Question

What is weightlessness? Give two examples

Answer 1

Hint : By the term we can understand the complete or near-complete absence of the sensation of weight. No force acts upon the object.

Complete step by step solution:
Let us understand the concept,
The force exerted by the earth on a body is called the weight of the body.
However the mass of the earth can be determined by acceleration due to gravity near the surface of the earth
$g={\displaystyle \frac{GM}{R^2}}$
 $g=9.8m/s^2,R=6400km$, $G=6.67\times {10}^{-11}$
So after we get a general idea of weighing we can easily understand the concept of weightlessness
So how can we actually experience weightlessness? We feel the sensation of weightlessness exists when all contact forces are removed. These sensations are common to the state of free fall.
Freefall is the situation when a body is moving only under the influence of the earth’s gravity.
During free fall, the only force acting on the body is the force of gravity. As gravity is a non-contact force. Contact forces are forces that act between two objects that are physically touching each other
This is the reason why you feel weightless when in a state of free fall.
So where can we actually experience weightlessness?
Example1:
Weightlessness in a satellite –
Consider a body of mass $m$placed on a surface inside a satellite moving round the earth
The forces on the body are gravitational forces and the contact force
So by the Newton’s law
$$\begin{gathered} G{\displaystyle \frac{Mm}{R^2}}-\mu =m\left({\displaystyle \frac{GM}{R^2}}\right) \\ \mu =0 \end{gathered}$$
Thus the surface does not exert any force on the body and hence its apparent weight is zero
Hence, no support is needed to hold a body in the satellite.
Example 2:
Astronauts who are orbiting the Earth often experience sensations of weightlessness
Earth-orbiting astronauts are weightless. They are weightless because there is no external contact force pushing or pulling upon their body. Here gravity is the only force acting upon their body.

Note :
On satellites we feel weightlessness but on moon we do not feel weightlessness though moon is also a satellite because here moon mass is considerable.