Question

if you place a brick on a smooth floor you can move it easily by pushing it with your feet. Yet if you kick the brick, you will hurt your foot. WHY?

Answer 1

When a brick is kicked by a person ,time for which the force impacted is short. Therefore, rate of change of momentum of the brick is large. So,a large reaction force is applied back by the brick on the foot.
so, force hurt our foot.