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Contact force
 
 
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In physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
, a contact force is a force between two objects (or an object and a surface) that are in contact with each other. This is distinct from a non-contact force
Non-contact force

A non-contact force is any force applied to an object by another body that is not in direct contact with it. The most common example of a non-contact force is gravity....
 (a force that acts over a distance), such as gravity or magnetic
Magnetism

In physics, magnetism is one of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic fiel...
 attraction/repulsion.

A contact force has two components. The part of the force that lies within the plane
Plane (mathematics)

In mathematics, a plane is a curvature surface. Planes can arise as subspaces of some higher dimensional space, as with the walls of a room, or they may enjoy an independent existence in their own right, as in the setting of Euclidean geometry....
 of contact is friction
Friction

File:Friction alt.svgFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact....
, which must be overcome for the two objects to slide relative to one another along that plane.






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Encyclopedia


In physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
, a contact force is a force between two objects (or an object and a surface) that are in contact with each other. This is distinct from a non-contact force
Non-contact force

A non-contact force is any force applied to an object by another body that is not in direct contact with it. The most common example of a non-contact force is gravity....
 (a force that acts over a distance), such as gravity or magnetic
Magnetism

In physics, magnetism is one of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic fiel...
 attraction/repulsion.

A contact force has two components. The part of the force that lies within the plane
Plane (mathematics)

In mathematics, a plane is a curvature surface. Planes can arise as subspaces of some higher dimensional space, as with the walls of a room, or they may enjoy an independent existence in their own right, as in the setting of Euclidean geometry....
 of contact is friction
Friction

File:Friction alt.svgFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact....
, which must be overcome for the two objects to slide relative to one another along that plane. The part of the force that is perpendicular to the plane of contact is called the normal force
Normal force

In physics, the normal force 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....
. Friction is proportional to the normal contact force, and the constant of proportionality is denoted by µ.

Strictly speaking, contact forces are only a useful simplification for introductory physics classes and other applications of classical mechanics
Classical mechanics

Classical mechanics is used for describing the motion of macroscopic objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars, and galaxies....
. Everyday objects on Earth do not actually touch each other; rather contact forces are the result of the interactions of the electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
s at or near the surfaces of the objects (exchange interaction
Exchange interaction

In physics, the exchange interaction is a quantum mechanical effect which increases or decreases the Expectation value of the energy or distance between two or more identical particles when their wavefunctions overlap....
).

Example


An example of contact force commonly encountered in college-level physics is the force between two masses A and B which are lying next to each other and a force F is being applied on one of the masses, for example A. In such a case, the contact force will be proportional to the mass of B.

It can be assumed that the force has two components, one which is giving A an acceleration 'a' and the other which is making B accelerate with the same value of acceleration 'a'. If B>A, then the component of total force F acting on B, or the value of contact force, will be greater than when A>B.