Priyanka Devan
Updated on

The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other is known as friction. There are different types of friction which includes dry friction, fluid friction, lubricated friction, skin friction, internal friction.

  • The force that opposes the relative lateral motion of two solid surfaces in contact is known as dry friction. Dry friction is subdivided into two types. The first one is static friction  which is between non-moving surfaces, and the second one is kinetic friction which is between moving surfaces. Dry friction generally arises from the interaction of surface features, known as asperities.
  • The friction between layers of a viscous fluid that are moving relative to each other is known as fluid friction. 
  • The case of fluid friction where a lubricant fluid separates two solid surfaces is known as lubricated friction. 
  • The component of drag, the force resisting the motion of a fluid across the surface of a body is known as skin friction.
  • The force resisting motion between the elements making up a solid material while it undergoes deformation is known as internal friction.
friction on differnt object

When surfaces in contact move relative to each other, the friction between the two surfaces converts kinetic energy into thermal energy. This property can be shown by the use of friction created by rubbing pieces of wood together for making a fire. Kinetic energy is converted to thermal energy, for example when a viscous fluid is stirred. Another consequence of many types of friction can be wear. This leads to performance degradation.

Friction is  important in supplying traction . Mostly vehicles rely on friction for acceleration, deceleration and changing direction. Sudden reductions in traction can cause loss of control and this leads to several accidents.

Friction is not  a fundamental force. Dry friction arises from a combination of inter-surface adhesion. It is also due to the surface roughness, surface deformation, and surface contamination. It is a non-conservative force  also the work done against friction is path dependent. Some kinetic energy is always transformed to thermal energy, in the presence of friction, so mechanical energy is not conserved.

Standing motion

Dry Friction

It occurs between two surfaces in contact. It always acts in the direction which opposes the relative motion of the contact surfaces. This distributed force  can be represented as a concentrated friction force. It can hold the object in equilibrium. It cause it to accelerate or decelerate.

Fluid friction

fluid motiom

It occurs between fluid layers that are moving relative to each other. The above  internal resistance to flow is named viscosity. The viscosity of a fluid is described as its thickness. Real fluids offer some resistance to shearing and thereby they are viscous. 

Examples of Fluid Friction

  • When there is a wet surface between two thin glass plates developed, you can notice that plates get stuck. Thereby the bottom plate doesn’t fall when you hold only the top one.
  •  The splash is depended on the fluid friction, if  any object is dropped in a fluid
  •  Lighter dust will move faster on the surface of a flowing river. It is due to the high-velocity gradient at the top layer of water and due to lower dynamic fluid friction at that layer


The fluid friction where a fluid separates two solid surfaces is known as lubricated friction. It is a technique employed to reduce wear of one or both surfaces. In most cases the applied load is carried by pressure generated within the fluid. It is due to the frictional viscous resistance to motion of the lubricating fluid between the surfaces. Suitable lubrication allows smooth continuous operation of equipment. Moreover there will be only mild wear, and without excessive stresses or seizures at bearings. When lubrication breaks down, metal or other components can rub destructively over each other. It causes heat and possibly damage or failure.


outer skin

The friction that arises from the interaction between the fluid and the skin of the body is known as skin friction. Skin friction is directly related to the area of the surface of the body that is in contact with the fluid. Skin friction obeys the drag equation and it rises with the square of the velocity.

It is caused by viscous drag in the boundary layer around the object. Skin friction can be reduced in two ways. The first is to shape the moving body so that it makes the flow smooth, like an airfoil. The second method is to decrease the length and cross-section of the moving object.

Internal Friction


The force resisting motion between the elements making up a solid material while it undergoes deformation is known as internal friction.

Plastic deformation in solids is an irreversible change and it is  in the internal molecular structure of an object. This change may be due to an applied force or a change in temperature or both. If the shape of an object change then it is called strain and the force causing it is called stress.

Elastic deformation in solids is reversible change and it is in the internal molecular structure of an object. Stress does not always cause permanent change. When deformation occurs, internal forces oppose the applied force. When the applied stress is not too large then the opposing forces may completely resist the applied force. This allows the object to assume a new equilibrium state and to regain to its original shape when the force is removed. This is known as elasticity or elastic deformation.

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Check your knowledge

Friction is the force that opposes the motion of a solid object over another. There are mainly four types of
friction: static friction, sliding friction, rolling friction, and fluid friction

Friction is caused due to the irregularities on the two surfaces in contact. Even the smoothest surfaces have
minute irregularities in them and these irregularities of the two surfaces interlock into each other and create friction.
Larger the irregularities more is the friction.

The frictional force between two bodies depends mainly on three factors: (I) the adhesion between body surfaces
(ii) roughness of the surface (iii) deformation of bodies

Professor David Tabor is called the father of friction


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