Definition
Friction Force
When two rough surfaces in contact move against each other, a force is exerted between them that resists this motion. This is called friction force.
For example, when you try to push a table across the floor, friction acts between the legs of the table and the floor. This makes it difficult to push the table.
For example, when you try to push a table across the floor, friction acts between the legs of the table and the floor. This makes it difficult to push the table.
Definition
Explanation of Frictional Force
When two bodies are kept in contact, electromagnetic forces act between the charged particles at the surfaces of the bodies. As a result, each body exerts
a contact force on the other. The magnitudes of the contact forces acting on the two bodies are equal but their directions are opposite and hence the contact forces obey Newton's third law.The direction of the contact force acting on a particular body is not necessarily perpendicular to the contact surface. We can resolve this contact force into two components, one perpendicular to the contact surface and the other parallel to it (Figure). The perpendicular component is called the normal contact force or normal force and the parallel component is called friction.
a contact force on the other. The magnitudes of the contact forces acting on the two bodies are equal but their directions are opposite and hence the contact forces obey Newton's third law.The direction of the contact force acting on a particular body is not necessarily perpendicular to the contact surface. We can resolve this contact force into two components, one perpendicular to the contact surface and the other parallel to it (Figure). The perpendicular component is called the normal contact force or normal force and the parallel component is called friction.
Example
Factors that affect friction
Friction between two surfaces depends on the smoothness of the surfaces in contact. A greater force is required to move the surfaces past each other when they are rough as compared to when they are smooth.
Also, it is more difficult to move a heavier object on the ground than a lighter one where the two objects are of the same material.
Also, it is more difficult to move a heavier object on the ground than a lighter one where the two objects are of the same material.
Definition
Factors affecting fluid friction
Frictional force on an object in a fluid depends on its speed with respect to fluid and on the shape of the object and nature of the fluid.Hence birds and fishes have special shapes so that they can easily overcome fluid friction.
All vehicles are designed to have shapes which reduce fluid friction for example shape of aeroplane is spindle.
All vehicles are designed to have shapes which reduce fluid friction for example shape of aeroplane is spindle.
Definition
Effect of area of contact on friction
As shown in the given diagram area of contact of the block is different in the two diagrams but spring balance will show the same reading on pulling.
The frictional force appears the same in both cases irrespective of the area of contact of the surfaces. So, the frictional force is independent of the area of contact.
The frictional force appears the same in both cases irrespective of the area of contact of the surfaces. So, the frictional force is independent of the area of contact.
Result
Qualitative Difference Between Static and Kinetic Friction
| SI. | Static Friction | Kinetic Friction |
| Nature of Force | It is the frictional force acting between two surfaces which are attempting to move, but are not moving. | It is the frictional force acting between two surfaces which are in motion against each other. |
| Action | It acts when the surfaces are not in relative motion against each other. | It acts when the surfaces are in relative motion against each other. |
| Range | It increases linearly with the force applied until it reaches a maximum value. | It remains constant regardless of the force applied. |
Definition
Static Friction
Static friction is the force which acts between two bodies when a force is applied on a body but there is no relative motion between the surfaces. Static friction opposes an impending motion. It is denoted by . Law of static friction is given by:
where is the coefficient of static friction and depends only on the nature of the surfaces in contact. is the normal force.
Definition
Kinetic Friction
Frictional force that opposes relative motion between surfaces in contact is called kinetic or sliding friction and is denoted by . It is given by:
where is the coefficient of kinetic friction, which depends only on the surfaces in contact and is the normal force.
Example: When a wooden block is sliding on the floor the friction acting between the wood surface and the floor will be kinetic friction.
where is the coefficient of kinetic friction, which depends only on the surfaces in contact and is the normal force.
Example: When a wooden block is sliding on the floor the friction acting between the wood surface and the floor will be kinetic friction.
Definition
Static Friction
Static friction is the force which acts between two bodies when a force is applied on a body but there is no relative motion between the surfaces. Static friction opposes impending motion. It is denoted by . law of static friction is given by:
where is the coefficient of static friction and depends only on the nature of the surfaces in contact. is the normal force.
Definition
Sliding Friction
The Sliding Friction is friction which comes into play when surface of one object moves relative to surface of another object. It is also called as kinetic friction. It is that force that keeps a surface sliding with another surface. For example, if book is kept on floor and the book moves with respect to the floor.
It is the frictional force between two surfaces that are rubbing against each other. It’s hard to find a perfectly smooth surface in the real life, therefore when an object slides on any surface, it undergoes a backward force because of the relative motion between the two adjacent surfaces. It always acts against the motion.
It is the frictional force between two surfaces that are rubbing against each other. It’s hard to find a perfectly smooth surface in the real life, therefore when an object slides on any surface, it undergoes a backward force because of the relative motion between the two adjacent surfaces. It always acts against the motion.
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