When watching Adam Peaty win gold (for Britain) yesterday, I was interested to see his speed shown in metres per second on the second 50 metres.
From memory, it was 1.53 metres per second. So that’s 5508 metres/hour or 5.5 kph (3.4 mph). You would be hard pressed to walk at that speed let alone swim it!
A speed expressed in metres per second can help in understanding acceleration. If Adam suddenly put a superhuman spurt on (and he is probably capable of it), and 10 seconds later, he was swimming at 2.53 metres per second. his acceleration would have been 1.0 metres per second (change in speed) in 10 seconds, or 0.1 metres per second, per second.