The normal force is the force exerted perpendicular to the surface of contact between two objects. It is the force that acts to support an object and prevent it from sinking into or falling through the surface it is resting on.
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The normal force is always perpendicular to the surface of contact and acts to support the weight of an object.
The magnitude of the normal force is equal to the component of the object's weight that is perpendicular to the surface.
On an inclined plane, the normal force is less than the object's weight and is directed perpendicular to the inclined surface.
In uniform circular motion, the normal force acts perpendicular to the velocity and provides the centripetal force necessary for circular motion.
The normal force does not do any work on the object since it is perpendicular to the object's displacement.
Review Questions
Explain how the normal force is related to Newton's Third Law of Motion.
According to Newton's Third Law of Motion, for every action force, there is an equal and opposite reaction force. When an object rests on a surface, the object exerts a downward force (its weight) on the surface. The surface then exerts an equal and opposite upward force, known as the normal force, on the object. This normal force is the reaction force that supports the object and prevents it from sinking into or falling through the surface.
Describe how the normal force changes on an inclined plane and how this affects the object's motion.
On an inclined plane, the normal force acting on an object is less than the object's weight. This is because the normal force is directed perpendicular to the inclined surface, while the object's weight has a component parallel to the inclined surface. The reduced normal force results in a smaller frictional force, which can allow the object to slide down the inclined plane under the influence of the gravitational force component parallel to the surface.
Analyze the role of the normal force in uniform circular motion and explain how it provides the necessary centripetal force.
In uniform circular motion, the normal force acts perpendicular to the velocity of the object and provides the centripetal force necessary to keep the object moving in a circular path. The normal force is directed towards the center of the circular motion and is responsible for accelerating the object towards the center, causing it to change direction and maintain a circular trajectory. Without the normal force, the object would continue in a straight line due to its inertia, and circular motion would not be possible.
Related terms
Contact Force: A contact force is a force that arises due to the physical interaction between two objects that are in contact with each other.
Reaction Force: A reaction force is an equal and opposite force that arises in response to an applied force, as described by Newton's Third Law of Motion.