B Hi, I'm learning physics -- Why do things near me not fall toward me?

[Lahouircha]

TL;DR Summary

Why things near me don't fall towards me?

Hi, I'm learning physics because I love it and I have many questions
I'm struggling to understand the difference between laws of motion and universal gravitation

Question 1 :
For example : every object applies a force to another object like the Earth is attracted to the sun, so is the monitor in front of me and other things in this world applying a force towards me, and I'm doing the same thing towards them ?

Question 2 :
In our solar system, all the planets fall towards the sun, but why don't they fall towards each others, I know that the force between the sun and planets is higher than the force between the planets towards each others but those that mean that the lower force in this case the force between the planets to each of the others is "negative", if so is this the reason why the planets in our solar system have this structure and order, and they don't change it?

Sorry for the bad clarification, but I'm trying my hard to explain my struggle.
This may sound stupid, but I really want to learn more, so I would appreciate any help.
Also, if there is anyone want to learn with me from scratch or someone helps with some other questions, contact me.

 

[Nugatory]

every object applies a force to another object like the Earth is attracted to the sun, so is the monitor in front of me and other things in this world applying a force towards me, and I'm doing the same thing towards them ?

Yes. However, before you take this line of thought any further, take a moment - if you skip this step you are only cheating yourself! - to calculate the magnitude of the force between you and the monitor. You might also try googling for “Cavendish torsion balance” to see how physicists have approached this question in the past.

In our solar system, all the planets fall towards the sun, but why don't they fall towards each others,

They do, and the effect shows up as small deviations from the exact elliptical orbits that we calculate when we consider only the effect of the sun’s gravity. In fact, that’s how Neptune was discovered - the orbit of Uranus was showing perturbations that could only be explained by the presence of a previously unknown and more distant planet.

 

[Lahouircha]

Yes. However, before you take this line of thought any further, take a moment - if you skip this step you are only cheating yourself! - to calculate the magnitude of the force between you and the monitor. You might also try googling for “Cavendish torsion balance” to see how physicists have approached this question in the past.
They do, and the effect shows up as small deviations from the exact elliptical orbits that we calculate when we consider only the effect of the sun’s gravity. In fact, that’s how Neptune was discovered - the orbit of Uranus was showing perturbations that could only be explained by the presence of a previously unknown and more distant planet.

Wow, thanks a lot, but you said that we discovered Neptune by the perturbation of the orbit of Uranus but how we know it exact size?

 

[anorlunda]

Wow, thanks a lot, but you said that we discovered Neptune by the perturbation of the orbit of Uranus but how we know it exact size?

Why do you need to know the exact size? You just have to see that the orbit is disturbed by the gravity of another object. Then you start looking for the other object.

 

[Drakkith]

Wow, thanks a lot, but you said that we discovered Neptune by the perturbation of the orbit of Uranus but how we know it exact size?

We didn't. But we had a rough idea of what its mass should be. The difference between Uranus' ideal and actual orbit put constraints on the mass and distance of Neptune. Then, once we find it, we can measure the angular diameter of the planet to determine its size.

 

[Lahouircha]

Why do you need to know the exact size? You just have to see that the orbit is disturbed by the gravity of another object. Then you start looking for the other object.

I don't need it at all, I just googled it up, and it gave me the measure, I'm just wondering how they did it.

 

[berkeman]

I don't need it at all, I just googled it up, and it gave me the measure, I'm just wondering how they did it.

The mass or the radius?

 

[Lahouircha]

We didn't. But we had a rough idea of what its mass should be. The difference between Uranus' ideal and actual orbit put constraints on the mass and distance of Neptune. Then, once we find it, we can measure the angular diameter of the planet to determine its size.

ohhhh thanks now i get it

 

[russ_watters]

I don't need it at all, I just googled it up, and it gave me the measure, I'm just wondering how they did it.

I'm not sure that you're asking a total question here, so two answers:
1. You can measure size with a telescope.
2. You can measure mass by flinging a probe past it and measuring the course deflection (acceleration).

 

[Lahouircha]

The mass or the radius?

the radius

 

[Lahouircha]

I'm not sure that you're asking a total question here, so two answers:
1. You cam measure size with a telescope.
2. You can measure mass by flinging a probe past it and measuring the course deflection (acceleration).

Thanks for the reply, and sorry for the bad structure of the question.

 

[Drakkith]

Note that force isn't everything. The Earth and the Moon both experience virtually the same acceleration under the Sun's gravity, roughly 0.005932 m/s². This is more than twice the 0.002703 m/s² of acceleration the Moon experiences due to Earth's gravity (force on the Moon from the Sun is 4.3x10²⁰ N vs 2x10²⁰ N from the Earth). So one might question why the Moon doesn't fly off towards the Sun. Well, it does. But so does the Earth. Both are accelerating towards the Sun at the same rate.

This is like two skydivers holding on to each other with a single hand while falling. They certainly couldn't hold each other up with one hand if they were stationary on the ground, the Earth's gravity is too strong. But when both are falling at the same rate they can use a single hand to push and pull each other, swing in circles, and many other things.

 

[Lahouircha]

Note that force isn't everything. The Earth and the Moon both experience virtually the same acceleration under the Sun's gravity, roughly 0.005932 m/s². This is more than twice the 0.002703 m/s² of acceleration the Moon experiences due to Earth's gravity (force on the Moon from the Sun is 4.3x10²⁰ N vs 2x10²⁰ N from the Earth). So one might question why the Moon doesn't fly off towards the Sun. Well, it does. But so does the Earth. Both are accelerating towards the Sun at the same rate.

This is like two skydivers holding on to each other with a single hand while falling. They certainly couldn't hold each other up with one hand if they were stationary on the ground, the Earth's gravity is too strong. But when both are falling at the same rate they can use a single hand to push and pull each other, swing in circles, and many other things.

Yes that's true, also I just learned about inertia, so I think it's affect to force a lot.