Understanding Causes of Motion

Edited by Tosin Emmanuel, Sharingknowledge, Jen Moreau, SarMal

A body or object moving with a uniform velocity will continue to move unless it is acted upon by an external agent. A body or object in the state of rest will continue to be at rest unless acted upon by external agent. This external agent is known as force.

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Types of Force

There are two types of force:

  1. 1
    Contact Force
    These are forces are in contact with the object which they are applied. Examples of these forces include push force, pull force, tension force, reaction force and frictional force.
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  2. 2
    Non-Contact Force/ Force Field
    These are forces whose source do not require any contact with the object they are applied. These forces create a force on the body without a visible contact. Examples of these forces include Gravitational Force (Gravitational field), Electric force (Electric field), Magnetic Force (Magnetic field) and Electromagnetic force(Electromagnetic field).
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If two slides or planes are in contact, the roughness of the planes /slides prevents them from sliding freely over one another. This is an effect of friction. Friction is defined as a force which acts at the surface of separation between bodies in contact or planes and tends to oppose the motion of one over another. There are two types of friction: Static Friction and Dynamic Friction.

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Static and Dynamic Friction

Static friction is the maximum force that must be overcome before a body can move over another. For example, imagine a block of mass on a table (with a pretty rough surface) with a force spring to one of its ends. When a small pull force is applied the spring, the mass block remains in its position. If the force is increased gradually, it will get to a certain value at which the block will just start to move, and it might start as a small displacement to the direction of the force applied or a little slide. This value is called static frictional force.

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Sliding, kinetic or dynamic frictional force is the force that must be overcome so that a body can move at a uniform speed over another body.

Using the above diagram, this principle can be well understood. Consider an object moving at a particular speed. A force reduces the speed. For the object to maintain a constant speed, a force must be applied intermittently to avoid deceleration. This force is called dynamic friction.

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Law of Friction

The Law of friction states that "Frictional force (F) is roughly proportional to the normal reaction (R) between the two surface in contact." Mathematically, the law can be represented as follows;



Where µ = co-efficient of friction

The co-efficient of friction is dimensionless.

Application of Friction

The ability of friction to impede motion is widely applicable from everyday applications to more specialized applications including:

  • Friction makes it possible to walk or stop walking.
  • Friction enables the automobile tire to make a firm grip on the road.
  • Friction is utilized in fan belt used over wheels or pulleys in machines.
  • Friction enables a screw or a nail to remain in place after been screwed or driven into position.
  • Friction allows the brake to stop the car.
  • Friction is used to manufacture machine part, and it also enables us to sharpen knife and chisels.
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Methods of Reducing Friction

  • The use of lubricants like oil, grease, air and graphite.
  • The use of balls or roller bearing.
  • The streamlining of body shapes of moving object.

Referencing this Article

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Understanding Causes of Motion. (2017). In ScienceAid. Retrieved Aug 21, 2018, from https://scienceaid.net/Understanding_Causes_of_Motion

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Article Info

Categories : Physics

Recent edits by: Jen Moreau, Sharingknowledge, Tosin Emmanuel

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