Anyone remember the old wooden "merry-go-rounds" in the playgrounds? The little kids would be on them having a good time and then the big kids would come and get them going at warp speed. A few tiny ones went flying off and cracked their heads. No more merry-go-rounds.
Or being on the seesaw, way high in the air, when the other person abruptly gets off the other end of the seesaw. Ouch.