2021-22 GRD 7 CH MOTION AND TIME (NOTEBOOK AND WORKBOOK EXERCISE)

 

Diagnostic test-google form

Kwl chart

NEW WORDS

1.    suspended

2.    bob

3.    uniform

4.    periodic

5.    odometer

 

NEW TERMS

Unit: it is a standard segment in which a quantity is measured

Bob: a metallic ball that is hung to one end of a pendulum

Suspended: hung from above

 

Answer the following questions in one word or a sentence.

a.    When do we state that an object is at rest?

ANS. An object is said to be at rest, when it does not change its position with time or with respect to its surrounding

b.    Give atleast two examples of early clocks which are equally effective indoors as well as outdoors.

ANS. Sun dials and Water clocks

c.    What is the working principle of clepsydra?

ANS. To measure the time, it uses the fact that equal amounts of water take the same interval of time to flow through an opening.

d.    On what factor does the time period of a simple pendulum depend upon?

ANS. The time taken by the pendulum to complete one oscillation depends upon the length of the string.

e.    Where are odometers situated in vehicles?

ANS. Odometer which records the distance covered by the vehicle in kilometres

 Answer the following questions in short.

a. What is the difference between speedometer and odometer?

ANS.   Vehicles such as cars, buses, scooters and bikes have speed indicating devices called speedometers.

These devices show the speed of vehicles in km/h.

Inside the speedometer there is an instrument called odometer which records the distance covered by the vehicle in kilometres.

These devices are used to measure speed and distance

 b. What are the two facts on which the motion of an object depends?

ANS. The motion of an object with respect to another object depends upon factors as follows. 1. The distance covered by the object 2. The time taken to cover the distance

c. Define the following quantities:

 i. motion

ANS.  A body or an object is thus said to be in motion when its position changes with respect to time and its surroundings.

ii. speed

ANS. The distance covered by a moving body in unit time is its speed. In other words, the speed of the moving body is the total distance it travels divided by the total time it takes to travel that distance.

d. Distinguish between uniform motion and non-uniform motion.

ANS. A body moving in a straight line covering equal distances in equal intervals of time is said to be moving in uniform motion.

EX. In uniform motion, the distance to time graph shows a straight line.

A body covering equal distances in unequal intervals of time or vice-versa is said to be moving in non-uniform motion

EX. In non-uniform motion, the distance to time graph shows a curved line.

 

Answer the following questions in detail.

a. Compare the terms fast motion and slow motion.

ANS. If we compare the motion of different objects, we will find that all of them do not move or travel with the same speed. We know that a moving body requires a certain amount of time to change its position between any two given points. Suppose your friend takes about 10 minutes to walk and reach school and you take more than 15 minutes to cover the same distance, then we can classify the motions as fast and slow. Here, the motion of your friend is fast, whereas you are slow.

 

b. Describe the working of a candle clock.

ANS. Candle clocks have been used since antiquity.

 For the measurement of time, a candle clock uses a slow burning thin standard candle with many markings.

Each marking indicates the passing of a unit of time as the candle burns throughout the day and night.

A candle clock was an effective way to measure time indoors despite the rain, night, or any other environmental conditions.

 

c. Describe a distance-time graph.

ANS. A distance-time graph is a way of representing the motion of an object in the form of a graph.

The Y- axis of the graph is used to plot the distance, whereas X-axis is used to plot the time.

 This illustrates how far an object moved and how long it took to reach that far.

This is a quick method to analyse the motion of an object.

 The distance-time graph of an object in uniform motion is always a straight line, whereas, the distance-time graph of an object in non-uniform motion is a curved graph.

 

8. Solve the following numerical sums.

a. A train travels at 120 km/hour. In what time will it cover a distance of 1200 km?

 

b. Shree travels a distance of 12 km from her house to school by a bus at 20 km/hr and returns home at 16 km/hr.(SOLVE IT ON YOUR OWN)

 

i. Calculate the time required to reach school from home.

 

ii. Find out the time required to reach home from school.

 

iii. Determine the average distance of the entire journey.

 

 

 Diagram based questions.

a. Observe the diagram and answer the following questions.

 i. Describe oscillation with the help of the above diagram.

ANS. The above figure shows a freely suspended bob.

 When the bob of the pendulum is at B, it is said to be in its mean position.

 When the bob of the pendulum is displaced slightly and released, it begins to move back and forth.

The back and forth motion of a simple pendulum is called oscillation.

ii. Explain at least two ways when the bob shown in the diagram can complete one oscillation.

ANS. When the bob moves from one position and returns to the same position, it is said to complete one oscillation.

 For example, when the bob moves from position B to C then from C to A and then back to B is counted as one oscillation.

Similarly, when the bob moves from position A to C and then comes back to A is also counted as one oscillation.

Thus, the time taken by the pendulum to complete one oscillation is called the time period of that pendulum.

iii. Firstly, the bob of a given pendulum is stroked gently and after that it is stroked with fierce force, will the time periods of the pendulum be the same in both the conditions? Explain.

 

 

HOTS (Higher Order Thinking Skills) SOLVE IT BY YOURSELF

a.    Plot a distance-time graph on a graph paper using the data given in the following table. Also identify the type of the motion.

b.    b. Draw a distance-time graph for the following cases:

c.    i. An object is at rest.

d.    ii. An object is moving upwards with a constant speed

 

 

MIND MAP

 

WORKBOOK EXERCISE