CBSE – 7th Standard Science

Chapter 13

Motion and Time 

Q1. What is speed?

Ans. The distance moved by an object in a unit time is called its speed. The most convenient way to find out which of the two or more objects is moving faster is to compare the distances moved by them in a unit time. Thus, if we know the distance covered by two buses in one hour, we can tell which one is slower. We call the distance covered by an object in a unit time as the speed of the object

Q2. What are the types of motion , Explain with examples?

Ans. Straight line circular or periodic oscillary are the types of motion. Running and car moving on a straight road are the example of straight motion, merry-go-round is circular motion and a see-saw, hammer of an electric bell are oscillary motion.

Q3. State the difference between non-uniform and uniform motion.

Ans. In everyday life we seldom find objects moving with a constant speed over long distances or for long durations of time. If the speed of an object moving along a straight line keeps changing, its motion is said to be non-uniform on the other hand, an object moving along a straight line with a constant speed is said to be in uniform motion. In this case, the average speed is the same as the actual speed.

Q4. What is the basic unit and formula to get speed?

Ans. The speed of an object is the distance traveled divided by the time taken to cover that distance, Speed= total distance/ total time Its basic unit is metre per second (m/s).

Q 5.  What events have been used to measure time?

Ans. Periodic events are used for the measurement of time. Periodic motion of a pendulum has been used to make clocks and watches.

Q6. What instruments are used to measure speed?

Ans. A speedometer records the speed directly in km/h. There is also another meter that measures the distance moved by the vehicle, is known as odometer

Q7. Is motion presentable in pictures?

Ans. Yes, Motion of objects can be presented in pictorial form by their distance-time graphs.

Q8. What is the use of Distance-time graphs?

Ans. Distance Time graphs provide a variety of information about the motion when compared to the data presented by a table

Q9. Which is  the common smallest unit of time?

Ans. The smallest time interval that can be measured with commonly available clocks and watches is one second.

 Q10  Is it possible to measure the interval between second?

Ans. Stopwatches and Quartz clocks can measure time intervals as small as one millionth or even one billionth of a second.