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Presentation on Friction (Static, Kinetic and Co-efficient of Friction)
- 1. Friction Md. Sirajul Islam Sagor Dept. of Textile Engineering 30th Batch Daffodil International University
- 2. • Friction is the resistance to motion of one object moving relative to another. It is not a fundamental force, like gravity or electromagnetism. Instead, scientists believe it is the result of the electromagnetic attraction between charged particles in two touching surfaces.
- 3. Friction is a “catch-all” term that collectively refers to all forces which act to reduce motion between objects and the matter they contact. Friction often transforms the energy of motion into thermal energy or the wearing away of moving surfaces.
- 4. EQUATIONS Models for friction The friction force is approximately equal to the normal force multiplied by a coefficient of friction. kinetic friction static friction rolling friction
- 5. Symbol • Ff • Units • Newtons (it’s a force!) • Depends on • Weight of object (normal force) • Nature of the surfaces between the moving object and the supporting surface
- 7. TYPES OF FRICTION • There are two main types of friction • static friction and • kinetic friction. • Static friction operates between two surfaces that aren't moving relative to each other • while kinetic friction acts between objects in motion.
- 9. If a crate is dragged to the right, friction points left. Friction acts in the opposite direction of the (relative) motion that produced it. Kinetic friction is sliding friction. It is a force that resists sliding or skidding motion between two surfaces. KINETIC FRICTION
- 10. Which takes more force to push over a rough floor? KINETIC FRICTION
- 11. The board with the bricks, of course! The simplest model of friction states that frictional force is proportional to the normal force between two surfaces. If this weight triples, then the normal force also triples—and the force of friction triples too. FRICTION AND THE NORMAL FORCE
- 12. The force of kinetic friction Ff between two surfaces equals the coefficient of kinetic friction μk times the normal force FN. direction of motion A MODEL FOR KINETIC FRICTION
- 13. LAWS OF KINETIC OR DYNAMIC FRICTION • The force of friction always acts in a direction, opposite to that in which the body is moving. • The magnitude of the kinetic friction bears a constant ratio to the normal reaction between the two surfaces. But this ratio is slightly less than that in case of limiting friction. • For moderate speeds, the force of friction remains constant. But it decreases slightly with the increase of speed
- 14. • Without static friction between your feet and the floor, you could not walk or run. Your feet would slip. Static friction is gripping friction. It is a force that prevents relative motion between surfaces in contact with each other. STATIC FRICTION • Without static friction between your tires and the road, you could not start or stop a car.
- 15. The maximum static friction force Ff between two surfaces is the coefficient of static friction μs times the normal force FN. direction of applied force A MODEL FOR STATIC FRICTION • When μs = 0 there is no friction. • When μs = 0.5 the maximum friction force equals half the normal force. • When μs = 1.0 the maximum friction force equals the normal force.
- 16. LAWS OF STATIC FRICTION : • The force of friction always acts in a direction, opposite to that in which the body tends to move. • The magnitude of the force of friction is exactly equal to the force, which tends the body to move. • The magnitude of the limiting friction (F ) bears a constant ratio to the normal reaction (RN) between the two surfaces. Mathematically, F/RN = constant • The force of friction is independent of the area of contact, between the two surfaces. • The force of friction depends upon the roughness of the surfaces.
- 17. Static friction prevents this crate from sliding when pushed . . . . . . until the pushing force is greater than the maximum static friction force available. STATIC FRICTION
- 18. The coefficient of friction is a constant that depends on both materials. Pairs of materials with more friction have a higher μk. direction of motion THE COEFFICIENT OF FRICTION
- 19. COEFFICIENT OF FRICTION • Two solid objects moving against each other experience kinetic friction. • In this case, the friction is some fraction of the perpendicular force acting between two objects (the fraction is determined by a number called the coefficient of friction, which is determined through experiments). • In general, the force is independent of the contact area and doesn't depend on how fast the two objects are moving.
- 20. That’s All…