The first thing we did in  forces was pushing and pulling.  If you jump you come back down because gravity pulls you down. Gravity only pulls you. When we push a swing gravity slow it down.

Magnets push and pull.

We leaned that some things we thought would float actually sunk.  Some things we thought would sink actually floated.  We learned that if the plasticine was a boat shape then it floated.  If it was in a ball shape then it would sink.

---