What force propels the runner forward?

[JessicaHelena]

Homework Statement

A person is running on a track. Which of the following forces propels the runner forward?
a) The normal force exerted by the ground on the person
b) the normal force exerted by the person on the ground
c) the force of friction exerted by the ground on the person

2. Homework Equations

none?

The Attempt at a Solution

I had thought it was a bc since the person pushes on the ground the ground pushes back by Newton's 3rd law, but the answer is c) and I'm not quite sure why — what makes normal force and force of friction different so that only one of them propels the person forward?

 

[DrClaude]

I had thought it was a bc since the person pushes on the ground the ground pushes back by Newton's 3rd law, but the answer is c) and I'm not quite sure why — what makes normal force and force of friction different so that only one of them propels the person forward?

Draw a diagram of the running shoe on the ground with arrows representing the different forces.