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

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

First of all, take a round pencil and try to wrap the given wire round the pencil making.
25 turns forming a coil. Now, measure the length of the wire that turns formed coil. Divide the total length of the coil by number of turns. This is the thickness of the Wire.

Elastic substances have the property of elasticity, i.e. these can be stretched by applying some force. Therefore, an elastic measuring will not give a accurate measurement. In elastic tape measurement, measurement of same object may be different due to its stretching.

A pace or a footstep cannot be used as a standard unit of length because the length of footstep, forearm length and handspan of different person is different.
Since, standard units must be similar at all places of world and in all kinds of conditions. It should not depend upon body parts and natural phenomenon. So, footsteps and other such measuring systems cannot be use as standard unit.

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.

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

Bullock cart, camel cart etc

We will use the measuring tape to measure chest.

There are\(1\over 1000\) kilometre in 1 metre

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.

(a) Rectilinear motion The handle of bicycle will always move in rectilinear path because it cannot do circular or rotatory motion.
(b) Circular motion The Paddles of bicycle will always move circularly around its chain fixing system because it cannot move in forward direction without the whole chain system.
(c) Both rectilinear and circular The wheels of bicycle will move in rectilinear as well as in circular motion because the wheel as a whole will move forward and its point or particles around the rim will execute circular motion.

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.