CHAPTER 7: DYNAMIC

1. CHAPTER 7: DYNAMIC • Push and pull are types of force. • We cannot see force but we can see the effects of force. • Activities such as pushing a box, climbing, ridinga bicycle, pulling a rope involve the use of force. • Force can change the shape, position, speed, size, stop and direction of the movement of an object.

2. Not work done • Push a wall • Sit on the chair • Sleep on a bed • Read a book • Stand up

3. Type of force

5. Frictional Force (friction) • friction occurs whenever two surfaces rub against each other. Friction is a force that always oppose motion.

7. Gravitational Force (gravity) • gravitational force or gravity is the force of attraction that pulls objects towards the Earth. • The force of gravity acts equally in all objects. Thus, in a vacuum, all objects whether heavy or light will fall to the Earth with the same velocity(halaju). Viscosity - kelikatan

8. Electrostatic Force • produced by charged substances. • Are caused by the presence of static electrical charges. The electrical charges are produced when two different objects are rubbed against each other. Like charges repel while unlike charges attract. • Example, it can attract small pieces of paper, stream of water flowing from a tap.

9. Electrical force • Is produced when electrons move through a conductor placed in a magnetic field. electron flows fromnegative terminal to the positive terminal

10. Magnetic force • Are the attractive and repulsive forces exerted • by magnets. Like poles of magnets repel each other while unlike poles of magnets attract each other.

11. THE MEASUREMENT OF FORCE • The unit of force is measured in Newton (N). • Force is measured using the spring balance. • 1 N shown on a spring balance is equal to nearly 100g. (10N = 1kg) • Example, if

12. FRICTIONAL FORCE AND ITS APPLICATION. • A force which slows down moving objects is called frictional force or friction. • Frictional force can also be used to start or stop a motion. • Frictional force acts when two surfaces come into contact, sliding over each other. • Friction can at times be useful but in other instances it an also be a nuisance (GANGGUAN). • Friction is a force that opposes motion. It acts in the opposite direction to movement. • Friction always produces heat. • Friction has direction and magnitude.

13. How different types of surface affect frictional force. • Friction has magnitude and direction. • Magnitude depend on: 1. Nature surface – smooth or rough 2. Weight – light or heavy 3. Surface area not influenced magnitude of force. (big or small) • Different types of surfaces affect the magnitude of frictional force. • Rough surfaces have more friction than smooth.

14. Perlis 2012

16. ADVANTAGES AND DISADVANTAGES • Advantages of friction (friction is useful) • Friction plays an important role in our daily activities. • Friction between a piece of rough metal and a flint produces sparks. These sparks ignite the gas in a lighter. • Friction enables the mechanical belt in car engines and machines to turn engine parts. This moves the vehicle and machines. • Disadvantages of friction (friction is a nuisance). • Friction produces heat. For example, machine parts that move produce heat. This heat can damage certain parts of the machines if the machine is not carefully controlled. • Friction opposes and slows down movement. For examples ridding a bicycle up a slope or paddling a boat. • Friction wears away materials. For examples, friction wears out the soles of shoes and the tyres of vehicles.

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18. PMR 2012

19. PMR 2012

20. PMR 2012

21. PMR 2012

22. FORMULA Work is done when a force moves an object through the distance in the direction of the force. Work (Nm) = Force (N) X Distance (m) Work (J) = Force (N) x Distance (m) 1 newton-metre (Nm) = 1 joule (J)

23. test • (20 kg + 10 kg) , 2m • 10 n , 1 km (1000m) • 30 kg + 20 kg naiktangga 5 anaktangga, tinggi 5 anaktanggaialah 8 m, kira WD 15m 8 m 20 kg 10 m

24. TRY • WD (Nm) = force (N) x distance (m) • = (40kg + 5 kg ) x 10N x 4m • = (45 kg x 10N) x 4 m • = 450 N x 4 m • = 1800 Nm • = 1800 J

25. Power is the rate of doing work, that is the work done in one second (or the energy used per second).

26. Check ?

27. Selangor 2011

28. TEST 1 45 kg 7 m 8 m 10 m Calculate work done? Calculate Power if time taken is 5 s

29. TEST 2 45 kg 20 cm 8 m 20 cm 20 cm 20 cm a. Calculate work done? b. Calculate Power if time taken is 5 s 10 m

30. TEST 3 20 cm 45 kg 20 cm 8 m 20 cm 20 cm 20 cm 10 m a. Calculate work done? b. Calculate Power if time taken is 5 minute

31. Test 4 45 kg 12 m 7 m 10 m 5 m a. Calculate work done? b. Calculate Power if time taken is 5 s

32. Test 5 45 kg 12 m 7 m 10 kg 10 m 5 m a. Calculate work done? b. Calculate Power if time taken is 5 s

33. Test 5 45 kg 10 kg 10 m 5 m a. Calculate work done? b. Calculate Power if time taken is 5 s

34. wall Test 6 45 kg Era Faziratolakdinding a. Calculate work done? b. Calculate Power if time taken is 5 s

35. Test 7 SitiNurhalizapanjatdindingsetinggi 5 m. Kirakerja yang Dilakukan? wall 45 kg 5 m a. Calculate work done? b. Calculate Power if time taken is 5 s

40. The chart below shows situations when work is done and when work is not done. swimming

41. N 9 2011 Moment of force Moment of force - turning effect of a force. Moment of force (Nm) = perpendicular distance from the fulcrum to the force (m) X force (N) To increase the moment of force • Increase the perpendicular distance • Increase the magnitude of applied force Moment of force (Nm) = perpendicular distance from the fulcrum to the force (m) x force (N) Moment either clockwise or anticlockwise Tightening a nut (clockwise ) Perpendicular distance = 15 cm = 0.15 m The moment of force = 20 N x 0.15 m = 3 Nm b. Loosening a nut (anticlockwise ) Perpendicular distance = 15 cm = 0.15 m The moment of force = 20 N x 0.15 m = 3 Nm

49. Penutup 1. Baca Surah Al-`Ashr 2. Tasbih Kifarah.