Everything about Normal Force totally explained
In
physics, the
normal force (or in some books
N) is the component, perpendicular to the surface of contact, of the
contact force exerted by, for example, the surface of a floor or wall, on an object, preventing the object from entering the floor or wall. In a static situation it's just enough to balance the force with which the object pushes, for example its weight on the floor, or a smaller force if somebody leans against a wall. If an object hits the surface with some speed, the normal force provides for a rapid negative acceleration, depending on how flexible the floor/wall is (and, of course, if it can provide enough force for stopping the object instead of breaking). Also, if the object is soft, only the outer part needs to decelerate rapidly, the inner part can do that more gradually, while the layer in between is compressed.
In general, the magnitude of the normal force is the projection of the
surface traction,
T, in the normal direction,
n, and so the normal force vector can be found by scaling the normal direction by that force. The surface traction, in turn, is equal to the dot product of the unit normal with the
stress tensor describing the stress state of the surface. That is,
»
Frictional force
The parallel
shear component of the contact force is known as the
frictional force (
).
Example
In a simple case such as a 40 kg object resting upon a table, the normal force on the object is equal but in opposite direction to the gravitational force applied on the object for example the
weight of the object. In this case the normal force is given by, 40 kg · 9.81 m/s
2=392.4
newtons where 9.81 m/s
2 is equal to the
acceleration due to gravity (near the Earth's surface).
Real-world applications
For a person standing in an elevator moving with constant velocity (including stopped), the normal force on the person's feet balances the person's weight. In an elevator that's accelerating upward, the normal force is greater than the weight and so the person's apparent weight increases (making the person feel heavier). In an elevator that's accelerating downward, the normal force is less than the weight and so a user's apparent weight decreases. If a user were to stand on a "weight scale", such as a conventional bathroom scale, onto the elevator, the scale would read either more or less than the person's actual weight when the elevator is
accelerating up or down (respectively) because weight scales measure normal force (which varies as the lift accelerates), not gravitational force (which does not).
Further Information
Get more info on 'Normal Force'.
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