Consider a buggy being pulled by a horse. Which is correct?
1. The horse can pull the buggy forward only
if the horse weighs more than the buggy.
2. The force on the buggy is as strong as the
force on the horse. The horse is joined to the
Earth by flat hoofs, while the buggy is free to
roll on its round wheels.
3. The horse pulls before the buggy has time
to react so they move forward.
4. The horse pulls forward slightly harder
than the buggy pulls backward on the horse,
so they move forward.