Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: McQueen on 13/05/2021 15:53:10
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Unfair shift to New theories. This is my new theory. Bye
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Since in a gravitational field, weight is the same as mass, this seems to be a self-defeating explanation.
Not really, as gravitational fields come in different strengths. Your weight on Earth is different than your weight on Mars, whereas the mass is the same on both planets.
Why do objects in free fall within the earth’s gravitational influence, still fall to earth with an acceleration of 9.8 m/s2 even though there is apparently no force acting on them.
There is a force acting on them.
The inertial mass exactly matching the gravitational mass, the two masses should cancel each other out
That's not how math works. Two equal numbers adding together do not sum to zero (unless the numbers you started with were zeros).
leaving a net zero force acting on them
The only way that could be true would be if one mass was somehow creating a force equal to, but opposite in sign, to the other. That's not the case.
Why don’t objects dropped from a height just float instead? This is what happens in the space station where almost zero gravity is experienced.
Not really. Objects in orbit are in freefall. They are not floating.
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No point in posting.
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Why do objects in free fall within the earth’s gravitational influence, still fall to earth with an acceleration of 9.8 m/s2 even though there is apparently no force acting on them.
Newton observed that objects move at constant velocity unless subject to a force, in which case they accelerate. So if an object is accelerating, it must be subject to a force.
Maskelyne rather brilliantly demonstrated the vector nature of gravitational force in his determination of the mass of Schiehallion.
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If the gravity exerted by the Universe were not pulling objects away from the earth with exactly the same force that they are attracted towards the earth, it would not be possible that objects of different weight would fall at the same rate.
No, the reason that objects fall at the same rate is because both inertia and gravitational field strength increase at the same rate as mass goes up. So although Earth's gravity pulls heavier objects more strongly, they have more inertia and thus resist Earth's pull more than lighter objects.
Lastly: could you give me your definition of an object in free fall?
Dictionary.com defines freefall as "downward movement under the force of gravity only."
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No, the reason that objects fall at the same rate is because both inertia and gravitational field strength increase at the same rate as mass goes up. So although Earth's gravity pulls heavier objects more strongly, they have more inertia and thus resist Earth's pull more than lighter objects.
I hope I am not trying your patience. I had wrongly quoted Newton’s third law and have deleted the reference from my post. Your .reference to inertial mass does not offer an explanation of what inertial mass is. Look at this example. Picture an object in space, it could be anything a dinner plate or a cup, the object is absolutely motionless in space, no forces are acting on it. Why? It means that all forces acting on it are in equilibrium. Give the plate a slight nudge and it will continue to move with the same momentum and velocity until acted upon by an external force, as described by Newton. For instance, take the Voyageur spacecraft that are more than 25 billion kilometers from the earth but are still moving with the same momentum that they possessed when leaving the solar system.
Now think back to the aircraft going into a parabolic loop, rendering everything in it weightless. Why does this happen? The aircraft is not travelling at the 27,000 kmh needed to oppose gravity, but it does generate forces that oppose gravity. Normally these are called G- forces but this is probably the wrong term. It is a force, not a gravitational force. Since, gravitational force is about 10 N anything generating a force of more than 10 N will oppose gravity. If the (tidal) gravitational forces are cancelled out, what is left? Whhat is left are inertial gravity and gravity acting exactly equal and opposite to each other, rendering everything not tied down in the aircraft weightless.
This explanation holds up and links everything in a calculable manner to known phenomena and laws.
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The aircraft is not travelling at the 27,000 kmh needed to oppose gravity
Which would be the opposite of what it would need to do in order to make things weightless on board. Rockets shooting upwards into space pin their riders back with extra weight, not weightlessness.
but it does generate forces that oppose gravity.
It's not opposing gravity at all. It's moving with gravity. The plane is effectively falling, just as is everything inside of it. The weightlessness is caused by the fact that everything present is moving at more-or-less the same velocity.
Whhat is left are inertial gravity
I know of no such thing called "inertial gravity". Inertia isn't gravity. It's the tendency for objects with mass to resist acceleration.
This is starting to feel like it is moving into "New Theories" territory. Do I need to move it?
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This is starting to feel like it is moving into "New Theories" territory. Do I need to move it?
Feels like it
All of McQueen’s topics contain serious misunderstandings about the equivalence principle and relativity. You might almost think he has a personal grudge against Einstein ;D
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All of McQueen’s topics contain serious misunderstandings about the equivalence principle and relativity. You might almost think he has a personal grudge against Einstein
I would have to admit that my premise has been wrong and the end result is very much a storm in a tea cup. Newton's equation of F = ma; amply covers the explanation as to why the two are equal even when taken at a very basic level.
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So although Earth's gravity pulls heavier objects more strongly, they have more inertia and thus resist Earth's pull more than lighter objects.
There is not a stronger force on larger objects. It is simply that the force is distributed evenly throughout the whole object. Every proton or neutron has the same mass as any other proton or neutron. The same with electrons. So, effectively, the force is applied at the particle level. The inertia of individual particles does not change.
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There is not a stronger force on larger objects.
I assume you meant "more massive" instead of "larger". If gravity didn't pull more strongly on more massive objects, then everything on Earth would weigh the same, regardless of mass.
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There is not a stronger force on larger objects.
I assume you meant "more massive" instead of "larger". If gravity didn't pull more strongly on more massive objects, then everything on Earth would weigh the same, regardless of mass.
You are forgetting that gravity continues to pull on the object when on a scale. This causes a propagating stress in the object that scales proportionally with mass. Hence the weight is different for different masses. The scale measures the total compressive stress.