As you stand on a floor, does the floor exert an upward force against your feet? How much force does it exert? Why aren’t you moved upward by this force?
The correct answer and explanation is:
Yes, the floor does exert an upward force against your feet. This force is called the normal force. Its magnitude is equal to the weight of your body, which is the gravitational force pulling you downward. In other words, if your weight is, for example, 700 newtons, the floor pushes upward on your feet with a force of 700 newtons to balance that weight.
The normal force exists because the floor is a solid surface that resists being compressed or penetrated. When you stand on the floor, your feet push down due to gravity. The floor’s atoms and molecules respond by pushing back with an equal and opposite force according to Newton’s Third Law of Motion. This reaction prevents your feet from sinking into the floor.
Despite this upward force, you are not moved upward because the forces acting on you are balanced. The upward normal force from the floor exactly counteracts the downward gravitational force on your body. Since these forces are equal in magnitude and opposite in direction, your net force is zero. According to Newton’s First Law of Motion, if the net force on an object is zero, the object remains at rest or moves at a constant velocity. In this case, it means you remain standing still rather than accelerating upward.
Additionally, your muscles and skeletal system keep you stable and prevent any motion. The floor does not push you upward with extra force beyond what is necessary to support your weight. If it did, you would accelerate upward, which does not happen in everyday standing situations. Thus, the normal force is a balancing force that supports you against gravity without causing movement.