Question

1. if you walk along the ground. what is the action in the movement?

the ground sinking under the weight of your foot.
your foot indenting because of the pressure from the ground.
your foot pushing the ground.
the ground pushing on your foot.

Explanation:

When walking, according to Newton's third law of motion (action - reaction forces), the action is the force exerted by the foot on the ground (your foot pushing the ground), and the reaction is the force exerted by the ground on the foot. The first option (ground sinking) is about deformation due to weight (not the action in the walking movement in terms of force pair). The second option (foot indenting) is a result of the ground's force on the foot (more of a reaction - related deformation). The fourth option (ground pushing on foot) is the reaction force.

Answer:

Your foot pushing the ground.