Walking without slipping requires a static friction force between your feet (or footwear) and the floor. As described in this chapter, the force on your foot as you push off the floor is forward while the force exerted by your foot on the floor is backward. what about your other foot, the one moved during a stride? What is the direction of the force on that foot as it comes into contact with the floor? Explain.

Upward.

Explanation:

Frictional force will prevent you from slipping while walking on the floor. However for the other foot that is moved during a stride, there is a contact force. And the floor is exerting that contact force on the foot in the upward direction while foot exert it on the floor in downward direction when it comes in contact with the floor. That's how we balanced ourselves while walking, running etc. Contact force is also known as the normal force and this force exists wherever the two objects got into contact with other. It's example can be a book on a table, box on the floor, man standing on ground is due to contact force.