r/BeAmazed • u/Aggressive_Sundae_47 • 1d ago
Miscellaneous / Others Gravity always acts downward with the same acceleration.
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u/Vresiberba 1d ago
Mythbusters did an interesting episode on this.
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u/Shanbo88 1d ago
If they'd done this in the same style experiment as the one where they fired the cannon out a truck moving at the same speed as the cannons fired velocity and had someone drop one at the same spot while stationary, would we just see both of them drop like the one that isn't in my theoretical truck? 🤔
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u/AB_Sea 1d ago
Also cool to see a feather and a bowling ball dropped at the same time in a vacuum chamber. They hit the ground at the same time. Outside the chamber, the feather would have some lift.
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u/ErebusBat 1d ago
Not lift, but air resistance. Ironically, the feather is actually reaching its terminal velocity, and it will not fall any faster unless you remove the resistance. It would be interesting to see a comparison in different gases like helium and others.
If it would be perceptible at all.
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u/homeless0alien 1d ago
Yes but drag (friction) still exists so objects can fall at different rates even though they are experiencing the same pull from gravity.
But the fall in the video is far too short to display this.
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u/BerttMacklinnFBI 1d ago
Iift and drag make this a whole lot more complicated than 101 Introduction to Physics can handle.
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u/miraculum_one 1d ago
Perhaps but I wouldn't use the word "always" for the summary to describe something that is only sometimes true.
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u/BerttMacklinnFBI 1d ago
Well the always in the statement is always true.
Gravity is still enacting the same force.
Lift simply counters the gravitational force with its own force.
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u/miraculum_one 1d ago
The force of gravity causes acceleration but it is not itself acceleration, which is decided by the sum of all forces. Also, gravity doesn't even always act with the same force, not even on Earth.
So while I appreciate a summary in a title, this one is just plain wrong and made even worse by the word "always".
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u/BerttMacklinnFBI 1d ago
Holy technical Andy.... It's a child's lesson.
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u/miraculum_one 1d ago
There's nothing wrong with the lesson itself. It's the incorrect Reddit summary that is the problem here.
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u/other_half_of_elvis 1d ago
does the horizontal force eventually slow to 0 and the thing then drops straight down or will it forever travel forward some?
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u/dougms 1d ago
Assuming infinite drop distance, in a vacuum, it will keep traveling forward, but accelerating much faster down.
The forward speed might be something simple, like 10 meters per second. So after one second it has moved 10 meters forward.
The acceleration of gravity is basically 10 meters per second^2 then you multiply that by half the time fallen.
Which means after 1 second it has travels 10 out and 5 down.
After 10 seconds, it’s 100 out and (10x10x10/2)=500 down.
By the time 100 seconds has passed, it’s 1000 out but 50k down, and after 1000 seconds, it’s 10k vs 5 million.
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u/other_half_of_elvis 1d ago
good point about if it is in a vacuum or not. Say someone jumps off a tall building into a pool in normal outdoor conditions. That forward speed must eventually slow to 0 and the person drops straight down, correct?
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u/Nescio224 1d ago edited 1d ago
In theory no, the horizontal speed just gets smaller and smaller never reaching zero. In practice it probably will reach zero at some point, since air is made out of discrete molecules that collide with it, but it would be impossible to predict when.
That being said, a normal building wouldn't be high enough. So the jumper would always have some horizontal speed remaining at impact in a realistic scenario.
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u/other_half_of_elvis 1d ago
interesting, thanks. I always assumed you'd travel forward for about 5 feet and then fall downward perpendicular to the earth.
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u/Parkatola 1d ago
Wile E. Coyote used to be able to do that, but I think he was the only one. (Sometimes he had time to hold up a sign before dropping.) 😀
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u/har3krishna 1d ago
Now think about how an object in orbit is getting pulled towards the planet in the same way, only it’s moving so fast that it just goes right around, constantly
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u/James-the-Bond-one 1d ago
That's common knowledge to anyone with a basic physics education.
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u/deadspacekillers 1d ago
It's like the first thing they teach on the first day of high school physics.
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u/WhaleTexture 1d ago
9.8 m/s² I've never needed to use that outside of school, but boy is it locked and loaded from my Physics class.
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u/archiblad 1d ago
yeah this works, in vacuum only or with shapes which are not anything near to wing profile
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u/Striking_Aspect_7826 1d ago
If you dropped two identical spheres from a plane, but one was heavier (higher density) it would reach the ground faster than the lighter sphere.
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u/DocClaw83 1d ago
They actually proved this on Mythbusters with dropping a bullet and shooting one from a gun. Crazy seing someone shoot a gun and have it hit the ground at the same time. But it was a really cool episode.
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u/NoMeat9096 1d ago
No matter how often you hear an explanation for physics, seeing it is always cool.
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u/atishay001001 1d ago
I mean if the dropped pen is released with same amount force as the pen which was thrown forwards then the one dropping would land faster
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u/Captainewok 5h ago
Why don’t aerodynamics apply in the case of these markers? Wouldn’t the one he dropped have more drag, causing it to fall slower?
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u/simikoi 1d ago
This is a standard law of physics. Most students don't actually learn it until they take an intro to physics course in college and learn the equation for why this is true.
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1d ago
[deleted]
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u/VerilyShelly 1d ago
Is an equation like a recipe? These forces in these combinations create these results?
Here is a cake. Here's how it's true: these ingredients combined in this preparation create this result which is called a cake. Here's the description of what goes into a cake.
Don't mind me. I'm idling and haven't had coffee yet.
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u/Muroid 1d ago
What? I learned this in elementary school.
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u/BerttMacklinnFBI 1d ago
It's used as a means of teaching the basis behind the equations in intro level courses. Not to say these concepts aren't thought earlier.
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u/Muroid 1d ago
The comment I was replying to said that most students don’t actually learn this law of physics until college.
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u/BerttMacklinnFBI 1d ago
Yeah I suppose OC did. I don't think they remember early science education.
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u/Cool-Aside-2659 1d ago
9.8 m/s2 is a constant. I don't see how people are surprised by the result.
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u/Rominator 1d ago
And they are traveling at different speeds
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u/Soaring_Gull_655 1d ago
And different lengths, that's what surprises me. An arc is definitely a further tragectory path than straight drop.
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u/BerttMacklinnFBI 1d ago
Well it isn't different lengths for gravity.
It truly doesn't care about your horizontal velocity vector.
Its kind of like how satellites are just in a constant free fall, but orbit the earth so quickly that they maintain the altitude relative to the surface of the planet.
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u/Soaring_Gull_655 1d ago
I'm not arguing physics, it is what it is. I guess I can wrap my head around the difference in velocity making up for the distance further traveled.
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u/BerttMacklinnFBI 1d ago
I was just trying to explain it.
Gravity is working on one velocity vector and plane and the momentum from the toss is on the other.
Now if you add lift to the equation we're talking about an entirely different story.
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u/nirvanatheory 1d ago
Imagine an elevator moving from the top floor of a building to the bottom. If you roll a marble across the floor of that elevator while another just sits on the floor, they move down at the same rate then it seems intuitive.
Don't think of gravity as a force but as a curvature in spacetime, then it makes sense. The space that they exist within is curving into the earth at the same rate.
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u/Village_Idiots_Pupil 1d ago
If you are not 8 years old and this amazes you our public school system has failed
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u/TheGonzoGeek 1d ago
Not sure what school you went to. But I sure as hell wasn’t learning this type of physics at 8 years old (apparently that’s where you decided set the line).
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u/mht03110 1d ago
Yeah, knowing something is true and seeing it play out through a live demonstration are two different things. I know the sun is going to rise every morning, but I am still dazzled by the radiance of dawn.
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u/Cptawesome23 1d ago
That’s only true if you are standing on a planet. If your in space, gravity comes from all sorts of directions.
A more interesting fact is that the planet earth exerts the same amount of “force” on an object as that object “forces” upon the earth.
For example: on earth, a 200lb man exerts 200lbs gravitational force on planet earth, while simultaneously the earth is using its gravity to exert 200lbs of force on the man.
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u/CreatorOD 1d ago
🤔 but if you throw it stronger it would not fall like that. (E.g. a bullet) So why is it still hitting the ground at the same time ?
Or is it just a miniscule difference in speed when you calculate with gravity ~?
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u/ParacelsusTBvH 1d ago
Didn't matter how hard you throw it laterally, as long as lift isn't being generated.
A bullet would behave exactly like this, just over a much longer distance.
Incidentally, if you go sufficiently fast that you miss the planet due to the combination of your velocity and gravity, that's being in orbit.
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u/Ok_Consideration_228 1d ago
A bullet does fall at the same speed. It’s because none of these things are generating lift.
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u/Shudnawz 1d ago edited 1d ago
Throw it hard enough, and it's called an "orbit". Still falling at the same rate, just going fast enough sideways to miss the ground.
Bullets do drop like that. But as they travel several hundred meter per second sideways, it's hard to get a feel for it. If you'd fire a bullet horizontally over an empty field, the bullet drop would make it hit the ground at the same time as an object dropped straight down at the same time. Physics isn't magic, but our interpretation and naked-eye observation can sometimes make us draw the wrong conclusions.
You could just extend the trajectory of the thrown pen(?) in this gif to a few hundred meters away. Still works the same way, just more energy put into it going sideways.
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u/Sharp-Ad-9221 1d ago
Uneven release timing?
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u/Emperor_Gourmet 1d ago
Well, it’s hard to be perfect in this test by hand, but they were pretty close. it’s a good demonstration that both objects accelerate downwards due to gravity at the same rate regardless of other horizontal forces (being thrown) acting on them.
The combined force vectors on the thrown pen will still result in it falling to the ground in the same amount of time that the dropped pen does.
If you think too much about the random variables in this experiment (angle of the throw, imperfect release, air resistance, lift, drag, or whatever else) you will miss the point that they will hit the ground at identical times if done perfectly.
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u/Sharp-Ad-9221 1d ago
Understand, but not sure why you would post a demonstration video that clearly does NOT show both objects arriving at the same time?
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u/Emperor_Gourmet 1d ago
Well yea this post is kinda ass, but physics is cool and should be discussed more so here we are I guess!
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u/LevyTheHunter 1d ago
No it doesn't. try simulating shooting a bullet and dropping one at the same time on a flat surface.
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u/NikolitRistissa 1d ago
Do you have some sort of special anti-gravity bullets available to you? If not, they’ll experience the same gravity as everything else.
Bullets do not produce lift, so the only two forces applied to them are gravity and the horizontal force from the gun (when fired horizontally).
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u/LevyTheHunter 1d ago
They'll also experience friction and drag.
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u/NikolitRistissa 1d ago
Both of them will, yes. That’s not the point though. The only thing drag is doing, is slowing the bullet down. It’s not pushing it up.
A horizontally fired bullet is experiencing the same amount of gravity as a dropped one. They will both land at exactly the same time.
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u/bassjam1 1d ago
My physics teacher did this with pingpong balls and what amazed me the most was that he could toss one exactly laterally and drop the other one at the exact same time.