On Earth, we’re always on the move (or so they tell us), but we don’t feel it. There are other places, too, where we can be jetting along at, oh, hundreds of miles an hour, and not feel that, either. For example, on excruciatingly long leg-bending neck-cricking plane rides, why does it feel like you’re going nowhere?
When it comes to machines, we know that they move. We can see it and usually we can feel it. But the rules that govern that motion elude us. Take the bicycle – a brillant two-wheeled invention that translates radial motion (what your feet do) into lateral motion (the bike’s movement forward). We all know that if you sit on a non-moving bike and take your feet off the ground, you’ll tip over pretty quickly. But put that same body on the same moving bike and – voila! – you are magically one with the machine, perched easily atop it. If gravity is constant, and you weigh the same, and of course the bike is the same… why does motion change everything?
Some movements are so fast – or slow – as to defy sight and sound. A hummingbird’s flutter can’t be seen at high speeds, and glass moves so slowly that it appears stagnant, like a solid – even though it’s really an amorphous liquid. And an object moving quickly enough can break the sound barrier, which actually causes a huge bang.
Two bonus questions for mechanics aficionados:
- Can a simple pendulum oscillate in a moving satellite?
- Where will a rock hit the ground if you drop it out a moving vehicle?