Things with mass and/or energy are attracted together by a force that we call gravity (F = ma, Second law of motion). The feeling of gravity is just you and the earth being attracted to one another and every portion of an object, with mass, attracts other portions towards it. The average of all this pulling is an attraction between centers of mass. Giant things like Earth exert an obvious pull, but everything does. Even small objects such as tennis ball.
Two tennis balls are attracted together by their own gravities, except their masses are so small, the force is minuscule, and it can’t overcome friction or push air out of the way. But they’re never gonna come together. But, if you put two tennis balls one meter apart in the middle of empty space, where no other forces could act on them, they would literally fall together and collide.
Isaac Newton found (Newton’s law of universal gravitation) that the strength of the force bringing two things together is equal to:
Product of their masses
Distance between their centers of mass squared
The gravitational constant, G (6.674×10−11 m3 ⋅ kg−1 ⋅ s−2)
When you make one of two objects more massive, or move them closer together, the force will be stronger and this force of attraction is what we call weight. But because the Earth’s mass is so much greater than our own and because the more massive something is the more it resists being moved.
So, if you drop a pencil from a height of 2 meters the pencil doesn’t just fall to the earth, more precisely: they both come together.
They’re attracted to each other by equal forces, but the same force moves the pencil a lot more than the earth. When you let go of the pencil the earth is literally pulled up to the pencil by the pencils own gravity a distance equal to about 9 trillion the width of a proton. That same force moves the pencil the remaining distance, which is still pretty much 2 meters…
Many experiments have confirmed general relativity’s picture of the universe fitting the conclusion that there is no gravity, there’s just space-time, its curvature and us in it.
As John Wheeler famously put it:
Space-time grips mass telling it how to move and the mass grips space-time
telling it how to curve.
Relative to the earth, we don’t move very fast. Even jet airplanes move negligibly close to the speed of light. So relative to earth we move almost exclusively through time, as such we are more affected by the way time is curved by mass than how space is curved. This has led many to claim that for the most part you feel, as though, you’re being pushed into the ground not because of a force called gravity but because time is moving faster for your head than for your feet. Down is relative and always changing, but it exists because of and is always in the direction of slower time. Everything is naturally steered towards where time is slowest. We call this falling – going down.
Bertrand Russell called this the law of cosmic laziness.