CLASS 7 MOTION

1. Concept of REST and MOTION
2. Motion and its different forms
Translatory, Circulatory, Oscillatory, Vibratory, Periodic & Non-Periodic, Random, Uniform & Non-Uniform etc
3. Concept of MASS and WEIGHT.
4. Differentiate between MASS and WEIGHT.

1. WELCOME TO MY CLASS Mr. Souvik Chatterjee M.Sc ( Physics)&B.Ed

2. MOTION Motion as a change in position of an object with time Types of motion Translatory Circulatory Oscillatory Repetitive (periodic and non periodic) Random Uniform and Non-uniform motion, Concept of distance and speed(average speed) Weight Concept Differences between mass and weight

3. REST & MOTION A body is said to be at rest if it does not change its position with respect to a fixed point in its surroundings. A body is said to be in motion if it changes its position with respect to a fixed point in its surroundings.

4. EXAMPLE A book lying on the table will not change its position if it is not disturbed and will be considered to be in a state of rest. When a moving car changes its position with respect to a tree or lamp post by the side of the road, the car is said to be in motion

5. REST & MOTION ARE RELATIVE

6. EXPLANATION Suppose we are sitting on a railway platform and looking tree nearby, we say that the tree is at rest because the tree does not change its position with respect to us. But when we see a train passing out of the station, we say that the train is in motion because it is continuously changing its position with respect to us. For a passenger sitting inside a moving bus, the driver of the bus, the driver of the bus is at rest because he does not appear to change his position with respect to the passenger . On the other hand the objects outside the bus such as trees, buildings etc appear to be in motion since they appear to change positions relative to the passenger.

7. KEY POINTS Every body in the universe is in motion. Everyday we see bodies moving around us e.g birds flying, cars and buses are moving, people walking, insects crawling, animals running etc. Our earth also moves around the Sun. We often say that a stone lying on the ground is at rest. But indeed, the stone is also moving along with the E arth around us.

8. An object can be in motion relative to one set of objects while at rest relative to some other set of objects. Thus rest and motion are relative .

9. EXAMPLE Suppose you are sitting in a room. You are at rest in relation to all other stationary objects inside the room. But the room (or home)is on earth and the earth and the earth itself is not at rest. The earth revolves around the sun. It takes one year to complete one revolution around the sun. Thus, you are also revolving with the earth around the sun. Hence in relation to the sun you are in motion

10. DIFFERENT TYPE OF MOTION Different objects have different types of motion. These different types of motion can be classified into the following types. Translatory Motion Rotatory Motion Circulatory Motion Oscillatory Motion Vibratory Motion Periodic Motion, and Non - periodic motion

11. TRANSLATORY MOTION If an object like a vehicle, moves in a line such a way that every point of the object moves through the same distance in the same time, then then the motion of the object is called translatory motion.

12. Translatory motion can be of two types, 1. Rectilinear or linear motion & 2. Curvilinear motion

13. RECTILINEAR MOTION If the motion of the body is along a straight line, it is said to be a rectilinear motion. e.g A ball falling from a height straight towards the surface of earth, a car moving on a straight road and a coin moving over a carrom board etc.

14. CURVIINEAR MOTION If the motion of a body is along a curved path, it is said to be a curvilnear motion e.g - Motion of a cyclist while taking a turn on the road, car moving along a curved path and a ball thrown by an athlete are in curvilinear motion.

15. ROTATORY MOTION A body is said to be in a rotatory motion if it moves about a fixed axis. A rotatory motion is different from a translatory motion because in rotatory motion, the different part of the object move through different distances during the same time. The part of the body near the axis of rotation travels a smaller distance than the distant parts of the body. e.g - The blades of a fan, a spinning wheel or a potter’s wheel, a merry-go-round, rotation of the earth about its own axis etc.

16. CIRCULAR MOTION The motion of a body along a circular path is called circular motion. CIRCULAR motion is a special type of curvilinear motion in which the distance of a moving object from a fixed point (called centre) does not change. e.g - A girl is whirling a stone stone tied at the end of a string in circular path, motion of earth around sun,

17. DIFFERENCE BETWEEN CIRCULAR MOTION & ROTATORY NOTION In rotatory motion, the axis of rotation passes from a point in the body itself whereas in circular motion, the axis of revolution passes through a point outside the body. Thus, the motion of earth around the sun is circular whereas the motion of earth about its own axis is rotational motion. In circular and rotatory motion, the distance of a point of the body from a fixed point always remains the same, whereas it is not the same in curvilinear motion.

18. OSCILLATOTY MOTION The to and fro motion of a body from its rest position (or mean position) is called oscillatory motion. e.g - motion of a pendulum clock, motion of a swing.

19. VIBRATORY MOTION It is also an oscillatory motion with the difference that in vibratory motion, a part of the body always remains fixed and the rest part moves to and fro about its mean position. During the vibratory motion, the shape and size of the body changes. e.g - When we breathe, one chest expands and contracts, When the wire is plucked from the middle, Musical instruments.

20. HOME WORK Define rest and motion. Give example. Explain ‘REST AND MOTION ARE RELATIVE’ Define the following & Give three examples 1.Translational Motion 2. Rectilinear Motion 3. Curvilinear Motion 4. Rotatory Motion 5. Circular Motion 6. Oscillatoty Motion 7. Vibratory Motion Differentiate between circular and rotatory motion. Differentiate between translatory and rotatory motion

21. PERIODIC MOTION A motion which gets repeated after a regular interval of time is called a periodic motion. e.g - ( i )The earth completes one revolution about the sun in nearly 365 days and this motion is repeated after 365 days (ii)The moon revolves around the earth and completes one revolution in nearly 27.3 days and then repeats its motion (iii)A normal person’s heart beats every 0.8 second. (iii)The pendulum of a wall clock repeats its motion after every 2 s

22. NON-PERIODIC MOTION The motion which does not repeat itself after a regular interval of time is called non-periodic motion e.g -A footballer running on a field, application of brakes in a moving vehicle, a ball rolling down the ground gradually slows down and finally stops and motion of tides in the sea.

23. ZIG-ZAG MOTION The motion of particles (called molecules) of a liquid or a gas is random or zig-zag or irregular because they don’t take a specific path and specific direction of motion.

24. MIXED MOTION Sometimes a body can have more than one type of motion simultaneously. Such a motion is called a mixed motion e.g - Wheel of a moving vehicles, A drill used by a carpenter, A carpenter’s saw, A ball rolling on the ground, Rotation of earth

25. WHEEL OF A MOVING VEHICLES Translational + Rotational

26. DRILLING MACHINE Rotatory + Translational Motion

27. CARPENTER’S SHAW Translatoty + Rotatory Motion

28. A BALL ROLLING ON THE GROUND Rotatory + Translational

29. ROTATTION OF EARTH Rotatory + Circular or Curvilinear

30. SPEED Speed is defined by distance travelled by the body in unit time The S.I unit of speed is metre /second(m/s). Other commonly used unit is kilometre /hour(km/h) 18 km/h = 5 m/s

31. UNIFORM MOTION If a moving body travels equal distances in equal interval of time, its motion is said to be uniform. Thus for a uniform motion the speed of the moving body remains constant.

32. EXAMPLE Speed= 2m/s= (4-0)/2 m/s=(8-4)/2 m/s =(12-8)/2 m/s=(16-12)/2 m/s

33. NON-UNIFORM MOTION If a moving body travels unequal distances in equal intervals of time, its motion is said to be non-uniform The speed is variable in different intervals of time.

34. EXAMPLE In the first interval=(5-0)/1=5m/s In the second interval=(15-5)/1=10m/s In the third interval=(30-15)/1=15m/s

35. AVERAGE SPEED The average speed is calculated by finding the ratio of the total distance travelled by the body to the total time time taken in the journey.

36. HOME WORK Define the following and write 3 examples of each of them. Periodic Motion Non-periodic motion Zigzag motion Uniform Motion Non-uniform Motion Define Speed. State its S.I unit. Define Average Speed

37. Define Mixed Motion. Give three example and explain. In the example you must mention the types of motion that the body posseses .

38. NUMERICALS FROM CONCISE PHYSICS 1.A car covers a distance of 160 km between two cities in 4 h. What is the average speed of the car? Average Speed = Distance/Time =160/4 = 40 km/h 2.A train travels a distance of 300 km with an average speed of 60 km/h. How much time does it take to cover the distance? Time = Distance/Speed = 300/60 = 5 h

39. 3.A boy travels with an average speed of 10 m/s for 20 min. How much distance does he travel? Time = 20 min = (20 X 60) =1200 s Distance = Speed X Time = (10 X 1200) m = 12000 m = 12 km 4.A boy walks a distance of 30 m in 1 minute and another 30 m in 1.5 minute. Describe the type of motion of the body and find his average speed in m/s. Non-uniform motion. Total Distance = ( 30 + 30 ) = 60 m Total Time = (1+1.5) = 2.5 minute = (2.5 X 60)s = 150 s Average Speed = 60/150 = 2/5 = 0.4 m/s

40. 5.A cyclist travels a distance of 1 km in the first hour, 0.5 km in the second hour and 0.3 km in third hour. Find the average speed of the cyclist in ( i ) km/h, (ii) m/s Total Distance = (1 + 0.5 + 0.3)h = 1.8 km Total Time = (1+1+1)= 3 h ( i )Average Speed = 1.8/3 = 0.6 km/h (ii) 0.6 km/h = (0.6 X 5)/18 m/s = 1/6 m/s= 0.167 m/s

41. 6. A car travels with speed 30 km/h for 30 minutes and then with speed 40 km/h for one hour. Find: ( i )The total distance travelled by the car (ii)The total time of travel, and (iii)The average speed of car. ( i )First stage - time = 30 minute = 30/60 h = ½ h, Distance = Speed X Time = (30 X ½) = 15 km Second Stage – Distance = Speed X Time = 40 X 1 = 40 km Total Distance = (40+15) = 55 km (ii)Total time = (1+1/2) = 3/2 h =1.5 h (iii)Average Speed = (55)/1.5 = 36.67 km/h

42. MASS Mass of a body is the quantity of matter contained in it. Mass of a body is constant and it does not change with change in position of the body. It is represented by a symbol M S.I unit of mass is kilogram(kg).Smaller unit of mass is gram(g). 1g= 1/1000 kg The mass of a body is measured by a beam balance. The mass of a body is expressed only by its magnitude( i.e numbers and unit ) such as 10.0 kg. Here 10.0 is magnitude and kg is unit.

43. WEIGHT The weight of a body is the force with which earth attracts the body i.e weight of a body is the force of gravity on it. Weight of a body is not constant but it changes place to place. It represented by a symbol W. The S.I unit of weight is newton (N). One newton is nearly the force of attraction of earth on a mass 0.1 kg (or, 100 g). The other unit of weight is kilogram force( kgf ) where 1 kgf = 10 N(More precisely 1kgf = 9.8 N) The weight of a body is measured by spring balance. Weight is expressed by stating its magnitude and direction. Its direction is always Vertically upwards.

44. The relationship between mass and weight is W= mg, Where g=10 N/kg (nearly) (More precisely 9.8 N/kg) Mass and weight are not the same kg is the unit of mass whereas kgf is the unit of weight. For example,a body of mass 10 kg will have weight 10 kgf (or about 100 N)

45. EFFECT OF CHANGE OF PLACE ON MASS & WEIGHT The mass of a body remains constant every where on the surface of earth or any other heavenly body. But the weight of the body changes from place to place because it depends on the force of attraction of earth (or other heavenly body) on the body which differs from place to place

46. EXAMPLE The mass of a body is same on earth’s surface as well as on moon’s surface but the weight of the body on moon’s surface is 1/6 th of the weight of the body on earth’s surface because the force of attraction of moon on that body is 1/6 th of the force of attraction exerted by the earth.

47. DIFFERENCE BETWEEN MASS &WEIGHT (1) It is the quantity of matter contained in a body/ It is the force with which the earth attracts the body. (2)Its S.I unit is kilogram(kg)/ Its S.I unit is newton (N) (3)It is constant for a body and it does not change by changing the place of the body/ It is not constant for a body, but changes from place to place. (4)It is measured by a beam balance/ It is measured by a spring balance.

48. NUMERICALS FROM CONCISE PHYSICS 7.On earth the weight of a body of mass 1.0 kg is 10 N. What will be the weight of a body of mass 37 kg in (a) kgf (b)N? (a) Weight in N=(37 X 10)= 370 N 370 N=370/10=37 kgf (b) 370 N

49. 8.The weight of a body of mass 6.0 kg on moon is 10 N. If a body of mass 30 kg goes from earth to the moon surface, what will be his (a)mass,(b)weight? (a) Mass is constant when the place is changed. So mass remains same as 30 kg. (b) Weight of 30 kg will be = (10 X 30)/6 =(10 X 5)= 50 N

50. HOME WORK Define mass and weight State their S.I unit of mass and weight State the instrument by which mass and weight are measured. Define 1 kgf . How is it related to S.I unit of mass? Differentiate between mass and weight. ( Atleast 4 points)

51. SOME IMPORTANT QUESTIONS Name the type/types of motion performed by each of the following: (a)Vehicle on a straight road (b)Blades of electric fan in motion (c)Pendulum of a wall clock (d)Smoke particles from chimney (e)Hands of a clock (f)Earth around sun (g)A spinning top Ans.(a) Rectilinear/ Translatory / Rotatory (b) Rotatory /Periodic (c)Periodic/Oscillatory (d)Random/Zigzag/Non-periodic (e)Periodic/ Rotatory (f) Translatory /Circular (g) Rotatory / Periodic

52. 2. State the types of motions of the following: (a)A needle of a sewing machine (b)The wheel of a bicycle (c) The drill machine (d) The carpenter’s saw Ans. (a) Periodic/Oscillatory (b) Rectilinear/ Translatory / Curvilinear/ Rotatory (c) Translatory / Rotatory (e) Translatory /Oscillatory

53. NUMERICAL A car travels 1/4 th of the total distance with speed 30 km/h, ½ th of the toatal distance with speed 40 km/ h,last ¼ th of the total distance with 10 km/h. Find the average speed. Ans. Let total Distance be d km First Half , Distance= d/4 km, speed=30 km/h Time= (d/4)/30 = d/120 h Second half, Distance = d/2 km, speed 40 km/h Time= (d/2)/40 = d/80 h Third half, Distance = d/4 km, speed 20 km/h Time = (d/4)/10 = d/40 h Total time = (d/120 + d/80 + d/40)=d(1/120 +1/80+1/40) =d/240(2+3+6)= 11d/240 Average Speed = Total Distance/Total Time = d/(11d/240) = 240/11 = 21.8 km/h.

54. HOME WORK If a train travels from A to B with a speed 20 km/h and returns from B to A with a speed 30 km/h. Find The average speed of the train? If a man walks 1/5 th of his journey with speed 15 km/h, next 3/5 th of his journey with speed 25 km/h and last 1/5 th of journey with a speed 5 km/h. Find the average speed of the man.

55. 1.Let the distance between two stations be d. km From station A to B, Distance travelled =d, Speed= 20km/h Time=Distance/Speed=d/20 h From B to A, Distance travelled-d, Speed=30 km/h Time=d/30 h Average Speed= Total Distance/Total Time = ( d+d )/(d/20+d/30)=2d/d(1/20+1/30) = (2 X 20 X 30)/(30+20)=1200/50 = 24 km/h

56. 2. Let the total distance be d km First half, distance= d/5 km, speed= 15 km/h, Time= Distance/ Time = (d/5)/15 = d/75 h Second half, distance = 3d/5 km, Speed= 25 km/h Time= (3d/5)/25 = 3d/125 h Last half, Distance= d/5 km, Speed= 5 km/h, Time = (d/5)/5=d/25 h Total Time = (d/75 + 3d/125 + d/25) = d(1/75 + 3/125 + 1/25) = d/375(5 + 9 +15) = 29d/375 h Average Speed = Total distance / Total Time = d/(23d/375) = 375/29 = 12.93 km/h

57. THANK YOU