12. Running on soft dry sand is exhausting, so you switch to running on hard wet sand. The hard wet sand removes less energy from you because
- it pushes up on your foot just as hard as your foot pushes on it, unlike the soft dry sand.
- it barely moves downward as you push downward on it, so you do almost zero work on it.
- it stops the downward motion of your foot faster and thus absorbs less of your momentum.
- it stops the downward motion of your foot faster and thus absorbs more of your momentum.