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MOTION• A change in the position of a body or system with respect to time, as measured by a particular frame of reference. Only relative motion can be measured; absolute motion is meaningless.7/28/2012 3
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INFERENCE1. A body is said to be in the state of rest when it remains in the same position with respect to time.2. A body is said to be in the state of motion, when it continuously changes its position with respect to time.3. The distance between the two places is not the same; it depends upon the path chosen.4. The shortest distance, or distance travelled along a straight line, is known as displacement.7/28/2012 4
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Motion Classification • If an object covers equal Uniform distances in equal interval of time • If an object Non- covers unequal Uniform distances in equal interval of time7/28/2012 6
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Measuring the rate of motion Speed Displacement The distance The distance travelled in one covered when second or rate of travelled along a distance travelled. straight line. Total distance travelled Total covered distance Time taken Time taken7/28/2012 7
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Rate of motion Velocity Acceleration7/28/2012 8
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VELOCITY ACCELERATIONIt is the displacement made in one It is the change in velocity of ansecond or rate of change of object per second or rate of changedisplacement. of velocity. DISPLACEMENT CHANGE IN VELOCITY TIME TIME TAKENUNIT : meter/ second UNIT : meter / second2Uniform velocity : Uniform Acceleration :Equal distance covered by a body If an object travels in a straight linein equal intervals of time and its velocity increases or decreases by equal amount in equal intervals of time, then the 7/28/2012 acceleration of the object is 9 uniform.
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GRAPHICAL EQUATION OF MOTION1. Equation for Velocity at a time v = u + at2. Equation for displacement s = ut + ½ at23. Equation for velocity at a position v2 = u2 + 2as7/28/2012 10
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Acceleration due to gravity♣ When a the body is allowed to fall down, the velocity gradually increases. Now the body is accelerated.♣ The deceleration or acceleration due to the gravitational force of earth is known as acceleration due to gravity.It is denoted by “ g”The value of “ g” is 9.8 m/s 2 7/28/2012 11
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Uniform circular motion Circular motion : An athlete runs along the circumference of a circular path or The movement of an object in a circular path Uniform circular motion : When an object moves in a circular path with a constant velocity. The magnitude of the velocity is constant at all points and the direction of the velocity changes continuously. 7/28/2012 12
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• Angular displacement : The angle covered by the line joining the body and the centre of the circle. It’s measured in radian• Angular velocity : The angular displacement in one second or Rate of change of angular displacement. Angular displacement time taken ω = θ/ t UNIT : radian / second 7/28/2012 13
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CENTRIPETAL FORCE• The constant force that acts on the body along the radius towards the centre and perpendicular to the velocity of the body.•F = mv /r2• F = mrω 2• Since v = rω7/28/2012 16
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MOTION IN LIQUIDS • When a body floats or immerses in a liquid, the pressure on the bottom surface is more than that the pressure on the top of the surface. • Due to the difference in pressure, an upward force acts on the body. • This upward force is called7/28/2012 upthrust or buoyant force.17
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Centre of buoyancy• The upward force is called upthrust or buoyant force.• The buoyant force (upthrust) acts through the centre of gravity of the displaced liquid which is known as centre of buoyancy.• The buoyant force is equal to the weight of the liquid displaced.7/28/2012 18
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Archimedes principle • When a body is immersed in fluid (liquid or gas) it experiences an apparent loss of weight which is equal to the weight of the fluid displaced.7/28/2012 19
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Relative density• Density : Density of a body is defined as the mass per unit volume of the body. Mass Volume UNIT : Kg / mRelative density : It is defined as the ratio of density of the body to the density of water.7/28/2012 21
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Laws of flotation• The weight of the floating body is equal to the weight of the liquid displaced by it.• The centre of gravity of the floating body and the centre of gravity of the liquid displaced (centre of buoyancy) are in the same vertical line.7/28/2012 22
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HYDROMETERSThere are two types of hydrometers1. The constant immersion hydrometer, in which the weight of the hydrometer is adjusted to make it sink to the same fixed mark in all liquids.2. The variable immersion hydrometer, in which the weight of the hydrometer remains the same, but the depth to which it sinks in different liquids vary.3. A common hydrometer used to test the purity of milk by noting its specific gravity is called a LACTOMETER. 7/28/2012 23
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