1. ASSIGNMENT BOOK Unit 9 Part 1 9.4 A. Check your concepts Study the following statements. Put a ‘ T ’ in the box against a correct statement and a ‘F’ against an incorrect statement. T F 1.Friction is a force that opposes motion between surfaces. 9.4 Friction 2.Friction is always a hindrance in our daily lives. 3.Friction is measured in kg. F

2. ASSIGNMENT BOOK Unit 9 Part 1 9.4 T 4.Oil can be used as a lubricant. T 5.A car is more likely to skid on a wet road because the water reduces the friction between the tyres and the road.

3. ASSIGNMENT BOOK Unit 9 Part 1 9.4 D. Questions 1.The picture below shows the frictional forces (a-e) that occur when a cyclist is riding a bicycle. Match the letters to the frictional forces and decide whether it is useful or not. If it is not useful, match it with a method to reduce it. If it is useful, match it with a method to increase it.(15 marks)

4. ASSIGNMENT BOOK Unit 9 Part 1 9.4 Friction friction in the wheel bearings friction between the wheel and the brake blocks friction between the tyres and the road friction on the cyclist from the fast passing air friction between the shoes and the pedals Method to reduce it or increase it The tyre should be grooved. The pedal surface should be rough. Add some oil on the wheel bearings. The cyclist should put on tight sports wear. The blocks shoud be made of rubber. Useful or not useful ( ) a b c d e not useful useful not useful

5. ASSIGNMENT BOOK Unit 9 Part 1 9.4 2.The diagrams below show friction in action. For each diagram: (i)identify and name the two surfaces between which the friction occurs. (ii)state the effects of the friction. (iii)imagine what would happen if the friction suddenly disappeared.

6. ASSIGNMENT BOOK Unit 9 Part 1 9.4 (a)Draw on a piece of paper with a pencil (3 marks) Pencil core and paper Helps making marks on the paper. We cannot draw anything on the paper. (i) (ii) (iii)

7. ASSIGNMENT BOOK Unit 9 Part 1 9.4 (b)Remove the nail in wood with a hammer (3 marks) Nail and wood Friction holds the nail in wood. The nail can be removed easily from the wood. (i) (ii) (iii)

8. ASSIGNMENT BOOK Unit 9 Part 1 9.4 (c)Walk on a road(3 marks) Shoe and surface of the road Friction prevents us from slipping. We cannot walk or run. (i) (ii) (iii)

9. ASSIGNMENT BOOK Unit 9 Part 1 9.4 (d)Sticky tape holder on a table(3 marks) The bottom of the holder and the table top Friction holds the holder on the table As we pull the tape, the holder will move forwards. (i) (ii) (iii)

10. ASSIGNMENT BOOK Unit 9 Part 1 9.4 3.A helicopter has many ways to reduce friction. Identify them and complete the diagram.(4 marks) (a)Uses ball ______________ in wheels and axles. (b)Has a ______________ (smooth / rough) surface to reduce air friction. (c)Adds ______________ such as oil or grease to all moving parts of the helicopter. (d)Has a ______________ (long and narrow / short and wide) shape to reduce air resistance during flight. bearings smooth lubricants long and narrow