Looking for NEET / JEE Coaching? Enquire Now
• # Need help on answering physics question

Have a physics question? Searching for answers to microtidal forces? On this Ask Expert page you can get the answer your are looking for.

Can you help me in answering one of the Physics question. I want the answer to be explained properly (in detail).
Q. Rank the microtidal forces on your own body, from greatest to least, produced by the following:
a. Moon.
b. Earth.
c. Sun.

Please answer only if you have any idea on the above mentioned question. I want the answer to be answered by the members from Science stream.

• Before understanding tidal force we should be clear in our mind about gravitational force. The gravitational force between two bodies is proportional to their masses and inversely to the square of the distance between them. In Earth-Moon system or Sun-Earth system this is responsible for keeping these bodies tied up to each other while remaining in their orbits. These forces are computed between the centre of these heavenly bodies and act in that direction only.

Now let us consider the gravitational force exerted by moon at different points on earth and acceleration created therein. Because of difference in distances to different parts a differential force is created which is termed as tidal force and is the reason for tides on Earth due to Moon.

In a similar way Sun also creates tides on Earth. Using the general equation F=ma where F is the force and m is the mass and a is the acceleration generated by F, we get a first-degree approximation for tidal force acceleration value = 2GmR/D3
where G is the universal gravitational constant, m is the mass of the heavenly body creating tides on Earth, R is radius of the earth, D is the distance between that body and earth. Please note that D is raised to power 3. The derivation of this equation requires expansion of differential acceleration polynomial in a series and neglecting the higher power terms.

The tidal force by Earth itself on a body placed on its surface is very small as differential acceleration is very very minuscule and is negligible.

Using the approximate formula as above for tidal force of Sun and Moon on Earth respectively we will find that the tidal force of Sun on Earth is quite less (almost half) then that of Moon exerted on Earth.

So the sequence is Moon, Sun and Earth.

Knowledge is power.

• The microtidal forces depend on the relative distance between two bodies and also depends on the side that both the bodies are facing each other. For example, two spherical bodies A and B are facing each other. The force between these two bodies is greater on the sides that face towards each other than the sides that are facing away.

The other factor which affects the force between two bodies is the distance. So the relevant factor is the difference in gravitational force on one side of your body vs the other side along with the average distance from the Sun, Earth and Moon. Since you are closest to earth, the microtidal force on your body is highest on your body by Earth followed by Moon and the Sun.

Thank You
Dr. V. Shashikanth

• Gravitational forces depend on mass and distance. Moon is nearer to earth. Sun is far.
Mass of Sun is 1.98*10^30 kg.
Mass of earth is 5.9*10^24 kg.
Distance between Sun and earth is approximately 150 million kms or 1.5*10^11 meters.

Force acting between earth and Sun is F1= Gm1m2/r^2.

Here G=6.67*10^-11.

M1 and m2 are masses of sun and earth respectively .
r is the distance between Sun and earth.

That gives F1= 3.46*10^22N.

F2 is the force acting between moon and earth.
Mass of moon m2= 7.03*10^22 kg.
Distance between earth and moon is 384000 km or 3.6*10^6m.

F2 is 2.13*10^24 N.

By neglecting all other forces it is evident that moon's forces upon earth will be greater than that of Sun.

The stronger a light shines the darker are the shadows around it.