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# Gravitation and Weightlessness

Welcome to class!

In today’s class, we will be talking about gravitation and weightlessness. Enjoy the class!

### Gravitation and Weightlessness

• #### Gravitation:

It is a type of force that acts on a body across a distance, without any contact between the source and the body. The earth exerts a gravitational force on bodies by which it pulls these bodies towards its Center. That is why when a ball is thrown from a story building; it goes down and not upward. This is why fruits fall to the ground from the tree and do not rise upwards.

In addition, when a stone is thrown upwards it soon stops its upward movement and starts to fall back to the earth. The force of gravity is a universal force. It exists between the earth and bodies and between planets and stars. Gravitational pull determines the weight of objects.

##### Effect of gravitation

The energy of the quanta of electromagnetic radiation is subject to gravitational forces just like a mass of magnitude m = hν/c2. This is so because the relationship of energy E and mass m is E=Mc2.

As a consequence, light travelling toward Earth gains energy and its frequency is shifted toward the blue (shorter wavelengths), whereas light travelling “up” loses energy and its frequency is shifted toward the red (longer wavelengths). The effect of gravitation on light increases with the strength of the gravitational attraction.

Thus, a light beam from a distant star does not travel along a straight line when passing a star like the Sun but is deflected toward it. This deflection can be strong around very heavy cosmic objects, which then distort the light path acting as a gravitational lens.

• #### Weightlessness:

Weightlessness is a condition experienced while in free-fall, in which the effect of gravity is cancelled by the inertial (e.g., centrifugal) force resulting from the orbital flight. The term zero gravity is used to describe such a condition.

Excluding spaceflight, true weightlessness can be experienced only briefly, as in an aeroplane following a ballistic (i.e., parabolic) path.

In our next class, we will be talking about the Earth in Space.  We hope you enjoyed the class.

Should you have any further question, feel free to ask in the comment section below and trust us to respond as soon as possible.

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