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(iii) A fireman in a railway engine quickly moves his coal shovel near the furnace and
then suddenly stops it. The shovel comes to rest but the coal continues moving due to
inertia and falls into the furnace

(iv)When a horse running fast suddenly stops, the rider is thrown forward if he is not
firmly seated. This is because the lower part of the rider's body, which is in contact with
the horse, comes to rest while the upper part of his body tends to keep moving due to
inertia

(v)When a moving bus suddenly stops, a person sitting in it falls forward. As the bus
stops, the lower part of his body comes to rest along with the bus while the upper part of
his body continues to remain in motion due to inertia and falls forward.
(iii) Inertia of direction. The inability of a body to change by itself its direction of motion
is called inertia of direction.

Examples
(i)When a bus takes a sharp turn, a person sitting in the bus experiences a force acting
away from the center of the curved path due to his tendency to move in the original
direction. He has to hold on to a support to prevent himself from swaying away in the
turning bus.

(ii) Consider a stone being rotated in a circle at the end of a string. The velocity of the
stone at any instant is along the tangent to the circle. When the string is released, the
centripetal force whirling the stone vanishes. Due to directional inertia, the stone flies off
tangentially.
(iii) When a vehicle moves, the mud sticking to its wheels flies off tangentially. This is
due to inertia of direction. In order that the flying mud does not spoil the clothes of the
passerby, the wheels are provided with mudguards.
(iv) When a dog chases a hare, the hare runs along a zig-zag path. It becomes difficult
for the dog to catch the hare. This is because the dog has more mass and hence has
more inertia of direction than that of hare.

How is the inertia of a body measured?

 Mass as the measure of inertia. Mass of a body is the measure of its inertia.
 If a body has more mass, it has more inertia i.e., it is more difficult to change its
state of rest or of uniform motion.
 For example, if we kick a football, it flies a long way. If we kick a stone of the
same size, it hardly moves. The stone opposes the change in its motion better
than the football because of its more mass. Thus, stone has more inertia than
football.

Newton's first law of motion.