Motion and Time

Q1. Fill in the blanks.

                           i.        The metallic ball is called the bob of the pendulum.

                          ii.        The symbols of all units are written in singular.

                         iii.        The time taken by the pendulum to complete one oscillation is called its time period.

                         iv.        One microsecond is one millionth of a second.

                          v.        A nanosecond is one billionth of a second.

                         vi.        The distance-time graph for the motion of an object moving with a constant speed is a straight line.

Q2. True/False

                           i.        The basic unit of time is second. True

                          ii.        Every object moves with a constant speed. False

                         iii.        Distances between two cities are measured in kilometres. True

                         iv.        The time period of a given pendulum is not constant. False

                          v.        The speed of a train is expressed in m/h. False

                         vi.        Clocks that measure such small time intervals are used for scientific research. True

Q3. What is the basic unit of time?

Ans. The basic unit of time is a second. Its symbol is s.

Q4. What is the basic unit of speed?

Ans. Basic unit of speed is metre per second (m/s).

Q5. What is speedometer?

Ans. Speedometer is an instrument that indicates the speed of a vehicle.

Q6. What is distance-time graph?

Ans. Distance-time graph represents the speed of an object.

Q7. What is speed?

Ans. The distance moved by an object in a unit time is called its speed.

Q8. What is oscillatory motion?

Ans. The to and fro motion of an object is called oscillatory motion.

Q9. What is motion?

Ans. Motion is a change in position of an object over time.

Q10. What is circular motion?

Ans. Circular motion is rotation of an object along a circular path.

Q11. Give an example of oscillatory motion.

Ans. The to and fro motion of a simple pendulum is an example of a periodic or an oscillatory motion.

Q12. What is non-uniform motion?

Ans. If the speed of an object moving along a straight line keeps changing, its motion is said to be non-uniform.

Q13. What is uniform motion?

Ans. An object moving along a straight line with a constant speed is said to be in uniform motion.

Q14. What is the smallest time interval that can be measured with commonly available clocks and watches?

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

Q15. What is a simple pendulum?

Ans. A simple pendulum consists of a small metallic ball or a piece of stone suspended from a rigid stand by a thread. The metallic ball is called the bob of the pendulum.

Q16. How time was measured when pendulum clocks were not available?

Ans. Many time measuring devices were used in different parts of the world before the pendulum clocks became popular. Sundials, water clocks and sand clocks are some examples of such devices.

Q17. What are quartz clocks?

Ans. Nowadays most clocks or watches have an electric circuit with one or more cells. These clocks are called quartz clocks. The time measured by quartz clocks is much more accurate than that by the clocks available earlier.

Q18. What is average speed?

Ans. Speed or average speed is the total distance covered divided by the total time taken. Thus,