The screw undergoes two kinds of motions, i,e., circular and periodic motions

(i) Length of the scale, that you are using to measure, must be greater than the length of the object.
(ii) The eye must be placed just above the point, that you are reading, otherwise there will be an error due to parallax.
(iii) If the zero mark of the scale is damaged or the edge of the scale is not smooth, then start the measurement from another mark

(a) Land-motorcycle, car.
(b) Water-Boat, steamer.
(c) Air-Aeroplane, helicopter.

Distance is actually defined as length or space between two places. It is clear from the diagram that when we whirl the stone, the space or length between points A and B, i.e. between hand and stone does not change.
Hence, distance is same.

(a) Kanchan is intelligent, helping and has good knowledge of subject.
(b) One correct way for measuring from broken scale is to start from full marks.

We need standard unit of measurements because the unit like handspan, foot, cubit differ from person to person or even indifferent countries. So, for a uniform measurement, standard unit of measurement is really required.

Yes, a person driving a car is in rest with respect to other person in car but in motion with respect to a person standing roadside. State of motion and rest depends upon observer or reference point.

Similarities are given below

(i) The wheels of a bicycle and a ceiling fan execute a rotational motion on a fixed axis.
(ii) The particles of both exhibit circular motion except the particles at the centre.
Differences are given below
(i) Bicycle changes its position while exhibiting circular motion but a ceiling fan does not change its position.
(ii) Bicycle can execute rectilinear motion with translational motion but ceiling fan does not execute rectilinear motion.

Given, distance between Radha's home
and her school = 3250 m
We know that
1 km = 1000m
\(\therefore 1m ={1\over 1000}km\)
Now, the distance between Radha's home and her school in km​​​​​​
\( = 3250 \times {1\over 1000}={3250\over 1000}\)
= 3.25 km

There are mainly three modes of transport which are given below:
(i) Land transports Those transports that run on land are called land transports, e.g. bus and truck.
(ii) Water transports Those transports that run on water are called water transports, e.g. boat and ship.
(iii) Air transports Those transports that run in air are called air transports, e.g. aeroplane and helicopter.

Foot, handspan and arm length are used to measure the length. These are inexact methods of measurement.

1m = 100em = 1000 mm
\(\therefore\)The height of the given person in cm is
= 1.965 x 100 = 196.5 cm
\(\therefore\)The height of the given person in mm is
= 1.965 x 1000 = 1.965 mm.

The two devices that are used to measure length are:
(i) Metre-scale (ii) Screw gauge.

Relative two earth, we are in motion and relative to plane or any other thing in plane, we are at rest

By measuring distance by a particular standard unit of measurement.

(a) The motion of a swing is an example of periodic motion.
(b) 1 m = 100 cm

In ancient times, there were some modes of transportation like bullock cart, horse cart, camel cart, etc.

The device which is used to measure girth of a tree is a measuring tape.

Handspan is a process which is used to measure the length in ancient times.

Rectilinear motion is the motion possessed by the vehicles on a straight road.

Draw a curved line CD. Take a thread and make a knot at one of its ends. Keep the knot made in the thread on point C of the line. Place a small portion of the thread along the line, keeping it tight using your fingers and thumb. Keep on stretching the thread on the curved line till you take the thread to the point D of the line. Make a mark on the thread where it touches the other end of the line at point D. Now, stretch the thread along a metre scale and the length between the knot in the beginning and mark on the thread is measured through scale. This measured length on scale will give you the length of the curved line CD.

The reasons may be as follows
(i) Their scales of measurement may not be standard or they may be using different scales of measurement.
(ii) The length of the scale may not be proper, i.e. the length of scale may be shorter ·than the length they want to measure.
(iii) There may be some errors in the scale which they are using or they may not be using the correct method of observing the scale.

The motions of a wheel of a moving bicycle and a mark on the blade of a moving electric fan are different in the following ways.

While travelling, trees near the track same to be moving back (i.e. opposite to the direction of motion of a train) because there is a relative motion between outside trees and moving train. While in case of co-passengers, the relative motion between we and co-passengers, is zero, so it appears to be stationary.