Friction : The opposing force which comes into play in between the surfaces of two bodies, when one is moved over the surface of another is called force of friction or friction.
Whenever there is a relative motion between the two surfaces in contact, an opposing force comes into play to prevent the relative motion. This opposing force is called force of friction.
When a body is at rest on a surface and no external force is applied, no friction exists. In this case the normal reaction R balances the weight Mg i.e. for vertical equilibrium R = Mg and frictional force =0
Causes of Friction : The surfaces of solid bodies are never perfectly smooth. Friction is produced by the interlocking of irregularities of one surface with that of the other surface in contact.
Static Friction : The friction offered by the surfaces in contact subjected to external forces until there is no motion between them is called static friction.
When an external force (F) is applied to move the body and the body does not move, then the frictional force acts opposite to applied force F and is equal to the applied force i.e., F – f =0 frictional force ,f = applied force F. When the body remains at rest, the frictional force is called the static friction. Static friction is self adjusting force.
Limiting Friction: The maximum value of friction which comes into play when a body just starts moving over the surface of another body is called limiting friction.
The force of friction goes on increasing as the pull on the body is increased till it just starts moving over the surface of another body.
Consider a block of wood placed over the surface of a table. When no force is applied on the block, there is no force of friction between the surfaces in contact and the block is under the action of the following two forces:
(i) Weight of the block W = mg acting vertically downwards.
(ii) Normal Reaction are acting vertically upward.
When some force is applied to pull the body, friction comes into play and the body does not move. If the pulling force is gradually increased, the force of friction also increases. When the body just starts moving or is at the verge of motion the opposing force attains a maximum value and is called the force of limiting friction. The various forces acting on the block when it just starts moving are:
(i) weight of the block W = mg acting vertically downwards
(ii) Normal reaction R acting vertically upward
(iii) pulling force F
(iv) Force of friction f acting opposite to F
Since the body is in equilibrium under these forces , we have
W = R, and F = f
i.e., Weight of the body = Normal reaction
and, pulling force (F) = Force of friction (f)
When the pulling force slightly increases the force of limiting friction, the body just start moving.
Whenever there is a relative motion between the two surfaces in contact, an opposing force comes into play to prevent the relative motion. This opposing force is called force of friction.
When a body is at rest on a surface and no external force is applied, no friction exists. In this case the normal reaction R balances the weight Mg i.e. for vertical equilibrium R = Mg and frictional force =0
No friction
Static Friction : The friction offered by the surfaces in contact subjected to external forces until there is no motion between them is called static friction.
When an external force (F) is applied to move the body and the body does not move, then the frictional force acts opposite to applied force F and is equal to the applied force i.e., F – f =0 frictional force ,f = applied force F. When the body remains at rest, the frictional force is called the static friction. Static friction is self adjusting force.
Limiting Friction: The maximum value of friction which comes into play when a body just starts moving over the surface of another body is called limiting friction.
The force of friction goes on increasing as the pull on the body is increased till it just starts moving over the surface of another body.
Consider a block of wood placed over the surface of a table. When no force is applied on the block, there is no force of friction between the surfaces in contact and the block is under the action of the following two forces:
(i) Weight of the block W = mg acting vertically downwards.
(ii) Normal Reaction are acting vertically upward.
When some force is applied to pull the body, friction comes into play and the body does not move. If the pulling force is gradually increased, the force of friction also increases. When the body just starts moving or is at the verge of motion the opposing force attains a maximum value and is called the force of limiting friction. The various forces acting on the block when it just starts moving are:
(i) weight of the block W = mg acting vertically downwards
(ii) Normal reaction R acting vertically upward
(iii) pulling force F
(iv) Force of friction f acting opposite to F
Since the body is in equilibrium under these forces , we have
W = R, and F = f
i.e., Weight of the body = Normal reaction
and, pulling force (F) = Force of friction (f)
When the pulling force slightly increases the force of limiting friction, the body just start moving.
courtesy: sciencehq.com
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