class7 time motion chapter 8 science ppt.pptx

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1. TIME AND MOTION CHAPTE R: 9 CLASS: 7 SUBJECT: SCIENCE GRETA GUPTA

2. L earning Objectives 1.Knowledge of Time 2.Understanding of the Simple Pendulum and time period 3.Knowledge of units of time and speed 4.Knowledge of common modern and ancient time-measuring devices 5. Skills of measurement of Speed

3. MEASUREMENT OF TIME IN ANCIENT TIMES The time between one sunrise to the next snrise was called a ‘day’ or ‘solar day’. T he time between one new moon to the new moon was called a ‘month’. T he time taken by earth to complete one revoluion of the sn was called a ‘year’.

4. A ncient clocks

5. D o You Know? The Jantar Mantar is a collection of 19 astronomical instruments built by the Rajput king Sawai Jai Singh II, the founder of Jaipur, Rajasthan. The monument was completed in 1734. It features the  world's largest stone sundial , and is a UNESCO World Heritage site. It is located near City Palace and Hawa Mahal.

6. M easurement of time A ll the clocks & watches use the principle of periodic motion for measuring time. P eriodic motion: A motion that repeat itself at regular intervals of time. O ne of the most common devices to show periodic motion is Simple Pendulum.

7. S imple Pendulum I t consists of a small metal ball( called bob) suspended by a long thread from a rigid support, such that the bob is free to swing back & forth. T he pendulum motion was first studied by Galileo.

8. S OME TERMS RELATED TO SIMPLE PENDULUM L ength of the pendulum: The length of the string (thread) from the point of suspension to the center of the bob. M ean position of the bob: The position of the bob when it is at rest. E xtreme positions of bob: The positions where the bob is at the maximum distance from the mean position, O scillation of the pendulum: One complete to & fro motion of the bob about its mean position. A mplitude of the pendulum: The maximum displacement of the bob from its mean position on either side. T ime period of the pendulum: The time taken by the bob to complete one oscillation. F requency of the pendulum: The number of oscillations made by a pendulum in 1 second.

9. E quation triangle

10. C heck point L abel the following diagram: C lue box: E xtreme position M ean position L ong thread P oint of suspension Amplitude

11. CHECK POINT A simple  pendulum takes 32 seconds to complete 20 oscillations. W hat is the time period of the pendulum? A simple pendulum completes 40 oscillation in a minute .Find its (a) frequency (b) time period . Calculate Time-period of a simple pendulum if it takes 72 seconds to complete 24 oscillations. A simple pendulum takes 15 seconds to complete 5 oscillations. What is the time period of pendulum ?

12. D o you know? Galileo's escapement  is a design for a clock  escapement , invented around 1637 by Italian scientist  Galileo Galilei  (1564 - 1642). It was the earliest design of a  pendulum clock . Since he was by then blind, Galileo described the device to his son, who drew a sketch of it. The son began construction of a prototype, but both he and Galileo died before it was completed.

13. LATEST TREND IN MEASUREMENT OF TIME The principle of simple pendulum is used in pendulum clock. A mechanical wrist watch has a balance wheel which controls the movement of hands. Q uartz clocks & watches measure time accurately. Quartz has a unique property of oscillating when subjected to a small amount of electric current..

14. F or measuring short intervals of time, a stop watch is used. F or the most accurate meausrement, atomic clocks are being used. S topwatch in sports can measure one-tenth of a second Atomic watch A timer is used to record the sequence of an event

15. UNIT OF TIME T he standard unit of measuring time is second(s). Larger units are minutes(min), & hours(h). UNIT CONVESION 60 seconds 1 minute 60 minutes 1 hour 24 hours 1 day 30 days 1 month 12 months 1 year 10 years 1 decade 100 years (10 decades) 1 century 1000 years (10 centuries) 1 millenium

16. OPTICAL LATTICE CLOCK DESIGNED BY Jerome Lodewyck & his team at the Paris Observatory M ost accurate clock, ‘ redefine the second’. U ses laser beams, more than twice as accurate as an atomic clock. I t can be used in telecomunications & satellite navigation clocks

17. MOTION In Science, an object is said to be at rest when it does not change its position with time or with respect to its surroundings. A n object is said to be in motion when its position changes with time or with respect to its surroundings.

18. T YPES OF MOTION

19. SLOW & FAST MOTION An object which takes a longer time to cover a certain distance is said to be slow, whereas an object which takes a shorter time to cover the same distance is said to be fast.

20. S PEED Speed of a moving object is the distance travelled by it in a unit time.

21. CHECK POINT The distance between two stations is 300 km. A train takes 6 hours to cover this distance. Calculate the speed of the train . Sumit covers a distance of 2.4 Km from his house to reach her college on a scooter. If the scooter has a speed of 6m/sec, calculate the time taken by her to reach the college . If a car is moving with a speed of 5Km/h on highway then find the distance travelled by the car in 4 hours?

22. UNITS OF SPEED The standard unit of distance is meter (m) and of the time is second (s) So the standard unit of speed is meter per second (m/s)

23. SPEEDOMETER & ODOMETER S peedometer: An instrument on a vehicle’s dashboard which indicates the speed of the vehicle at that instant of time in kilometer per hur (km/h). O dometer: An instrument which shows the distance travelled by the vehicle in kilometers.

24. N UMERICAL PROBLEMS BASED ON SPEED 1. Find speed when, distance is 142 km and time is 2 hours. 2. Find out the distance covered when, speed is 960 km/hour and time is 1 hour 50 minutes.  3. Determine the time taken when, distance is 7150 km and speed is 780 km/hr. 4. If distance travelled by a train is 495 km in 4 hours 30 minutes, what is its speed? 5. A cyclist covers 950 m in 5 minutes. Find his speed in km/ hour.

25. UNIFORM & NON UNIFORM MOTION An object moving along a straight line path is said to have a uniform motion if its speed remains constant. A n object moving along a straight path is said to have a non-uniform motion when its speed keeps changing. S tudy the picture & find the difference between uniform & non-uniform motion

26. D ISTANCE-TIME GRAPH FOR VARIOUS FORMS OF MOTION

27. DISTANCE TIME GRAPH It shows how the distance travelled by a moving object changes with time.

28. DISTANCE TIME GRAPH The motion of objects showing relationship between distance travelled & time taken to cover that distance can be represented by a graph – Distance time graph. I t shows how the distance travelled by a moving object changes with time.