Naked Science Forum
On the Lighter Side => Science Experiments => Topic started by: thedoc on 16/01/2014 14:30:01
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Amelia asked the Naked Scientists:
I was doing a simple physics experiment with my 7 year old home school son when the question came up about Gravity. What is gravity?
As I read along the explanation of gravity and the forces that hold up a cardboard underneath a glass full of water I began to doubt the explanation given in this particular book.
As I ponder and questioned their theory that gravity from earth pulls and that the pressure as the result of air pushing from below underneath the cardboard is what sustained and holds the cardboard against the water. Meaning that the weight of air is higher than the weight of the water inside the glass that is upside down on the cardboard.
I deduced that it is not so much the weight of air pushing on all directions that hold the board up against the glass of water, but rather, the sum total of gravity pulling from other celestial bodies.
What do you think?
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Let us do a calculation, assume the glass is cylindrical 10 cm high and 10 cm diameter.
the pressure of the water on the cardboard at the base will be equivalent to a head of water 0.01 m high pushing the cardboard down whereas the atmospheric pressure pushing the cardboard up will be equivalent to a column of water 10 m high.
There is no need to invoke the theories of Herr Dr Mach
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Amelia asked the Naked Scientists:
I deduced that it is not so much the weight of air pushing on all directions that hold the board up against the glass of water, but rather, the sum total of gravity pulling from other celestial bodies.
Nice experiment. More or less the same principle as chicken waterers and humming bird feeders.
You can sum all the gravity vectors of the Earth, Sun, Moon, and all the stars in the Milky Way. Wikipedia lists the acceleration due to gravity of a few of the celestial bodies (https://en.wikipedia.org/wiki/Micro-g_environment#Absence_of_gravity). Obviously as the Earth spins, the direction of the acceleration due to the other celestial bodies would vary slightly. But, when you sum all the different forces, the greatest force we experience down on Earth is that of Earth, 9.8 m/s2, varied slightly by the different bodies by a few millimeters or picometers per second squared.
Anyway, you know that gravity alone isn't keeping the water in your jar because if you did the experiment without the piece of cardboard, all the water would run out.
Your piece of cardboard creates a seal on top of the glass, and then when inverted, the vacuum created in the jar keeps the water in. The vacuum, of course, being the absence of air pressure.
Our air pressure is about 14.7 psi, created by the column of air above our heads reaching from the surface of the Earth to beyond 100km in space (which it rarefies, but continues somewhat further). I.E. it is that 14.7 psi of air that is keeping the lid on your jar.
Your experiment would fail if you used a pipe filled with water that was 34 feet tall, or a tube filled with mercury 760 mm tall.
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In order for the water to come out of the glass, some air has to go in. The card prevents this from happening.
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It's like the Earth pulling on you and keeping you on the ground. That pull is gravity at work. Every object in the universe that has mass exerts a gravitational pull, or force, on every other mass. ... When you look at really large masses, like the Earth and Moon, the gravitational pull becomes very impressive.
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The question has not been addressed ! there are two main theories about the attraction of gravity one is that it is mediated by virtual particles in a similar manner to the electro magnetic force and the other that the presence of mass distorts space time so that objects take a different path thru it.
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there are two main theories about the attraction of gravity one is that it is mediated by virtual particles in a similar manner to the electro magnetic force and the other that the presence of mass distorts space time so that objects take a different path thru it.
Could the two be merged by saying that gravity is a force, mediated by virtual particles in a similar manner to the electromagnetic force and that the maths describing this is equivalent to the maths for a mass distorting space time so that objects take a different path through it?
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What is gravity?
There is a new theory on gravity based on entropy, it supports the MOND curve fits that dont need dark matter to explain why the movement of the outer parts of galaxies. Here is a link to a lecture on emergent gravity by prof Verlinde https://insidetheperimeter.ca/a-new-view-on-gravity-and-the-dark-side-of-the-cosmos-erik-verlinde-public-lecture/?__hstc=261081490.b20e624ce3bbf82fcde9c8f1a30c5bc1.1533466440658.1533466440658.1533466440658.1&__hssc=261081490.1.1533466440658&__hsfp=2495466239
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[i[What is gravity? [/i] - Gravity is a force which acts only on other objects which have mass, which seems to be everything, Gravity is created by gravitational squires such as mass (other things if you take general relativity into account)
If would be help for you to look up the definition pf gravity. Gravity is a phenomena where gravitational force is act.
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Qouting from wikipedia. https://en.wikipedia.org/wiki/Entropic_gravity
"Entropic gravity, also known as emergent gravity, is a theory in modern physics that describes gravity as an entropic force—a force with macro-scale homogeneity but which is subject to quantum-level disorder—and not a fundamental interaction."
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If you look at the suggested videos after this one ends, there is at least one which explains exactly how this was done.