1. Friction By Dr.Ajay Kumar Reader School of Physical Education, DAVV Indore

2. Definition Friction may be defined as a force which oppose or resist the movement of one body over another. Friction may be defined as a force which oppose or resist the movement of one body over another. Friction is a force which oppose efforts to slide or roll one body over another. Friction is a force which oppose efforts to slide or roll one body over another.

3. Salient Features The frictional force acts parallel to the surface of contact but its direction is opposite to that of the movement. The frictional force acts parallel to the surface of contact but its direction is opposite to that of the movement. Without friction it would be impossible to walk or run, but on other hand it increase the difficulty of moving. Without friction it would be impossible to walk or run, but on other hand it increase the difficulty of moving. The opposition of movement is necessary to perform movement. The opposition of movement is necessary to perform movement.

4. Examples There are numerous examples in sports related to friction. There are numerous examples in sports related to friction. Sometime we attempt to increase friction for more effective performance. Like using rubber sole shoes, using spikes or studs in various sports, chalks on gymnast hands etc. Sometime we attempt to increase friction for more effective performance. Like using rubber sole shoes, using spikes or studs in various sports, chalks on gymnast hands etc. Some times we attempt to decrease friction, like blades in ice skates, grease in cycles and ball bearing in skates etc. Some times we attempt to decrease friction, like blades in ice skates, grease in cycles and ball bearing in skates etc.

5. Factors Deciding Friction Friction is dependent on the kind of material making up the two bodies. Friction is dependent on the kind of material making up the two bodies. The condition of the rubbing surface. The condition of the rubbing surface. If the surface is rough, amount of friction is high and if the surface is smooth friction is less. If the surface is rough, amount of friction is high and if the surface is smooth friction is less. The force with which the surface are pressed. The force with which the surface are pressed. Heavier the body greater the force and vice versa. Heavier the body greater the force and vice versa.

6. Factors Deciding Friction The relative action between the two bodies. The relative action between the two bodies. Note: The force of friction does not depend on the area of contact of two surface. Note: The force of friction does not depend on the area of contact of two surface.

7. Types of Friction Starting Friction Starting Friction Sliding Friction Sliding Friction Rolling Friction Rolling Friction Fluid Friction Fluid Friction Water Friction Water Friction Air Friction Air Friction

8. Term Related to Friction Starting friction is always high because it is used to break the inertia of the body. Starting friction is always high because it is used to break the inertia of the body. Starting>Sliding>Rolling Starting>Sliding>Rolling Starting friction, the friction which resist the start of motion is greater than sliding friction, the friction which resist continued motion. Starting friction, the friction which resist the start of motion is greater than sliding friction, the friction which resist continued motion. It takes less force to keep something sliding than it does to start sliding. It takes less force to keep something sliding than it does to start sliding.

9. Term Related to Friction (cont) While sliding friction is less than starting friction, rolling friction is much less than sliding friction. While sliding friction is less than starting friction, rolling friction is much less than sliding friction. Traction: It is the controlled motion of one body over another for which sufficient friction is required. Traction: It is the controlled motion of one body over another for which sufficient friction is required. Skidding: It is the uncontrolled motion of one body over another which results because of lack of friction. Skidding: It is the uncontrolled motion of one body over another which results because of lack of friction.

10. Coefficient of Friction The coefficient of friction between the two contacting surface is the ratio of the force required to overcome friction or to just start the body in movement to that of the force pressing together. (Usually this force happens to be the weight of one body.) The coefficient of friction between the two contacting surface is the ratio of the force required to overcome friction or to just start the body in movement to that of the force pressing together. (Usually this force happens to be the weight of one body.) µ or C = P/W µ or C = P/W Where P =Force required to overcome friction Where P =Force required to overcome friction And W = Force pressing the body together. And W = Force pressing the body together.

11. Coefficient of Friction (cont) The coefficient indicates the starting friction ratio between two surface only. The coefficient indicates the starting friction ratio between two surface only. The larger the coefficient the more the surface press together. The larger the coefficient the more the surface press together. The smaller the coefficient the easier it is for the two surface to begin sliding over each other. The smaller the coefficient the easier it is for the two surface to begin sliding over each other. A coefficient of ‘0.0’ would indicate completely frictionless surface. A coefficient of ‘0.0’ would indicate completely frictionless surface.

12. Coefficient of Friction (cont) The equation also shows that the coefficient of friction is totally dependent upon the force holding the surface together (W) and the force needed to slide one surface over another (P). The equation also shows that the coefficient of friction is totally dependent upon the force holding the surface together (W) and the force needed to slide one surface over another (P). The coefficient will decrease as P decrease. The coefficient will decrease as P decrease. Friction is overcome by changing either the surface or the force. Friction is overcome by changing either the surface or the force.