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# Chapter 10 - Force and Pressure Part 3

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Gravitational force, Friction & Magnetic force.

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### Chapter 10 - Force and Pressure Part 3

1. 1. Chapter 1010.2 - Forces around us
2. 2. GRAVITATIONAL FORCEGravitational force is a force of attraction that pulls the object . towards earthGravitational force is a non-contact force.
3. 3. Differences between Mass and Weight Mass Weight Amount of GravitationalDefinition matter in pull acting on an object an objectS.I. Unit Kilogram NewtonInstrument of Beam Springmeasurement Balance BalanceAn Object onEarth 1kg about 10 NThe same objecton Moon 1kg about 1.67 N
4. 4. Differences between Mass and WeightFrom the table, we can conclude that: Mass does not change , and is always the same . Weight can change , depending on its location (due to different gravitational field strength, g.
5. 5. To calculate Weight W = mgwhere W = weight (N) m = mass (kg) g = gravitational field strength (10 N/kg)
6. 6. GravityExample 1(a) A object has a mass of 5 kg.What is the weight of the objecton earth given g = 10 N/kg?
7. 7. GravityExample 1(b) If the gravitational field strength on Moon is 1/6 of Earth. What is the weight of the 5kg object onMoon?
8. 8. FRICTIONFriction is a force that opposes the . motion of an object .Friction is a contact force (Friction exists when two objects are touching each other.)Friction produces heat .
9. 9. Friction can be USEFULFriction helps us to stand and walk . (Friction prevented us from slipping and falling)Friction helps us to hold an object.
10. 10. Friction can be USEFULFriction in brakes helps us to stop . or slow down vehicles.Friction is also used to produce fire .
11. 11. Friction can be a NUISANCEFriction causes wear and tear in objects.Friction slow down moving Reduces object. efficiencyFriction produces heat . in machinary.
12. 12. Ways of Reducing FrictionUse of wheels & roller as it has less friction.Use of ball bearings . (eg. On the axles in bicycles, cars and machines)
13. 13. Ways of Reducing FrictionUse of lubricants to reduce friction. (eg. Oil and grease)Use of a cushion of air . (eg. Hovercrafts)An object having a streamline designed shape reduces friction (eg. Boats, aircraft, fish)
14. 14. MAGNETIC FORCEMagnetic force is a non-contact force.Magnets can exert a push or pull . Like poles repel . ( Push each other apart) Unlike poles attract . ( Pull each other together)
15. 15. Uses of Magnetic forces Maglev Trains (Magnetic Levitation)
16. 16. Uses of Magnetic forces Electromagnets Electric Motors and Generators