The law of motion that explains the force you feel against the sole of your foot when taking a step forward is Newton's Third Law of Motion.

Here's why:

* Newton's Third Law: For every action, there is an equal and opposite reaction.

* Action: When you push off the ground with your foot, you are applying a force downwards and backwards.

* Reaction: The ground pushes back on your foot with an equal and opposite force upwards and forwards. This is the force you feel against the sole of your foot.

Essentially, you are pushing on the ground, and the ground is pushing back on you, allowing you to propel yourself forward.