FORM 2 CHAP 7 Dynamics

FORM 2 SCIENCE CHAPTER 7 DYNAMICS 1. Forces a. Is pulling or pushing, twisting, hitting, pressing or lifting on an obj...

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FORM 2 SCIENCE

CHAPTER 7 DYNAMICS

1. Forces a. Is pulling or pushing, twisting, hitting, pressing or lifting on an object. b. Force can: i. Stop a moving object. ii. Move a stationary object. iii. Change the speed / direction. iv. Change the position of an object. v. Change the size/shape. c. Force cannot change the mass of an object.

iv. Therefore, work done in lifting is greater /harder than pushing.

c.

i. Air pack – move freely as the layers of air reduce the friction between the air pack and the surface. eg. Hovercraft. ii. During rainy day, the car swerves easily on the wet road because the layers of water reduce the friction between the tyres and the road surface.

2. Types of forces

a. Frictional Force i. Opposes the motion of an object when two surfaces in contact / rubbing each another. ii. Has direction and magnitude. iii. The magnitude of the friction

force is influenced by: - The weight of the object (the heavier the object, the greater the frictional force). - Condition of surface (the rougher the surface, the greater the frictional force). iv. Do not influenced by the - base area of contact - direction of movement.

b.

i. Lifting is to overcome bigger gravitational force ii. Pushing is to overcome smaller frictional force iii. Gravitational force is greater than frictional force.

d.

COMPARISON i. Advantages of ii. Disadvantages Friction of Friction - Enable us to walk - Wear tear of without slipping. possessions such as shoe sole. - enable the ladder to - cause heavy lean against the wall. objects to move slowly. - Helps vehicles to - Produce move/stop - Helps us to unwanted heat / hold/rotate to an sound waste of object. energy. - Enables nails to be - Damages or held in wood. scratch surfaces. - Enable monkey to - Reduces climb on the tree. efficiency of a machine.

e. Ways to reduce friction i. Use lubricants, grease, powder ii. Use rods, wheels and ball bearings. iii. Use air cushion, eg. Hovercraft. iv. Sprinter swimmer wears body fit sport attire. f. Ways to increase the friction WWW.ANDREWCHOO.EDU.MY

i. pattern on shoe soles ii. pattern on the tyres g. Gravitational Force i. Is the force of attraction that pulls all objects towards the centre of the Earth (like falling apple to the ground). ii. When carry an object, more force is used to overcome the greater gravitation force. (When pulling or pushing an object, lesser force is used to overcome the smaller frictional force.) h. Electrostatic Force (positive and negative charges) i. Is stationary electric charge due to rubbing of two different insulators. ii. Like charges will repel and unlike charges will attract. iii. Charged object can attract neutral object such as small pieces of papers. i. Magnetic Force i. Attraction and repulsion due to magnet. ii. Like poles repel, while unlike poles attract. iii. Magnet attracts metals such as iron, steel, cobalt and nickels. 3. Work Done a. Work done is when a force moves an object to a distance b. Work = Force × Distance (Joule) (Newton) (Metre) c. Work is not done when pushing a wall as there is no motion / movement / distance.

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