Eli5: how does the self-locking mechanism on a scissor jack work?

Question

https://imgur.com/a/2THq9K3

I understand how a scissor jack can lift a heavy object, but what I don’t get is how the lock mechanism keeps it in place while letting it move whenever the crank is spun. A visual illustration would be greatly appreciated as well.

In: 2

Answer 1

To raise the jack, you’re turning a screw. In order for the jack to be lowered by force from the top, it would have to “unscrew” the screw. This takes a LOT of force.

Here’s an analogy. Say you’re screwing a bolt into a nut. It’s easy to turn the bolt with a screw driver. But if you try to screw it in by “pushing” on it, it won’t budge. The same thing is happening here.