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Encyclopedia > Normal force
Fn represents the normal force.
Fn represents the normal force.

In physics, the normal force F_n (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 is just enough to balance the force with which the object pushes, e.g. 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 deceleration, depending on how flexible the floor/wall is (and, of course, if it can provide enough force for braking 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. Image File history File links Incline. ... Image File history File links Incline. ... The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density. ... In physics, a contact force is a force between two objects (or an object and a surface) that are in contact with each other. ...


Note that the sign of the calculated value will be either positive or negative depending upon whether the positive y-axis is taken to be either positive or negative.


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, Traction refers to the friction between a drive member and the surface it moves upon, where the friction is used to provide motion. ... Figure 1  Stress tensor Category: ...

mathbf{F}=mathbf{n}, F = mathbf{n}, (mathbf{T}cdot mathbf{n}) = mathbf{n}, (mathbf{n}cdot mathbf{tau} cdot mathbf{n}).

Or, in indicial notation, In mathematics, especially in applications of linear algebra to physics, the Einstein notation or Einstein summation convention is a notational convention useful when dealing with coordinate formulae. ...

 F_i = n_i F = n_i T_j n_j = n_i n_k tau_{jk} n_j.

Frictional force

The parallel shear component of the contact force is known as the frictional force (F_fr). In physics and mechanics, shear refers to a deformation that causes parallel surfaces to slide past one another (as opposed to compression and tension, which cause parallel surfaces to move towards or away from one another). ... Friction is the force that opposes the relative motion or tendency of such motion of two surfaces in contact. ...


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 i.e. the weight of the object. In this case the normal force is given by, 40 kg ยท 9.81 m/s2=390 newtons where 9.81 m/s2 is equal to the acceleration due to gravity (near the Earth's surface). In the physical sciences, weight is a measurement of the gravitational force acting on an object. ... In physics, the newton (symbol: N) is the SI unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics. ... For other uses, see g force. ...


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 is 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 is 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).


  Results from FactBites:
 
The Physics Classroom (2230 words)
The force of gravity (also known as weight) acts in a downward direction; yet the normal force acts in a direction perpendicular to the surface (in fact, normal means "perpendicular").
The perpendicular component of the force of gravity is directed opposite the normal force and as such balances the normal force; the parallel component of the force of gravity is not balanced by any other force.
The force of gravity is 1000 N and the components of this force are F-parallel = 500 N (1000 N*sin 30 degrees) and F-perpendicular=866 N (1000 N*cos30 degrees).
  More results at FactBites »


 

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