To stop a moving object, a force must act in the opposite direction to the direction of motion. For instance, if you push your book across your desk, the book will move. The force of the push moves the book. As the book slides across the desk, it slows down and stops moving. The force that opposes the motion of an object is called friction. MEANING OF FRICTION Friction is the force that opposes the motion of an object. Friction can slow down or stops any moving objects. See also FORCES INCLINED PLANE PULLEYS EFFECTS OF FRICTION What effect does friction force have on motion? \tIt opposes the motion of all objects. \tIt slows down any moving objects. \tIt counteracts the acceleration of an object. \tIt prevents surfaces from sliding against each other. \tIt causes objects to accelerate. ADVANTAGES OF FRICTION Friction plays a vital role in our daily life. Without friction we are handicap. \tIt prevents slipping while walking. \tIt stops cars from moving. \tWe cannot fix nail in the wood or wall if there is no friction. It is friction which holds the nail. \tA horse cannot pull a cart unless friction furnishes him a secure Foothold. DISADVANTAGES OF FRICTION Despite the fact that the friction is very important in our daily life, it also has some disadvantages like: \tThe main disadvantage of friction is that it produces heat in various parts of machines. In this way some useful energy is wasted as heat energy. \tDue to friction we have to exert more power in machines. \tIt opposes the motion. \tDue to friction, noise is also produced in machines. \tDue to friction, engines of automobiles consume more fuel which is a money loss. METHODS OF REDUCING FRICTION There are a number of methods to reduce friction in which some are discussed here. \t Use of Lubricants The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity. \t Use of Grease Proper greasing between the sliding parts of machine reduces the friction. \t Use of Ball Bearing In machines where possible, sliding friction can be replaced by rolling friction by using ball bearings. \t Design Modification Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes made oblong to minimize friction. See also LEVERS SAFETY AND ACCIDENTS Strategies & Activities Step: Teacher revises the previous topic Step 2: Teacher introduces the new topic. Step3: Teacher endeavors to explain all the points to the pupils thoroughly. Step 4: Teacher welcomes pupils’ questions. Step 5: Teacher evaluates the pupils. Assessment & Evaluation \tDefine friction; \tState two instance of the application of friction in daily activities; \tMention two advantages and disadvantages each of friction.