# Motion and Measurement

## NCERT Solution

#### Fill in the blanks:

- One metre is ______________ cm.
**Answer:**100 - Five kilometre is ______________ m.
**Answer:**5000 - Motion of a child on a swing is ______________.
**Answer:**Periodic motion - Motion of the needle of a sewing machine is ______________.
**Answer:**Periodic motion - Motion of wheel of a bicycle is______________.
**Answer:**Circular motion

## Answer the following questions

Question 1: Give two examples each, of modes of transport used on land, water and air.

**Answer:** Land: Bus, Water: Ship and Air: Airplane

Question 2: Why can a pace or a footstep not be used as a standard unit of length?

**Answer:** Length of footstep can be different for different persons. Using it as a standard unit of length would create confusion. Hence, a pace or a footstep cannot be used as a standard unit of length.

Question 3: Arrange the following lengths in their increasing magnitude: 1 metre, 1 centimetre, 1 kilometre,1 millimetre.

**Answer:** 1 millimeter < 1 centimeter < 1 meter < 1 kilometer

The height of a person is 1.65 m. Express it into cm and mm.

**Answer:** We know that 1 m = 100 cm

Hence, 1.65 m = 1.65 × 100 = 165 cm

Now, 1 cm = 10 mm

Hence, 165 cm = 165 × 10 = 1650 mm

## Answer the following questions

Question 4: The distance between Radha's home and her school is 3250 m. Express this distance into km.

**Answer:** We know that 1000 m = 1 km

Hence, 1 m = 1 ÷ 1000 m

Hence, 3250 m = (1 ÷ 1000 m) × 3250 = 3.25 km

Question 5: While measuring the length of a knitting needle, the reading of the scale at one end is 3.0 cm and at the other end is 33.1 cm. What is the length of the needle?

**Answer:** Here; reading at the beginning point = 3.0 cm

Reading at the end point = 33.1 cm

Measurement = Final reading – Initial reading

= 33.1 – 3.0 = 30.1 cm

Question 6: Write the similarities and differences between the motion of a bicycle and a ceiling fan that has been switched on.

**Answer:** : Similarities: The wheels of the bicycle and the ceiling fan are in circular motion.

Difference: While the bicycle also shows translatory motion, the ceiling fan remains fixed at a place.

Question 7: Why could you not use an elastic measuring tape to measure distance? What would be some of the problems you would meet in telling someone about a distance you measured with an elastic tape?

**Answer:** An elastic measuring tape is highly flexible and hence it would give different readings at different times. Hence, an elastic measuring tape cannot be used to measure distance.

Question 8: Give two examples of periodic motion.

**Answer:** Two examples of periodic motion are; motion of the pendulum of a clock and motion of a swing.