As kids we had a solid understanding of many laws of physics without ever having learned them in a classroom. Imagine how dull it would have been to have had to master a knowledge of fulcrums before being allowed out on the playground. Fortunately we had the teeter-totter and figured things out quite handily.
The equipment required two children, one on each end of a long board. Each had a handle which suggested that the child would stay secured to the board. One child would go down, push her feet and the other child would go down. A problem obvious in the photo above is that the two girls are nearly evenly weighted. We could stop and ask them to solve the issue with a law of physics. Instead we could watch as one child or the other scoots forward or backward until one end goes down allowing play to continue. In the center of this particular board is a fitting that allows the board to be repositioned in three different slots. Again no lengthy discussion would ensue. A larger child intuitively knew what adjustment needed to be made to allow fun to go on.
Teeter-totters seem to have disappeared from playgrounds. Apparently some cautious adults noticed the clever explorations of the laws of physics taking place. There was the famous jump off the board while the other child was still in the air maneuver. The stranded child would land with a thump, perhaps cracking a tooth on the handle. Another mischievous variation had the one child push so hard that the other child went flying, handle or no. I assure my readers that I have only heard of these experiments and NEVER tried them myself. If you find an archaic teeter-totter, please NEVER learn physics this way.
Schools have decided that learning things in books is much safer than learning them on playgrounds. What a loss.