Normal Force

The normal force (N) is the component of the contact force that is perpendicular to the surface that an object contacts.

When an object is placed on another, the electrical repulsion between the atoms of their surfaces prevents an object from going through the other one. The macroscopic result of these interactions is the normal force acting perpendicular to the separation surface between the two objects. The following figure represents this force, as well as the weight acting on the vase if it is close to the surface of the Earth.

In this example, as the vase has no acceleration, the forces acting on it (normal and weight) must have the same magnitude and opposite directions, but this is not a general result that can be extrapolated to other situations.

Remember that the normal force IS NOT the weight reaction.

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Newton’s third law states that a force and its reaction must be forces of the same type and must act on different objects. That’s why the normal force is not the weight reaction. The first is a contact force and the second is a gravitational interaction. Both forces act on the same object (in the example of the figure, the vase). The reaction of a normal force is another normal force and the reaction of a gravitational force is another gravitational force.

The value of the normal force depends on the problem being solved and is determined using Newton’s second law.

The normal force is very important in Structural Engineering. In this area, the reactions exerted by each element of a construction or mechanism are analyzed in order to understand what are the loads supported by the elements of the structure.

Here you can find Newton’s laws problems.

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