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

• B
• Lahouircha
In summary, the conversation discusses the concepts of force, laws of motion, and universal gravitation. It is mentioned that every object applies a force to another object, and this is true for the planets in our solar system as well. The conversation also delves into the discovery of Neptune through the perturbations in the orbit of Uranus and how the planet's mass and size were determined. The speaker expresses their curiosity and eagerness to learn more about physics and welcomes anyone who wants to learn with them.
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.

Lahouircha said:
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.

vanhees71, russ_watters and PeroK
Nugatory said:
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?

Lahouircha said:
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.

vanhees71 and Lahouircha
Lahouircha said:
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.

vanhees71 and Lahouircha
anorlunda said:
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.

Lahouircha said:
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?

russ_watters
Drakkith said:
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

Lahouircha said:
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
berkeman said:
The mass or the radius?

russ_watters said:
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.

russ_watters
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
Drakkith said:
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.

## 1. Why do things fall towards the ground and not towards me?

Things fall towards the ground due to the force of gravity. The Earth has a large mass, which creates a strong gravitational pull. This pull causes objects to accelerate towards the Earth's surface, rather than towards an individual person.

## 2. Why do objects fall at the same rate regardless of their mass?

This is due to the principle of gravity, which states that all objects, regardless of their mass, will experience the same acceleration due to gravity. This means that objects will fall towards the ground at the same rate, regardless of their size or weight.

## 3. Why do objects fall towards the center of the Earth?

This is because the Earth has a spherical shape, and its center is the point at which the force of gravity is strongest. Objects will naturally be pulled towards the center of the Earth due to this strong gravitational force.

## 4. Why do objects feel like they are falling towards me when I jump?

When you jump, you are exerting a force on the ground, causing it to push back on you with an equal and opposite force. This creates the sensation of falling towards you, but in reality, you are just pushing off the ground and experiencing the force of gravity pulling you back down.

## 5. Why do objects fall towards the ground instead of flying off into space?

This is due to the Earth's gravitational pull, which keeps objects on its surface. The Earth's mass creates a strong enough gravitational force to hold objects in place, rather than allowing them to fly off into space.

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