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Hi I am a high school physics student and I am currently struggling to grasp the concept of Newton's law of universal gravitation.

I am really confused with how this works. So do all objects attract each other with a force of gravitational attraction?

So when I am looking at my laptop which is stationary on a table, there is force of gravitational attraction between me and the laptop?

If so, how come I am not attracted to the laptop, like how come I am not moving towards it?

So does Newton’s law of gravitation apply to any and every object in the universe, no matter the size and the mass?

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  • $\begingroup$ Related video $\endgroup$ – BioPhysicist Feb 25 '20 at 1:40
  • $\begingroup$ Mass always generates a gravitational field. All objects attract each other, but the "G" in Newton's law of universal gravitation is so small that there is no way to notice this force of attraction for objects that are substantially smaller than a planet. $\endgroup$ – David White Feb 25 '20 at 1:45
  • $\begingroup$ PSE post about that related video: Newtons law of gravity universal? $\endgroup$ – BioPhysicist Feb 25 '20 at 1:54
  • $\begingroup$ @DavidWhite Hey Dvid thanks for the comment! I just wanted to ask what is "Mass always generates a gravitational field" theorem/law called? I want to do some research. Many thanks. $\endgroup$ – GoNK Feb 25 '20 at 2:04
  • $\begingroup$ @FredWeasley, in my opinion, it's just a fact of nature. Recent physics research on the Higgs boson may have dealt with why mass generates a gravitational field, but I'm not up to date on the Higgs boson. $\endgroup$ – David White Feb 25 '20 at 6:22
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So does all objects attract each other with a force of gravitational attraction

So when I am looking at my laptop which is stationary on a table, there is force of gravitational attraction between me and the laptop?

So does the newtons law of gravitation apply to any and every object in the universe, no matter the size and the mass?

In the context of high-school physics: Yes to all of these.

Of course, later you will learn that Newtonian gravity is an approximation to General Relativity, which is itself expected to be an approximation to an undiscovered theory of quantum gravity. But to the best of our knowledge all objects interact gravitationally, regardless of their size.

If so how come i am not attracted to the laptop, like how come am i moving towards it?

You are. It is instructive to approximate the magnitude of the force. Suppose that you mass 70 kg and the laptop masses 1 kg. Approximate both as point masses located 50 cm apart. The gravitational force is then about 19 nN. This is far less force than is exerted by the laptop’s fan exhaust, maybe not even enough to move a grain of dust against friction.

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  • $\begingroup$ I think the first part of the answer should be "all massive objects interact gravitationally"? $\endgroup$ – Allure Feb 25 '20 at 3:28
  • $\begingroup$ @Allure Massless objects also interact gravitationally. In fact, radiation is an important source of gravity in the Friedmann equation used in the current cosmology model, and some pp-wave spacetimes also describe the gravitation of massless radiation. So massless objects not only experience gravity but they are also valid gravitational sources. $\endgroup$ – Dale Feb 25 '20 at 16:34
  • $\begingroup$ @Dale would the distance be the distance between the centres of the 2 objects or the surface of 2 objects? Is that what "point masses" refer to? centre of 2 objects? Sorry i am new to the terminology. Many thanks! $\endgroup$ – GoNK Feb 26 '20 at 2:59
  • $\begingroup$ @FredWeasley Yes, the easiest approximation is to consider the two objects as though all of their mass were concentrated at the center of mass of each object. If you don't make that simplifying assumption then you have to integrate the force law over the object. It can be done, but the math gets messy fast, and it will be a small correction to an already small effect. $\endgroup$ – Dale Feb 26 '20 at 15:45

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