Question

2. Why does a cricketer gradually pull his hands backwards while taking a catch.
Define inertia of a body? On what factor does inertia depend?
OLOGY​

Answer 1

✪ᴀɴsᴡᴇʀ✪

ɪɴᴇʀᴛɪᴀ

Concept of inertia was first introduced by Galileo. Intertia of a body can be defined as the tendency of the body to continue to be in its original state of rest or uniform motion along a direction. Inertia can be categorised into three types:

1. Inertia of rest.

It is the tendency of a body at rest to continue in its state of rest.

2. Inertia of motion

It is the tendency of a body at a constant velocity to continue in its state of constant velocity.

3. Inertia of direction.

It is the tendency of a body to continue in its original direction of motion.

Newton later incorporated this ideas into his First Law of Motion

ғᴀᴄᴛᴏʀs ᴀғғᴇᴄᴛɪɴɢ ɪɴᴇʀᴛɪᴀ

Inertia of a body depends on

1. Mass of body

Mass of a body is also defined as the measure of its inertia. The term 'inertial mass' originates from this definition of mass.

Heavier bodies are more difficult to move than a lighter body. It is more difficult to stop a moving truck than to stop a cricket ball moving with the same speed. This is because of the fact that body with more mass posses more intertia. When we try to move a big rock, its tendency to be at rest(inertia) is very large and hence more effort is necessary to overcome the inertia. On the other hand, it is very easy to pick up a water bottle because of its small mass and inertia.

2. Velocity

While in newtonian mechanics, velocity has no role to play in deciding inertia of a body , it is not true in case of relativistic mechanics(mechanics of particles at high speed). If a body moves with speed comparable to speed of light(c) , mass of a body increases as the speed increase. It is captured in this famous equation as

$\to m = \frac{m_0} {\sqrt{1-\frac{v^2}{c^2}}}$

where $m_0$ is the rest mass of the body.

So, inertia of a body increases as the particle moves faster. As speed of a particle approaches speed of light(c), it becomes almost impossible to change the state of the particle.

ᴡʜʏ ᴛᴏ ᴄʀɪᴄᴋᴇᴛᴇʀ ɢʀᴀᴅᴜᴀʟʟʏ ᴘᴜʟʟ ʜɪs ʜᴀɴᴅs

When a cricketer catches a ball, he is working against the inertia of the ball. As such, he has to apply a great amount of force. According to Newton's Second Law,

$\to F = ma = m\frac{v-u}{t}$

$\to F \propto \frac{1}{t}$

So, if he catches the ball suddenly, the times taken will be very small and he will need to provide a large amount of force to stop the ball. However if he pull his hands backward while catching the ball, the ball gets more time to comes to rest. As such he will manage to catch the ball with less force and hence less effort. This is the reason behind cricketer's pulling of hands backward while taking a catch.