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# 51145703 form-2-science-chapter-7 (1)

## on May 24, 2011

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## 51145703 form-2-science-chapter-7 (1)Presentation Transcript

• Chapter 7 Dynamic fizik-fizik.blogspot.com 1
• Content7.1 Force7.2 Measuring Force7.3 Application of Frictional Force7.4 Application of the Concept of Work7.5 Application of the Concept of Power7.6 The Importance of Force in Daily Life fizik-fizik.blogspot.com 2
• 7.1 Force fizik-fizik.blogspot.com 3
• What is force ?• Push and pull are types of fore which makes an object move• Force cannot be seen but we can see the effects of force• The effects of a force include (a) force changes the shape of an object (b) force changes the position of an object (c) force changes the speed of a moving object (d) force changes the direction of a moving object fizik-fizik.blogspot.com 4
• Types of force1. Frictional force2. Gravitational force3. Electrostatic force4. Magnetic force5. Electric force fizik-fizik.blogspot.com 5
• 1. Frictional force• Produced when two surfaces in contact with each other• It prevent an object at rest from moving fizik-fizik.blogspot.com 6
• 2. Gravitational force• The force of attraction that causes objects to falls towards the Earth fizik-fizik.blogspot.com 7
• 3. Electrostatic force• Produced when two different objects are rub against each other• Static electric charges presence• Object with like charges will repel while unlike charges will attract fizik-fizik.blogspot.com 8
• 4. Magnetic force• The push or pull force exerts by a magnet• Like poles repel while unlike poles attract each other fizik-fizik.blogspot.com 9
• 5. Electric force• Produced electric when charges (electron) flow in a conductor• It is used to light up lamps or make electrical appliances work fizik-fizik.blogspot.com 10
• 7.2 Measuring Force fizik-fizik.blogspot.com 11
• Measuring Force• A force can be measured using a spring balance• The unit of force is Newton (N)• The pointer of the spring balance will be at zero (0) when nothing is hung from the hook fizik-fizik.blogspot.com 12
• Weight Vs Gravity• The weight of an object depends on the pull of gravity• The force of gravity on the moon is only one- sixth of the force of gravity on earth• Thus, the same object will have different weight on earth and the moon fizik-fizik.blogspot.com 13
• Weight and mass fizik-fizik.blogspot.com 14
• 7.3 Application of Frictional Force fizik-fizik.blogspot.com 15
• Frictional force• Frictional force occurs whenever two surfaces are in contact with each other.• Frictional force is in opposite direction to the moving object and it is parallel to the surface.• Frictional force has direction and magnitude. fizik-fizik.blogspot.com 16
• To measure the magnitude and identify the direction of the frictional force• The block of wood is pulled with a spring balance on the surface of a table surface of table.• When the block starts moving, the reading on the spring balance represents the magnitude of the friction force. fizik-fizik.blogspot.com 17
• The advantages of friction1. Friction enables a person to walk or run without slipping.2. Friction enables a vehicles to slowed down and stop when the brake is apply3. Friction enables a ladder to lean against the wall and prevent it from sliding4. Friction enables a person to hold things steady on hand fizik-fizik.blogspot.com 18
• The disadvantages of friction1. Friction produced heat which can over heat and damage a machine.2. Friction slows down movement3. Friction wears away materials like the soles of shoes fizik-fizik.blogspot.com 19
• How to reduce friction force ?There are some ways to reduce friction, such asa) Use wheelb) Apply lubricating oil or grease between the surfaces in contactc) Use air cushion to prevents contact between two surfaced) Use the ball bearing in axles of vehicles fizik-fizik.blogspot.com 20
• Factors that effect frictional force• The rougher the surfaces in contact, the greater the frictional force acts• The heavier the object, the greater the frictional force acts. fizik-fizik.blogspot.com 21
• 7.4 Application of the Concept of Work fizik-fizik.blogspot.com 22
• WorkWork is the energy used to transfer an object from oneplace to anotherWork is said to be done when a force is able to move anobject through a distance.Examples for work done are(a) Climbing the stairs(b) Dragging a bagExamples for work not done are(a) Pushing against a tree(b) Sleeping on a bed fizik-fizik.blogspot.com 23
• Calculate work done• Measurement of work done can be calculated using formula: Work done (joule / J) = Force (Newton / N) Distance (metre / m)Example : A lady uses a force of 50 N to move a trolley over a distance of 2 meters. Calculate the amount of work done. Solution: Work done = Force x Distance = 50 N x 4 m = 100 J fizik-fizik.blogspot.com 24
• 7.5 Application of the Concept of Power fizik-fizik.blogspot.com 25
• Power• Power is the rate of doing work.• Measurement of power can be calculated using formula: fizik-fizik.blogspot.com 26
• Calculation of powerExample : A lady uses a force of 50 N to move a trolley over a distance of 2 meters in 4 seconds. Calculate the power. fizik-fizik.blogspot.com 27
• 7.6 The Importance of Force in Daily Life fizik-fizik.blogspot.com 28
• The Importance of Force in Daily Life• Without electrostatic force and electrical force, all electrical appliances would not be able to function fizik-fizik.blogspot.com 29
• The Importance of Gravity Force• Without gravitational force, all objects will be floating around the air on Earth fizik-fizik.blogspot.com 30
• The Importance of Frictional Force• Without frictional force, all objects will be moving constantly and would not be able to stop. fizik-fizik.blogspot.com 31
• The Importance of Magnetic Force• Without magnetic force, compass and appliances that use motor cannot function fizik-fizik.blogspot.com 32