NCERT 6th Class (CBSE) Science: Measurements and Motion

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

Answer: Similarities between the motion of a bicycle and a ceiling fan:

1. The blades of a fan and the wheels of a bicycle are fixed at a point.
2. Both have circular motion about their respective fixed points.

Differences between the motion of a bicycle and a ceiling fan:

1.  A bicycle has linear motion, whereas the blades of a ceiling fan do not have linear motion.
2.  The motion of the blades of a fan is periodic, whereas the motion of a bicycle is rectilinear motion.

Question: Why can 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 stretchable. It cannot be used to measure distances because the length of the tape may change on stretching. As a result, the measured length would not be correct.

If you measure the length of an object twice using an elastic tape, then you may get different values of the same length each time. This is because elastic tapes are stretchable.

Question: Give two examples of periodic motion.

Answer: Examples of periodic motion:

1. Motion of a pendulum: The bob of a pendulum repeats itself at a certain time period. This motion is called periodic motion.
2. Motion of a boy sitting on a swing: The motion of a swing repeats itself at a certain time period. Hence, a boy sitting on a swing has periodic motion.

Question: Are senses reliable for accurate measurement?

Answer: Our senses are not reliable for accurate measurement.

Question: Why can hand span and arm length not be used as standard units of length?

Answer: because these vary from person to person.

Question: How many centimetres are there in 1 m?

Answer: 100 cm.

Question: Name the measuring device which can be used for measuring the girth of a tree.

Answer: Measuring tape.

Question: Give one example of linear motion.

Answer: Motion of stone falling from a certain height.

Question: Give an example of circular motion.

Answer: Motion of arms of watch.

Question: Name the types of motion in which a body moves along a straight path

Answer: Rectilinear or linear motion.

Question: State two precautions to be observed while measuring length with the help of a metre scale.

Answer: Two precautions are:

1.  The initial point of distance must coincide with the zero reading of metre scale.
2. The eye should be kept in line with the point of measurement.

Question: Define rest and motion.

Answer: The objects which do not change their positions with time are said to be at rest. The objects which change their positions with time are said to be in motion.

Question: Define the term standard unit.

Answer: The unit that could be used everywhere as a basic unit of measurement is called a standard unit.