"Tump" is so a word!

I grew up in Birmingham, AL and used to have a neat playground toy in the backyard called a whirlygig.  It was a round, 4 seater, merry-go-round type thing with handles and foot pedals at each seat.  A fanny goes in each seat, hands on the handles, feet on the pedals - push, pull, spin!  Loads of fun - when you have 4 people who can make it go.  I had a little brother and a little girl neighbor and a little girl across the street neighbor; as you can see I was a giant among little children in my back yard.  Every now and then we'd have enough kids to make it go and that was like going to a carnival!  But when I was on one seat and not enough weight directly across, it would tump over.  Does anyone NOT know what I mean?  I related this story once and was soundly laughed at.  "Tump" is so a word and evokes a great bunch of memories!