# Tagged Questions

The Newtonian model of gravity in which the force between two objects is given by GMm/r^2.

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### Will a bullet dropped and a bullet fired from a gun horizontally REALLY hit the ground at the same time when air drag is taken into account?

In a world without air, I understand they definitely would. However, with drag taken into account, I think they wouldn't. Since the drag force varies proportional to the square of speed (ignoring the ...
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### How much pressure does the earth's central atom experience?

If mass is distributed evenly about it: "central atom", then it should be weightless right? If reasonably so, does it still experience the pressure? I would like to calculate, but I'm not so ...
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### Does juggling faster less work then juggling slower?

I got this idea when juggling. Let's say three balls with the standard technique. When I throw the balls higher it is harder (more work), but since it takes more time for them to fall back I work less ...
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### My total potential energy?

The potential energy in a uniformed gravitational field is $mg \cdot \Delta h$. This assumes of course that $g$ doesn't change and only gives the difference in potential energy for $\Delta h$. How ...
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### What is the intuition behind “Net Work is Zero”?

I tried searching the answer to this all over the internet, but still cannot grasp this concept. So, when a book is being lifted, let's say $25 meters$ with a mass of $4kg$, with constant speed. I ...
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### Can very large objects have a gravitational moment?

I was reading this answer about center of gravity vs. center of mass and it stated: Consider the Sears Tower. Its CG is about 1 millimeter below its CM. The reason why is because the base of the ...
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### Why does the water rise upwards when the bottle fall down with accleretion $>>g$?

When a medium-sized bottle filled with water quarterly falls from a height with acceleration $g$, the water remains calm. But when it falls with acceleration $>>g$, the water abruptly rises up ...
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### What's the difference between centre of mass & centre of gravity for massive bodies?

My book says: For most of the small objects, both are same. But for mammoth ones, they are really different ones. And in a gravity-less environment, COG is absent; COM still exists. Ok, what's ...
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### How to find gravitational acceleration given $k$ in a power function

I have a problem that has been bugging me for a week, and I can't figure it out. We know the power function: $$y=kx^n$$ I also have a set of data: I took the natural log of both of these data ...
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### Pendulum's motion

Consider a pendulum in it's balance point hanging from ceiling. It can swing in all the directions in the space. The pendulum can only swing in a sphere(the string can't bend). Now, is it possible to ...
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### What Is the Physics principle behind dropping a stone into a cup of water?

I have been doing an experiment about relationship between drop height of a stone and the loss of water in the cup it lands in. I found that after dropping the same stone into a cup with the same mass/...
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### Relation of gravitational pull with no air friction [duplicate]

I am confused between the gravitational pull and the air friction on the moon. Let me give you an example, I have learned that the greater the mass of the body the more gravitational force it ...
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### From escape velocity to gravitational acceleration

If all you are given is the escape velocity from the surface of Earth can you back calculate to Earths 9.8 m/s^2 gravitational acceleration? In the end what I am looking for is a formula with Escape ...
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### How Earth's Gravity is more powerful than its centrifugal force?

How Earth's Gravity more powerful than centrifugal force? The earth spins all the time but we are not holding onto something to avoid drifting off in space cause of the centrifugal force.
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### Why would we weigh less at earth's center?

why we would weigh less at earth's center(as opposed to sea level). Looking around the net, I have seen different approaches to this problem, each with different solutions. According to Newton's ...
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### A falling object's position [duplicate]

I have asked this previously, with a very useful answer but I was not able to solve my problem. I'll try to make it more simple, basically: Find the radius, $r$ of an object after a time, $t$ if ...
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### Calculating the velocity of an elliptical orbit

I need an explanation as to why my solution to this problem doesn't work (please do not give me an answer or tell me exactly how to do it as this is a homework question that I need to do myself, hints ...
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### How to expand this equation considering acceleration due to gravity into 3D vector space?

How can we expand this following equation into 3D vector space? I learned this equation from this answer: Don't heavier objects actually fall faster because they exert their own gravity? The ...
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### Is there a peak gravitational force between bodies?

Suppose Object A is exerting gravitational force on Object B. Object A increases in mass, and so increases in volume, increasing the gravitational force on Object B. But, since mass occupies space the ...
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### Gravitational field intensity inside a hollow sphere

It is quite easy to derive the gravitational field intensity at a point within a hollow sphere. However, the result is quite surprising. The field intensity at any point within a hollow sphere is zero....
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### Can you stop an electron in vacuum?

If we shoot an electron in vacuum tube, then stop it with electromagnetic field, and switch off the field, what will happen with electron? Will it continue its movement? If there is a gravitational ...
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### A Special Case About Projectile Motion [closed]

There is a common fact about projectile motion. Let me remind you with an example: Assume that you are aiming at a hanging banana on a tree. If there were no gravitational force, the bullet would ...
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### Gravitational law [closed]

Newtons gravitational law is $$\ F = \frac{G m M} { r^2 }$$ But I have seen in some cases where they take an angle like $\cos\theta$ Find the force of attraction between the masses $m$ and $M$
Anyone can give me some clues on how this can be proved? What kind of drag force is used? A particle is projected vertically upward with an initial speed $v_0$ near the Earth's surface. Show that ...
I am trying to find the gravitational potential energy of a 1kg geostationary satellite above the earth. So far: $E=mgh$, and $g=GM/r^2$ so substitution of $g$ into the energy equation gives: $E=GMmh/... 3answers 206 views ### Was Aristotle Actually Correct About Gravitation? [duplicate] Apparently, Aristotle reasoned (without experimentation) that heavier objects must fall to Earth faster than lighter objects. For example, a 1,000 kg ball of iron would fall faster than a 1 kg ball ... 1answer 295 views ### Falling dominoes I have been attempting to determine the maximum velocity a line of dominoes can reach. I have found that there are two forces which act upon it: Initial impulse and gravitational force. As kinetic ... 1answer 243 views ### Is there always an equilibrium point in space for gravity? For instance, for a two-body system, there will always be a point in-between the two in which the forces of gravity completely cancel, and if I were there then I would experience no net force. I ... 1answer 354 views ### Could fish in plastic bags filled with water float like that? I saw this gif earlier and it bothered me how the plastic water bags with fish in it are not submerged in water like they would if we don't do anything special with the water inside and outside the ... 5answers 9k views ### Why aren't there spherical galaxies? [duplicate] According to the Wikipedia page on Galaxy Types, there are four main kinds of galaxies: Spirals - as the name implies, these look like huge spinning spirals with curved "arms" branching out ... 2answers 604 views ### Hourglass on the Moon Someone asked me this, and I was surprised to find I couldn't answer it: suppose I have an hourglass / egg timer that times two minutes in Earth's gravity. If I used it on the Moon, how long would it ... 8answers 6k views ### “Falling upward” - how far you have to be from Earth to start falling to the Moon? Talking about gravity with my 9 y/o she asked when do we start "falling upward" to the Moon. What is the distance at which the Moon's gravitational attraction is higher than that of the Earth and thus ... 2answers 138 views ### Could one make steel balloons? [duplicate] Reading this question reminded me of an idea I once had, and I wonder whether it's feasible. Imagine a hollow ball made of something strong, like steel. Imagine there is nothing inside; only vacuum. ... 2answers 243 views ### How can Rosetta spacecraft orbit an object with such a low mass? Comet 67P Churyumov–Gerasimenko's mass is 11 orders of magnitude lower than Earth's. That means that the comet's gravity force is also weaker than Earth's in the same proportion. Provided that also ... 4answers 451 views ### Car driving / falling off of a cliff - will it land upright? In a recent episode of The Walking Dead, a van was pushed off of a bridge and flipped once and landed upright, on all four wheels. Assumption: the ground and cliff are both flat. Will a vehicle ... 1answer 203 views ### Rate of acceleration for two hanging masses in two experiments I conducted an experiment where two masses of different weight were attached by a string and fed through a pulley. The difference between the masses was$0.025\: \mathrm{kg}$. The lighter mass was ... 1answer 88 views ### Newton's gravity formulas for ellipses A few times I've come across formulas, which are identical for circular and elliptical orbits, except that for the second ones you substitute$r$with$a$, where$r$is the radius of a circular orbit ... 1answer 173 views ### Direction of gravitational field in Hemisphere Supposing we have a uniformly mass distributed hemisphere of some radius, so what will be direction of gravitational field throughout the flat surface of hemisphere? And why? 2answers 1k views ### What is the weight of the Philae lander on the Churyumov–Gerasimenko comet compared to earth? We know the payload mass of the Philae lander was 21kg. We know the mass of the Churyumov–Gerasimenko comet is roughly 1 x 10^13kg. We know the mass of Earth is roughly 5.9x10^24kg. I've heard ... 2answers 158 views ### How is the most accurate value of$G$measured? How do modern scientists update the measurement of$G$, the gravitational constant? Is CODATA the authority on this measurement and the experiment? 7answers 478 views ### Could Galileo ever prove that$g$is the same for a feather and a hammer? Do you think he could have possibly found a way to make a feather and a hammer touch ground simultaneously, as they should, according to gravity? Can you make up a device that avoids air resistance? ... 1answer 302 views ### How would the Sun's gravity affect us if we weren't in orbit? So since we're in orbit around the sun, we are basically in free-fall. From what I understand, this means that we don't feel the gravity of the Sun like we do the Earth. Just like astronauts on the ... 4answers 174 views ### Solar vs lunar gravity: inverse square law Bearing in mind the moon's perfect fit when eclipsing the sun, were the two orbs to have the same density, would they not each exert the same gravitational pull on the Earth? (Much like a dim star in ... 3answers 231 views ### Angular momentum The satellites are revolving around a planet in circular orbits by themselves (no external source to maintain their speed). Are we able to make them revolve in elliptical orbits by themselves? Do ... 1answer 505 views ### Philae lander simulation off by factor of ~3 I'm trying to simulate the Philae landing by writing a program to compute the position of the lander vs time. According to various mission websites, the orbiter will match its orbit to the rotation of ... 5answers 7k views ### Build a ring around Earth, then remove the supports What would happen if we decided to build a giant ring that managed to wrap around the whole world, end to end that was supported with pillars all along the ring and then the supports all suddenly ... 1answer 47 views ### Why do we have to use an integral in this scenario to figure out$v_{max}\$? [duplicate]
$$\int_0^R mg\frac{r}{2}dr=\frac{m}{2}v_{max}$$ and can't write $$\frac{m}{2}v_{max}=mgR$$ don't we usually equal potential energy to kinetic energy? A stone is falling through a tunnel towards the ...