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FORCE, 1], , Differentiate between contact & non-contact force., The force applied by contact between objects is contact force., Eg. Friction, pulling a cart, pushing a trolley etc., The force applied without contact on an object is non-contact force., Eg. Magnetic force, gravitational force etc., , 2], , What is friction?, When a body moves or tends to move on the surface of another body, a force is, experienced parallel to the surface which opposes the relative motion between, them. This is friction., , 3], , State the difference between rolling friction and sliding friction?, When a body rolls over the surface of another body, the friction is rolling friction., When a body slides over the surface of another body, the friction is sliding, friction., Rolling friction is less than sliding friction., , 4], , What are the methods to reduce friction?, 1 Streamlining, 2 Lubricants, 3 Polishing, 4 Using ball bearings, , Designing shape of objects to reduce friction Eg. Shape of, an aeroplane, Lubricants are materials used to reduce friction . Eg. Oil,, grease, graphite etc., Friction can be reduced by polishing the surface., Ball bearings are used to reduce friction in machines., Principle that rolling friction is less than sliding friction is, used here., , 5], , Classify the following situations into contact and noncontact forces., a. Applying break in a bicycle., → Contact force, b. A mango falling from a mango tree., → Non-contact force, c. The earth revolving around the sun., → Non-contact force, d. The speed of a ball rolling on ground is reduced., → Contact force, , 6], , Differentiate between thrust & pressure., The total normal force acting on a surface is thrust., Thrust per unit area is pressure., 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 =, , 𝑇ℎ𝑟𝑢𝑠𝑡, 𝐴𝑟𝑒𝑎, , 𝐹, , 𝑃=𝐴
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7], , What is the unit of pressure?, N/m2 or Pa [pascal], , 8], , What is the relation between surface area and pressure?, When surface area decreases, pressure increases., , 9], In the given situation, how does the relation between surface area & pressure helps?, 1 Making a knife with sharp By sharpening, surface area of the edge is, edge, decreased and pressure at the edge increased., This makes it easy to cut., 2 Constructing buildings with By constructing wider bases, surface area of the, wider bases, base is increased and pressure is decreased. This, prevents the building from sinking into ground., 3 Connecting the wheels of By connecting chains, surface area of wheels is, tanks & other vehicle using increased and pressure is decreased. This, wide chains, prevents vehicle from sinking into the ground., 4 Making a sewing needle By sharpening of tip, surface area is decreased &, with sharp tip., pressure increased. This makes it easy for the, needle to pass through cloths., 10], , State reason, a., We are able to walk on the ground without slipping., Due to frictional force., b., It is easy to cut vegetables using a sharp knife., Lower the surface area, higher the pressure., c., The number of tyres is more for goods vehicles., Higher the surface area, lower the pressure., d., The moving parts of machines experience wear and tear., Due to frictional force, , 11], Match the following [Answer to let us assess qn. no.3], A, B, C, Atmospheric pressure bar, barometer, Lubricant, friction, coconut oil, Coconut falling down, gravitation, noncontact, Magnet, attraction, Repulsion
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12], Answer to let us assess qn. no. 5, a] The car doesn’t move, b] The car moves towards B, c] In the first case external force is balanced. Hence no movement, In the second case force is unbalanced. So the car moves., 13], , In which of the following circumstances does atmospheric pressure acts., a. Drinking Juice using a straw, b. Attraction of nail by a magnet, c. filling ink using a filler, d. paper bits get attracted to a glass rod which is well rubbed with silk, Ans: a) & c), , 14], , Give reason:, 1., Astronauts wear specially designed clothes, This dress helps to maintain the pressure between the dress and the body, equal to that of atmospheric pressure., 2., As mountaineers climb to higher altitudes there is a possibility for nasal, bleeding, As the altitude increases atmospheric pressure decreases. The higher, pressure inside the body leads to nasal bleeding, 3., Fixing rubber suckers on polished surfaces, When rubber sucker is pressed against the wall the pressure inside the, sucker decreases. Due to the greater atmospheric pressure the rubber, sucker sticks to the wall., 4., What is the unit of atmospheric pressure?, Bar, 5., Which device is used to measure atmospheric pressure?, Barometer, 6., The weight of air column over unit area of earth's surface is ......, Atmospheric pressure
