Asked by tibi29 to Denise, Daniel, Anna on 26 Jun 2014.
Keywords: future, gravity, power
very interesting question. The gravity force between two objects, let’s say me and the Earth, depends on 4 things: the two masses of the two objects (my mass and the mass of the earth), the distance between the two objects (better, the distance between the centres of mass of the two objects) and G, also called gravitational constant, approximately 0.0000000000667 N·(m/kg)^2 ( note: scientists always have to put units nearby numbers, unless they are dimensionless, so in case you do not know one or more of these units, ask me or your teacher! however, it is not a crucial point here).
This G is, in fact, a universal constant, that means it has the same value in the whole universe (or at least, we believe so). Knowing this, I can now try to answer your question.
If we remain in this universe, and the two objects do not change their mass or their relative positions, gravity force will stay constant.
If one of the two objects gains mass (for example, I eat 5 cakes) then the force that attracts me to the earth will increase (in fact, my weight will increase!) but if I move distant enough from the centre of mass of the Earth, than the force of gravity will also decrease, until I can escape the atmosphere and float into space.
The same mechanisms applies on me going to the Moon. The Moon has a smaller mass compared to the Earth, that’s why if I’ll be walking on the Moon I ‘ill be able to jump very high, and my weight will be..8.3 kilos, according to this website
(how about yours?)
so gravity force will be less, but the gravitational constant remains… well, constant 🙂
Interestingly, because of the shape of the Earth, the local gravity force can also vary from place to place on Earth , because you are at different distances from the centre of mass of the Earth: this means your weight can change according to where you are (although very very little: you weigh about 0.5% more at the poles than on the equator)
It will be completely different in another universe, where G could have a different value. This will lead to a complete different physics governing planets and stars motion, but many other things will change as well, for example your weight, the average hight of trees, or of animals, that would have to deal with a different gravitational force, and many other things.
This sounds actually a lot of fun, it would be nice to try to calculate some planets trajectories with different G-values…
Scientists have long known that blackbodies produce radiation and that radiation creates a repulsive effect. However, according to a new study there’s another force at play, one that acts a bit like gravity and attracts objects to the blackbody. They’re calling it “blackbody force.”
Blackbodies, celestial objects that are perfectly non-reflective, shift the atomic energy of molecules around them in what’s known as the Stark effect. This occurs when the electric field created by the blackbody radiation sends photons into surrounding molecules and atoms that often create the repulsive energy we’re used to seeing around blackbodies. However, if the energy level of the photon is just right and the radiating blackbody is less than about 6,000-degrees Kelvin, it creates an attractive force that’s greater than the radiation pressure and, in some cases, greater than the force of gravity.
This new blackbody force only affects the smallest particles in the universe, though it has an effect on basic astrophysical scenarios.
Hope it helps! 🙂
The force of gravity depends on the mass of objects. The Sun has the largest gravitational force in our Solar System because it is the most massive object. Of the planets, Jupiter has the largest gravitational force. Because gravity depends on the mass of objects, if there is no change of mass or distance betwen the objects, there is no change in gravity. Now, on planets there are subtle differences in the force of gravity called gravity anomalies. These differences occur when you have changes of mass, for example next to mountain belts (you have more rocks that form the mountains) and valleys (you have less rock compared to the mountains). Geoscientists have used gravity anomalies to find mineral deposits under the surface. Metellic bodies would be more massive than the surrounding rock and would produce a positive magnetic anomaly.
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