Normal force

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Normal force is a force that manifests the tendency of two surfaces not to move into each other. In other words, it is a force that opposes the inward motion of two surfaces in contact. It acts in the normal direction (the direction perpendicular to the plane of contact) and always acts outward.


[edit] Important points about normal force

[edit] Significance of normal force

[edit] Weighing machines measure normal force

When an object is placed on a weighing machine, the machine does not directly measure the object's mass, or the gravitational force acting on it. Rather, the gravitational force creates a tendency for the object to move downwards. To balance this, the machine exerts an upward normal force on the object. By the principle of action and reaction, the object exerts a downward force on the weighing machine, and it is this force that is measured by the weighing machine.

Weighing machines placed in elevators measure different weights. If the elevator is accelerating upwards, the measured weight is greater than the actual weight, while if the machine is accelerating downward, the measured weight is less than the actual weight. An extreme case of this is free fall, where an object is falling freely, and its weight is measured as zero.

[edit] Relation between normal force and friction

The harder two surfaces are pressed against each other, the greater the possibility of friction between them:

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