When something turns around an axis that doesn't move, we call this rotation. We see rotation all around us — a merry-go-round on a playground, a vinyl record on a turntable, even a washing machine that cleans our clothes. It can often be important — and interesting — to determine just how fast something spins. We call this rotational speed and it is measured as the number of rotations over a certain period of time. In the Olympic Games, athletes often need to rotate in order to compete in their sports. Gymnasts rotate their bodies during routines, ice skaters rotate during their spins, and aerial skier perform rotations high in the air. How do the spinning accomplishments of these amazing athletes compare to other rotating things that we know about?
Ferris wheels rotate about relatively slowly making one revolution every 600 seconds or so. A ceiling fan, on the other hand, rotates around once every two seconds. This translates into a rotational speed of 0.5 Hertz, the unit we use to talk about rotation. Hertz=# of rotations per second
That is very quick, but a gymnast doing a back flip rotates with a speed of 1.5 Hertz while an ice skater can spin with a rotational speed of 50 Hertz.
We also find things in space that rotate. For example, all of the planets, including Earth, rotate around an axis as they make they orbit around the Sun. This rotation, which happens once every 24 hours on Earth, gives us our day and night. The Sun also spins, making one rotation about every 25 days. Elsewhere in space, astronomers have found objects that rotate at a dizzying speed. For example, the dense cores left behind after stars explode — known as neutron stars — can some rotate at remarkable rates. The neutron star at the center of the Crab Nebula is moving at 30 Hertz, in other words making 30 rotations in just one second. That's almost as fast as Olympic ice skaters, which is amazing especially when you consider that the neutron star is over 10 miles or 16 kilometers across!
Perhaps the next time you watch a gymnast tumble or a skiing do a flip, think of the other examples in our lives and across space where rotation is taking place.
