## Saturday, February 2, 2013

### Are our weights different at day and night?

Discussion point:
Our body's weight is more at day time than at night time because at night both earth and sun attracts towards the same direction while at daytime the sun attracts in opposite direction to that of earth."

It is actually theoretically true that the weight of our body is different at day and night. This necessarily has not to be the weight of our body, which could actually change due to metabolism. An example of any other object would be better, but we will take a person of mass (Mp) 60kg in the example below to find out how much is the difference. Ms and Me are the masses of sun and earth respectively. The distances between the sun and the person are shown in the figure above.

From the figure above, it is clear that
Mday = (Fe - Fs1)/9.81
Mngt = (Fe + Fs2)/9.81

Lets find out the values of Fe, Fs1 and Fs2 using Newtons law of gravitational attraction.
The force of attraction between earth and person,
Fe = 587.85 N

The force of attraction between sun and person at day,
Fs1 = 0.355880505 N

The force of attraction between sun and person at night,
Fs2 = 0.355850612 N

Subsequently,
Mday = 59.88 kg
Mnight = 59.96 kg

The difference in mass at night and day is just 72 grams.
This happens to be the variation of just 0.12%

However if you have a massive object of 100000 kilos, then the difference might be noticeable. The difference in that case would be 12 kilos.