Here’s an interesting conundrum. When you place a heavy brick on a table and leave it there, the table does no work. Sure, it has to exert a force to keep the brick up, but this force isn’t moving through a distance, so no work is done. The table will happily hold the brick there for an indefinite time.

However, if you hold up a heavy brick and keep it very still, you’re not moving the brick either (just like the table isn’t) so why do you get tired? The brick isn’t moving, but you’re clearly doing work, otherwise you wouldn’t get tired. How can this be?

What’s going on?