Pushes come in pairs

Before this sitting

Can you already do this?

Two quick checks on “you will be able to…”. Right on both and this sitting becomes mixed practice, not a lecture. Wrong is useful — we keep the full sitting.

1. You jump off a skateboard. The board rolls backward. Why?

   AThe board is lighter so it must be the only thing that feels a forceBYou pushed the board, and the board pushed you — a pair on two objectsCGravity flippedDSkateboards store leftover backward force

2. When you walk, the force that moves you forward is…

   AA force inside your legs that does not need the groundBThe ground pushing you forwardCWind in front of youDYour shadow pulling you