physics

[grumpy]

i have a question about law of gravitation
Q if earth and moon are attracting each other why is not moon collides with the earth?
Q in gravitation each mass exert the same force why arent they cancelled out?

 

[destined007]

Q) first of all, moon is not just attracted by earth, it is also attracted by other planetary bodies like sun, mars, meteoroid, etc.
Secondly, moon is moving around earth by centripetal force. This force makes the moon in rotational orbit.

Q) different masses exert different forces. F=GMm/r^2. F directly proportional to product of masses.

 

[grumpy]

moon s rotational movement is due to gravitation.if there are no other things attracting the moon then what?
and i mean to say suppose you and me are attracting each other and there are no other forces ,we will come close to each other due to our forces which are same .

 

[destined007]

yes that will happen but in case of moon, gravitational force gives rise to centripetal force which keeps the moon in orbit instead of colliding with the earth.

 

[grumpy]

why the forces arent cancelled out.and why centripetal force rises

 

[destined007]

and also that moon is travelling too fast.

1] The relative velocity is large, while the gravitational attraction is small.
The two objects, as they near each other at high speeds, will influence each other gravitationally - they'll deflect their straight paths towards each other. But their v is so high that they pass each other and continue away from each other. (This is a one-time occurence, the two bodies pass and never see each other again. Not a lot of real-world examples for that reason.)

2] The relative velocity is small while the gravitational attraction is large.
The gravity of the two objects overcomes their velocity and they collide. (Any impact is a good example such as Meteorites)

3] The relative velocity is nicely balanced with the gravitational attraction.
The objects come near each other, swing around, and neither collide nor escape. They do a dance aorund each other for a short or even very long time. (Examples include all planets orbiting stars, all moons orbiting planets, etc.)

 

[destined007]

because the moon's velocity is high, the centripetal force with which it rotates around the earth is also big. So moon has the higher tendency to keep its orbit and rotate around the earth.

 

[grumpy]

you mean to say its nicely balanced.
now i am satisfied. thankyou

 

[destined007]

welcome