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

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A simple explanation of Kepler's Third Law

Is there a simple way to explain how Kepler's third law follows from the inverse square law that of gravity (and laws of motion) For example for Kepler's second law we can say it's because Gravity ...
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2answers
72 views

Is Keplers First Law a consequence of the conservation of angular momentum?

It would seem that once you have deduced that the angular momentum is conserved then you can deduce: $r^2\dot{\theta}=h$ is constant Combining this with the radial equation of motion then yeilds a ...
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2answers
1k views

Does surface tension play a role in planet's shape?

I'm thinking that when the planets and stars were forming along with gravity surface tension also could have played a role in making them spherical. Am I correct?
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1answer
72 views

Newtonian Gravity Simulator?

Could anyone suggest me a good (and possibly free) Newtonian Gravity Simulator software available on the web, where it might be possible to simulate the Solar System dynamics and playing with it, by ...
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1answer
48 views

Change in energy during orbital decay

Suppose we have a planet orbiting a star and the planet radiates away some amount of energy $\Delta E$. I want to find by how much the orbit decays (i.e the change in orbital radius). One way to do ...
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2answers
48 views

What is the reason for Earth's rotation and revolution?

Is it because of the gravitational effect of the other planets and the sun then why do the other planets rotate and revolve too? And well does the Sun rotate and revolve too?
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2answers
90 views

Why can't we put an object anywhere in the earth's orbit around the sun instead of Lagrangian points?

If we place an object in the earth's orbit around the sun, it should have the same orbital period right? For example, what would be the behavior of an object in orbit at point A1? It is at the ...
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1answer
52 views

Terminal Velocity in Water

Another question concerning classical physics. On Earth, the combination of air resistance and gravity interact in a way that creates the phenomenon of terminal velocity. Do other fluids (for example, ...
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0answers
31 views

What is the equation for the position of a falling body as a function of time? [duplicate]

I know that near the surface of the earth a projectile's position follows a parabolic curve in function of time because the acceleration is constant (about 9.8 m/s2). However, acceleration ...
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4answers
86 views

Would running along Earth's Surface at escape velocity cause you to get out of the Earth's gravitational pull? [duplicate]

If one were to run/drive/fly along the earth's surface (by this I mean tangential to the Earth) at escape velocity (about 7 miles per second), would that person escape the gravitational pull? If not, ...
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3answers
68 views

What does the $k_e$ in Coulomb's law and $G$ in Newton's Universal Gravitation Law mean?

I very well understand the proportionality relation that was used to derive these laws like $F$ is proportional to product of masses and inversely to radius squared and hence its proportional to the ...
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1answer
38 views

If a purely inductive circuit is started in presence of gravity, will the power source ever run out? [closed]

I have read that purely inductive circuits do no work. So if an Inductor with an AC source, coming from an inverter is set up, will the source of power ever run out due to work against gravity? This ...
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1answer
56 views

(Constant) Value Of Gravitational Pull $g$ Of Earth [closed]

I want to know How the value of $g$ was found and what experiments did Newton conduct to land upon the value that we use, which is 9.8 m/s^2. I tried to search for it but I couldn't find much ...
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1answer
61 views

Is it possible to 'push' a path to the Earth's core?

This may very well be a question for Earth Science SE, but as it is very hypothetical, maybe pure physics is more appropriate... Question: Imagine we have have a wedge that tapers down into an ...
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1answer
50 views

Is there an underlying reason why some forces are inversely proportional to the square of the distance? [duplicate]

This is the first time I'm studying those subjects (I'm still in high school) and my teacher couldn't give me an answer. I'm referring specially to Newton's law of gravitation and Coulomb's law of ...
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0answers
12 views

Power Generation Via 2 connected objects below distinct orbits

As an example: Large weight A sits just below Earth's orbit Large weight B sits just below Moon's orbit A, B are connected by sufficiently strong material (may not exist, and if so how much ...
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1answer
58 views

Why does gravity make objects spherical? [duplicate]

Why is it that gravity tends to make large objects spherical? I'm looking for reasons that are based on the laws of physics.
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2answers
2k views

Throwing a Football. Is it truly parabolic?

Driving into work, I started thinking about the arc of something being thrown and was puzzled about how gravity's affect is squared per second for falling bodies. Intuitively that implies the shape ...
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1answer
64 views

Gauss law in gravitation

Is it possible to use Gauss's law of electromagnetism, (The net electric flux through any closed surface is equal to $1⁄\epsilon$ times the net electric charge enclosed within that surface.) to ...
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1answer
160 views

Would a non-rotating Earth collapse on the Sun?

If the earth stopped rotating on its axis, would this influence its revolution motion? In particular, could it collapse on the sun? I ask this because on the one hand I thought the two degrees of ...
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1answer
43 views

Will the Earth ever show synchronous rotation? Why and when?

In this answer to the question "why does the moon have the same rotation and revolution periods?", we read: The mass and speed of rotation of the Earth influence the moon in that some of its ...
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3answers
136 views

Newton's gravity vs Einstein's gravity

Hello so if i were to simplify the difference between gravity as seen from Newton and gravity as seen from Einstein, could i say that Einstein's gravity is just adding the fact that gravity does not ...
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1answer
40 views

Conservation of energy in the “ideal physics world”

Let us assume we are in the textbook ideal physics world, without any friction. Now, if I place a ball at the top of a parabola U and let it go under gravity, the ball should roll up and down forever ...
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2answers
95 views

How to find speed of rotation of gears from kinetic energy of falling body?

A pulley is fitted to the first driven shaft of compund gear train. Last driven shaft of gear train(gear 8) is fitted to the 12V DC generator (6W).Now to the rope extension at the one end of the ...
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0answers
34 views

Pendulum in radial gravity field

All I could find about pendulums assumes that the force on the pendulum mass m is mg directed downwards. The case of m being attracted only by the radial gravity pull (thus replacing the "plane" ...
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2answers
64 views

Planets potential [duplicate]

I'm a physic student of Italy. I'm moving my first steps in this beautiful world, and as every new entry, my simple and stupid questions are sometimes not so simply resolved. I'm trying to know the ...
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0answers
34 views

Semi-major axis , specific mechanical energy, its period and velocity at Apogee and Perigee and what the difference is [closed]

Hi im needing some help with two questions could you please show the formula and the way its solved?Thanks PS:Could you also explain what the difference of velocity and apogee and perigee? 1.)A ...
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2answers
115 views

In what direction should you throw a 1Kg uniform sphere in order to put it into lower earth orbit? [closed]

If you are standing on earth's surface, in what direction (and at what speed) should you throw a 1Kg uniform sphere of radius 0.1 meters in order to put it into lower earth orbit? Assume that there ...
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2answers
73 views

Why do we take $h$ as “height from surface to bottom” when calculating liquid pressure?

In the following image, pressures of points x, y and z are $P_{x}, P_{y}$ and $P_{z}$ respectively, and they all are equal. My question is, why? The amount of matter on x is much more than amount of ...
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1answer
36 views

Motion under gravitational forces

In a system of particles, can a particle be considered to be attracted to the combined center of mass of the other particles if the Newton's universal law of gravitation is used (the inverse square ...
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1answer
305 views

What is the difference between gravitational force and gravitational field?

I see two different formulas describing gravity: $$F=\frac{GMm}{r^{2}}$$ $$g=\frac{F}{m}$$ But I don't understand the difference between gravity as a force and its field as a vector.
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2answers
46 views

Parachute Model

Can you tell me if this model is correct or not? [assuming drag is linearly proportional to the velocity] Considering y-axis vertical and x-axis horizontal,with y positive upwards: 1) ...
1
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1answer
49 views

Force felt by parachutist when opening the parachute [closed]

When falling down with air resistance, y-axis vertical (positive is up), x-axis is horizontal, we have that: $F_y=-mg-kv=ma_y$, where $k$ is the drag coefficient. Now if the man opens the parachute, ...
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1answer
48 views

Hot air balloon trajectory predictions

Hey there Physics friends! I've been struggling with what seems to be a very basic physics question. Let's say that I have wind vector for a given altitude and location, and I want to calculate the ...
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5answers
93 views

How can escape velocity and gravitational potential be higher in weaker gravitational fields?

on Earth we have an escape velocity of about 11180 m/s and a gravitational field of g=9.81 m/s^2. It would seem obvious that the escape velocity was higher for stronger gravitational fields. Often it ...
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1answer
42 views

Free fall vs throw with air resistance

If I let a stone drop from a certain height and throw a stone from a certain height, with air resistance, which will reach the ground first? When I draw a free body diagram the air resistance in the ...
3
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3answers
77 views

Could the Earth-Moon rotation period equal one Earth year?

I just stumbled on this rather confused QA. The point seems to be if the Earth-Moon rotation period was identical to the Earth-year, then ... ... all three would stay in a line at all times. ...
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5answers
86 views

Solving for $r=0$ in an inverse square law

This occurred to me in thinking about Coulomb's Law for a spherical insulator, but obviously can be asked of any inverse square law force calculation. For example, all things on the surface of he ...
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2answers
58 views

The shortest path among two points inside Earth [closed]

I have this idea and I don't know how to process, explain or question it. I hope you can understand these images and help me formulating a good question. This is like a gravitational train but it ...
1
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4answers
89 views

Gravity and force

I have a question and am not able to answer it. Suppose you drop two objects from different heights. They are exactly the same shape, size and weight. Now we know that the gravitational acceleration ...
1
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1answer
93 views

Distance from Earth where gravity becomes negligible

This is a basic little problem I thought up when trying to remember some physics, and I wanted to see if it's at all correct: trying to figure out the distance from earth where gravity becomes ...
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0answers
21 views

Gravity changes at the equator due to Earth's spin [duplicate]

If an object weights 100 kilos at the equator how much would it weight if the earth spun twice as fast?
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6answers
6k views

How does a spinning object “know” that it is spinning?

I am constructing a thought experiment about a spinning object that is floating in intergalactic space. I assume that this object is about the size of a planet so that it will have enough gravity so ...
3
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2answers
51 views

Where is the space elevator falling? And the cable holding it?

I guess the concept of a space elevator is pretty well known. The idea, first published by Konstantin Tsiolkovsky in 1895, and popularized (among others) by Arthur C. Clarke in The Fountains of ...
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0answers
31 views

Blackhole and light [duplicate]

I was talking with my friend about blackholes and I asked him "Why blackhole 'sucks' the photons?" He had no deeper understanding so he answered that "I dont know, may the light is affected, because ...
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1answer
43 views

Forces in a body falling with air resistance

I would like to know why when a body falls with air resistance, we have that the drag caused by the air is -kv and the acceleration is -mg. What I don't understand is how they both have the same sign ...
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0answers
24 views

Relation between gravitational field and gravitational potential

gravitational field is the negative differential of gravitational potential . now gravitational potential due to a particle at a distance r is -Gm/r where m is the mass of the particle . If i take the ...
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3answers
129 views

Using normal rules of gravity, How would gravity work on a flat “world”?

The question is a bit vague, so let me provide some more context. Imagine we have a world like Middle-earth (prior to the end of the Second Age), or any of many fictional Fantasy worlds (Glorantha, ...
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0answers
22 views

How to calculate the force of pull when a high speed rotating wheel is braked suddenly and immediately accord to angular momentum?

According to angular/circular momentum, how can I calculate the force of pull when a high speed turning wheel is stopped suddenly and immediately (I mean stop to 0 m/s within 0.1 sec). As I know, this ...
3
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2answers
108 views

When a rocket or car is accelerating is the air in it going backwards or not?

I'm not sure but when a car is accelerating is the air in the car pushed backwards or not? If so why did Einstein say that there is no way of finding out (besides tidal effects) the difference ...