/sci/ - Science & Math

[Anonymous No.2788558]

Right, can someone explain this to me, I'm sure it's real simple but I'm a bit retarded when it comes to shit like this and want a proper answer.

So gravity is a force which pulls things together right, thats why when we jump we come back to the earth because it has so much mass and that attracts us. My question is why doesn't the moon fall into the earth instead of orbiting it, and to a greater degree why doesn't the erath fall into the sun. I mean why doesn't gravity attract them.

I did a bit of googling and the best answer I found told me it was falling into the earth, but because of it's speed it was falling AROUND the earth, which kinda made sense but didn't really.

Can anyone answer this simply for me, it's pretty confusing.

[Anonymous No.2788566]

because of centrifugal force and inertia

[Anonymous No.2788572]

> moon fall into the earth instead of orbiting it,
The moon is falling towards the earth. It's just moving so fast it keeps on missing time after time

[Anonymous No.2788573]

>>2788566

But why doesn't it eventually fall to the earth, why does it stay in place in the same orbit?

[Anonymous No.2788576]

because of other planets and stars

[Anonymous No.2788579]

>>2788572

THAT MAKES NO SENSE

[Anonymous No.2788585]

The Earth bends spacetime. The moon is moving in a straight line in curved space.

http://4.bp.blogspot.com/_vJuy7rnHTyQ/TMsyNVO7qYI/AAAAAAAAAGg/l_DZwTqapX8/s1600/Spacetime_curvature..
gif

That .gig sort of shows how this works.

[Anonymous No.2788587]

>>2788573
The only reason it would slow down enough to fall into the earth is if something interacts with it. Remember, the moon is not encountering resistance from the Earth's atmosphere.
Remember your Newtonian Physics: an object in motion will remain that way unless acted upon by an outside force

[Anonymous No.2788588]

Gravity is not a force. It is merely the fabric of space and time bending due to the immense masses of objects. When something falls towards on object, there is no force, it is just falling through the fabric of space time.

[Anonymous No.2788590]

Look at a small segment of the orbit. You can see that it is falling.

Note that falling means that the vertical component of its velocity is changing, not that it's getting closer to the earth.

[Anonymous No.2788593]

>>2788588
>>2788588
Gravity is a force. It is one of the 4 fundamental forces of nature

[Anonymous No.2788599]

>>2788587
Eventually the moon would lose energy and it's orbit would becoming smaller until it collided with Earth.

Why use Newtonian physics to explain gravity when it is common knowledge that Newton's theory of gravity isn't right?

[Anonymous No.2788602]

>>2788588
>claims gravity is not real
>asserts that the "fabric or space/time" is real an not a metaphor

[Anonymous No.2788608]

>>2788599
Newtonian Physics=/=Newton's theory of gravity

get your theorems strait, bud

[Anonymous No.2788605]

>>2788585

Thanks, that';s helpful and all, but still if that's how it's meant to be, it would surely fall into the earth because the earth is lower in the....i dunno....space time anaolgy or whatever. But I kind asee what you're saying.

[Anonymous No.2788613]

>>2788590
>Note that falling means that the vertical component of its velocity is changing, not that it's getting closer to the earth.

I realized that this could be read in two different ways, only one of which is correct for a circular orbit.

At any time, if you find the direction that's vertical (away from earth) and hold that direction fixed, you'll see that the component of the moon's velocity in that direction is changing.

But if you don't hold the direction fixed, then the vertical component of velocity stays constant for a circular orbit (for a real orbit, it will oscillate a bit).

[Anonymous No.2788623]

>>2788572
Basically this.
Same with sun-earth and all other gravity relations.

Astronauts that orbit earth are not weightless they are freefalling.

[Anonymous No.2788625]

>>2788599
Wrong. If anything the Moon will gain energy and escape the Earth's gravity as the Sun and tidal forces are constantly imparting energy to it.

[Anonymous No.2788631]

if yer so smuht than how didt he moon get their?

[Anonymous No.2788634]

Gravity is a loose term.

Newtonian gravity, i.e mass affecting mass, has been dropped by modern physics. We tend to think of bends on the space time, due to the fact that light is affected by gravity; Black holes exist, yet you cannot see them.

General relativity is the current theory, ie, object followw the direction of the medium that is space time.
-S

[Anonymous No.2788635]

>>2788590
>>2788613
On further thought that last sentence is pretty misleading. Velocity vs. position has nothing to do with it. I'll repost without it.

[Anonymous No.2788637]

>>2788635
Look at a small segment of the orbit. You can see that it is falling.

[Anonymous No.2788639]

>>2788585
This is wrong. Lightrays move in "straight lines" or geodesics through the curved spacetime, and since light doesn't orbit the sun, earth doesn't move on such a straight line. However, earth is "big enough" to be influenced by the tidal forces that originates from the spreading of geodesics which takes place since the sun deforms spacetime slightly, and these tidal forces keep earth in orbit around the sun.

[Anonymous No.2788653]

Anyone bringing up spacetime curvature in this thread is missing the point. If the OP doesn't understand why the moon doesn't fall to the earth in the Newtonian model, he's not going to understand it in general relativity. And neither one is exactly right; both are just models that describe the real world to a very good approximation under certain circumstances.

[Anonymous No.2788657]

How gravity works:
<div class="math">R_{ab} - \frac 1 2 R g_{ab} = 8\pi T_{ab}</div>
(using abstract index notation, no dirty coordinates here)

[Anonymous No.2788687]

OP here.

Imagine I'm a fucking 7 year old or something. Describe it it simple words.

Jesus what's wrong with you guys.

Also, thank you for you who hjave tried to give me decent answers, I just need it simpler.

[Anonymous No.2788712]

Force = mass * acceleration.

Acceleration is a change in the velocity. Velocity is a vector, which means it has a magnitude (how large it is) and a direction. So acceleration can mean that the speed of an object changes, or that its direction changes.

When the force is perpendicular to the velocity, the only thing that changes is the direction of the velocity.

If there were no gravity, the moon would fly away from the earth on a straight-line path. The earth's gravity changes the moon's velocity, making the moon's trajectory curve into an approximate circle around the earth.

[Anonymous No.2788714]

>>2788687
It's falling constanty.
It's also moving constantly.

>>2788637
See that pick?
There moon is currently moving in the direction of the arrow(straight). But because it keep falling it curves down.

It's falling towards the earth and moving away at the same time and those speeds are balanced.
Because if this it doesn't move away or come closer instead it only orbits around us.

Imagine a cannon that shoots a ball very fast. The ball keeps falling and hits the ground. If the ball goes fast
enough then it start flying as earth curves downwards at the same speed it falls towards the earth.

[Anonymous No.2788720]

It moves too fast, it works the same way as satellites.

[sme No.2788722]

http://www.lightandmatter.com/html_books/1np/ch09/ch09.html

[Anonymous No.2788723]

Okay to put it simply - basically what I remember from GCSE Physics - the moon is moving fast going sideways, so to speak, however at the same time the Earth's gravity is pulling it downwards. The combination of the "sideways" and "downwards" movement cause the moon to move in a circular orbit around the Earth.

[Anonymous No.2788736]

Also this:
Experiment with it using different speeds and distances and see for your self

http://dan-ball.jp/en/javagame/planet/

You see that if you give too little speed to the planet it crashes.

[Anonymous No.2788739]

[Anonymous No.2788743]

[Anonymous No.2788748]

>>2788714

OP here, that cannon thing works. Seriously, this is the first time in four years I've actually appreciated what someone has to say on 4chan. Thanks. I kinda get it now.

One more question: How did it start moving so fast, I mean, when the moon was formed, and when the earth was formed, when they wern't going so fast, why did they not fall into the earth then?

[Anonymous No.2788768]

>>2788748
I may be wrong in this (/sci/ please correct me if I am) but I think that most stars and planets are formed from supernovae and so because of that they are already very fast moving.

[Anonymous No.2788778]

>>2788748
As far as the moon, the current theory is that there was a Mars-sized body that hit the earth, causing debris to be ejected, part of which formed the moon. So it was always fast-moving.

[Anonymous No.2788798]

>>2788778

Shit really? That's fucking awesome. I love science.

[Anonymous No.2788803]

its like when water gets sucked down the drain in a bathtube. the water doesnt all go directly into the hole it swirls around for a bit. THe force pulling the water towards the drain is so strong that the water actually goes past the drain and then is caught be the suction again creating a swirling motion

[Anonymous No.2788805]

>>2788748
At the birth of our solar system there was this disk of gas
This disk was spinning around its center of mass.
It started to condense and at the center sun was formed
smaller lumps of matter formed form the material that was left behind, these we call planets.

In the beginning there were more planets than today.
Some of the planets that formed had unstable orbits and they eventually collided.

Eath was formed from several of these smaller planets.
The last collision flung matter from earth to space.
Most of it come back to earth but some of it formed the moon. This material had enough velocity to stay in the orbit.

So our planets movement is caused by the spinning gas disk. Moon got its movement from the colision energy.

[Anonymous No.2788815]

>>2788637

Im scared now. What if the moon actually reaches the earth and crashes in?

[Anonymous No.2788817]

>>2788815
It is moving away so no reason to worry.

[Anonymous No.2788821]

Imagine if you shoot a canon ball parallel to the surface of earth from the top of a mountain. It will fall to the earth but if it goes fast enough it will orbit the earth.

[Anonymous No.2788846]

I can't believe nobody on /sci/ answered this correctly yet.

Newton's First law: Every body (in this case- moon) remains in a state of constant velocity and in a straight line unless acted upon by an external force (in this case, Earth).

Moon wants to go in a straight line, Earth keeps it in orbit with gravity. If it were to come closer to earth, Earth's gravity must be stronger, but even if it was, the moon would only be closer- it wouldn't ever actually hit.
Spin with your arms out, then pull your arms in as you spin. This should give you a good idea why it works the way it does.

[Anonymous No.2788932]

I've always found this kind of image helps greatly in visualizing what's going on.

[Anonymous No.2788970]

>>2788932

That's a really good example, well played.

[Anonymous No.2789436]

>>2788815
The moon is actually moving away from the earth at a rate of like 2 cm per year or something...

there would still be terrible consequences if we 'lost' the moon... mainly the eventually total fucking of the seasons.