The speed of a tennis ball on the return of a serve can be just as fast as the serve, even though the racket
isn't swung very fast. How can this be?

where’s the list ? the question is incomplete

heats surface water up

the only real purpose of sputnik 1 was to beat the us into space. we were getting close to launching a useful satellite, explorer 1 - which launched on january 31, 1958. the ussr had to beat that, so they launched sputnik 1 on october 4, 19