The spinny thing on a playground is called a Merry Go Round.
Merry Go Round's are a spinny thing that can have either horses on them that you ride on such as at a fair or the merry go round can just be a spinning playground equipment device with handles on it that you spin and then get on it and go around and around.
The Merry Go Round has been a very popular playground toy and equipment and has been fun and gave many kids enjoyment over the years.
The merry go round is mounted on a bearing which is mounted on concrete.
When kids spin the merry go round around and around some try to get the merry go round to go faster and faster and then jump on it.
I remember in Kindergarten me and a friend were spinning the merry go around as fast as we could get it and he jumped on it first and made it and then I tried jumping on it myself and I missed and slid underneath that merry go round.
I cut my knee and also the merry go round was going near my face as it spun around and around and I thought I was gonna get more severely injured or die as a result.
I still however now as an adult like to go to playgrounds and hop on one of those merry go rounds as it's very fun.
I want one for my own yard one day.