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CHAPTER - 13, MOTION AND TIME, CLASS, SUBJECT, , :- VII, :- SCIENCE
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1) Motion :Motion :- is the change in position of an object with time., There are different types of motions. They are :i) Motion along a straight line (Rectilinear motion), Eg :Motion of a car on a straight road., ii) Periodic motion. Eg :- Motion of a pendulum., iii) Circular motion. Eg :- Motion of the earth around the sun., Periodic motion, Motion along a straight line, , Circular motion
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2) Speed :Speed :- The distance covered by an object in a unit time is, called the speed of the object., Eg :- If a car covers a distance of 100 kilometres in one hour, and a bus covers a distance of 50 kilometres in one hour, then, the speed of the car is more than the speed of the bus., Since the speed of most objects are not constant, the speed is, the average speed., Total distance covered, Speed = -------------------------------Time taken, Uniform motion :- If the speed of an object is constant, it is in, uniform motion., Non uniform motion :- If the speed of an object keeps changing,, it is in non uniform motion.
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3) Measurement of time :Time is measured by using clocks or watches. Clocks and, watches make use of periodic motion., Wall clocks, , Table clock, , Digital clocks, , Watches
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4) Simple pendulum :A simple pendulum has a small metallic bob suspended from a, stand by a thread., If the bob is taken to one side and released, it moves to and fro., The to and fro motion of the simple pendulum is called periodic, motion or oscillatory motion., A simple pendulum, , Thread, , Bob, , A, , O, , B
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Oscillation :When the bob moves from the mean position O to A and to B and back to O,, it is called one oscillation., When the bob moves from one extreme position A to the other extreme, position B and back to A, it is called one oscillation., , Time period :The time taken by the pendulum to complete one oscillation is called its, time period., , Extreme position, , Extreme position, A, , O, Mean position, , B
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Activity :- To measure the time period of a simple, pendulum., Set up a simple pendulum with a thread of length about one meter. Move, the bob to one side and release the bob. Measure the time taken to complete, 20 oscillations using a stop watch or stop clock. Record the observations in, the table. Repeat the activity three times and record the observations. Find, the time taken for one oscillation., The time period is nearly the same in all cases., , Sl.No. Time taken for 20, oscillations, 1, 2, A, , B, O, , 3, , Time, period
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5) Units of time and speed :a) The basic unit of time is second (s)., The larger units of time are minutes (min), hours (h) etc., b) The basic unit of speed is metre per second (m/s)., A larger unit of speed is kilometre per hour (km/h)., , 6) Ancient time measuring devices :Some ancient time measuring devices were Sun dials, Water, clocks and Sand clocks.
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SAND CLOCK, , SUN DIAL, , WATER CLOCK
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7) Measuring speed :The speed of an object can be measured if we know the distance covered, by the object and the time taken., Eg :- If a car covers a distance of 100 kilometres in two hours, then the speed, of the car is :Distance covered – 100 km, Time taken – 2 hr, Distance, 100, Speed = ------------- = ----- = 50 km/h, Time, 2, If we know the speed of the car and the time, we can find the distance, covered by it., Distance = Speed x Time, = 50 x 2 = 100 km, If we know distance covered by the car and the speed, we can find the time, taken., Distance, 100, Time = ------------- = ----- = 2 hr, Speed, 50
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8a) Speedometer :-, , Speedometer is a device which measures the speed of, vehicles in km/h., , b) Odometer :Odometer is a device which measures the distance covered, by a vehicle., Speedometer, , Speedometer and Odometer
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9) Distance – Time graph :Sl.No., , Time, , Distance, , 1, , 0, , 0, , 2, , 1 min, , 1 km, , 3, , 1 min, , 2 km, , 4, , 3 min, , 3 km, , 5, , 4 min, , 4 km, , 6, , 5 min, , 5 km, , If the distance – time, graph is a straight, line, then the object, is moving with constant, speed. If the speed, keeps changing, the, graph can be of any, shape., , Distance (in km), , The distance distance travelled by a car and the time taken is shown in, the table below., , ., ., , 6, 5, , ., , 4, , ., , 3, , 1, , ., , 0, , 1, , 2, , ., , 6 min, 6 km, , 5 min, 5 km, , 4 min, 4 km, , 3 min, 3 km, , 2 min, 2 km, , 1 min, 1 km, , 2, , 3, , 4, 5, 6, Time (in minutes)
