Tagged Questions

70 views

Universal gravity at small distance

Could it be that there is simply a maximum gravitational force that two bodies of finite mass can exert on one another? This would occur at $r=0$, so maybe there is some really really really small $a$ ...
186 views

Does the mass of a star change as it collapses into a black hole?

I know (I think!) that when a really big star collapses on itself it creates a black hole. My question: When a star collapses, is the mass equal to the mass of the star when it's not a black hole? Or ...
75 views

Gravity force between two objects with different mass

We know thanks to Newton that: $$F=G\frac{m_1\cdot m_2}{r^2}$$ Where $G$ is the Gravitational Constant that is about $6.673\cdot10^{-11}$ $m_1$ and $m_2$ are the masses of two different objects ...
36 views

Gravity force and dark energy [duplicate]

If gravity is a fundamental force which bends spacetime and dark energy is energy which stretches spacetime, what is the difference between the terms force and energy?
84 views

Is gravitational force affected by intervening medium?

If we leave a iron ball and feather into the water, feather returns to the surface and floats or moves into the water slowly. On the other hand, iron ball (of certain mass greater than mass of ...
76 views

Force acting on center of mass

Pictured above is a biker (traveling in a curve) whose center of mass has two forces acting on it. These two forces - a horizontal centrifugal force F(centripetal)* and a vertical gravitational ...
84 views

What happens to gravity in the middle of the earth? [duplicate]

So I was curious about, what if we make a tunnel from one side of the earth, to the other side of the earth? Gravity is ofcourse always negative, which makes you "fall" and not "float". If we take ...
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How to measure power used to sustain something in a (gravitational) field? [duplicate]

I've read this question and answers, but neither of the posts does seem to address my concerns. The problem is as follows: Assuming a device that keeps something in a gravitational field on a ...
67 views

The nature of the gravity force: Is it attractive or repulsive between positive and negative mass? [duplicate]

If negative mass is rotating around fixed positive mass, then what will be the nature of force and how?
214 views

Why meet at the center of mass?

If two objects of different masses are held at a distance $d$ and then I let them go, they will meet at the center of mass of the particle system due to mutual gravitational attraction My question ...
300 views

Can we escape earth's gravity slowly?

I had a recent conversation with my girlfriend, who is a physics grad student. She was kind enough to listen to me rant about an idea concerning escape velocity. Unfortunately, I am still thinking ...
64 views

Blimp challenge. Doubts about volume at different heights [closed]

I want to design and build a small semi-rigid airship/dirigible. It will be controlled with RC so I will install motors, arduino, battery etc. Filled with helium. Weight of the equipment is about 2kg ...
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Solids: is energy expended in some fashion by, say, a table to keep the top from sinking down against gravity?

A friend and I were discussing this, and couldn't decide. Since it takes energy to physically raise something up above the planet's surface, does it continue to require energy in order to keep it ...
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Rotating sphere and circular trajectory: minimum speed

I have a sphere (mass = 3 kg), constrained to a fixed length rope, rotating (radius = 5 m) on a vertical plane. My textbook ask me about the minimum speed in the highest point in order to keep the ...
632 views

How to measure force of impact inside container?

I am in 7th grade and for my science fair project, I need a way to measure the force on a dropped object when it hits the ground. What I am trying to determine is which packing materials provide the ...
965 views

is gravity always the weakest force [duplicate]

Possible Duplicate: What does it mean to say “Gravity is the weakest of the forces”? Strongest force in nature It is usually taught that the gravitational force is the weakest ...
2k views

If the earth would stop spinning, what would happen?

What would happen if the earth would stop spinning? How much heavier would we be? I mean absolutely stop spinning. How much does the centrifugal force affect us? If you give technical answers (please ...
859 views

Why doesn't a fly fall off the wall?

Pretty simple question, but not an obvious answer at least not to me. I mean you can't just place a dead fly on the wall and expect it to stay there, he will fall off due to gravity. At first I ...
903 views

Where does the “g” force that pilots experience come from?

I understand that it has to do with acceleration. Say a pilot does a quick maneuver and experiences a force of 5g. What exactly is happening here? And what is this force relative to? If someone ...
164 views

Could this fountain, under the right conditions, technically be able to lift me up?

There is a big fountain in a lake in my city. I was talking with a friend and we were wondering whether it would be able to lift me up. I sent a few emails and obtained information about the ...
149 views

detect movement - how does it relate to G force

I would like to detect if a user is moving by using an android smartphone - walking or jumping doesn't matter - want to know if the user wearing the smartphone is moving. I have found this code ...
633 views

Gravitation is not force?

Einstein said that gravity can be looked at as curvature in space- time and not as a force that is acting between bodies. (Actually what Einstein said was that gravity was curvature in space-time and ...
250 views

How do we end up with a gravity-dominant macroscopic universe from a quantum world having weakest gravity?

At quantum scale, gravity is the weakest force. Its even negligible in front of weak force, electromagnetic force, strong force. At macroscopic scale, we see gravity everywhere. Its actually ruling ...