What is Gravity?

You attract the universe, and the universe attracts you.

Everything you see, and everything you don’t, as long as it has a mass, is affected by gravity.

From the phone sitting next to me as I type this, to my cup of tea. From me to Jupiter, nearly 465 million miles away (driving 60 mph, it would take about 885 years to get there).

Everything, even your cat, is affected by gravity.

Gravity is one of what are called the 4 Basic Forces, and has an absolutely infinite range. As the distance between things increases, the effect of gravity decreases. It might be so low it’s virtually impossible to detect, but it’s never gone.

Isaac Newton, who we’ve talked about before, looked to the night sky to try and figure out why the stars and planets moved the way they did. What he discovered is the gravitational force between two objects depends on the masses and the distance between them. He called this relationship the Universal Law of Gravitation

More massive objects, like stars or black holes, have a stronger gravitational pull. The closer two objects are together, the stronger their gravitational pull. Move them apart, and the attraction will decrease.

Okay, so how come my teacup isn’t orbiting my head? Why am I not being yanked towards the sun?

Simple. The earth is the only thing that is both close enough and massive enough that I can feel its gravity. The teacup has some, but it isn’t massive enough for me to notice, and I’m not massive enough to overpower earth’s gravity and create my own Mary Poppin’s type orbit in my kitchen.

Besides, gravity may be infinite, but it’s also finicky. Let’s imagine two objects out in space just one meter apart. Move them apart one more meter and the force of gravity between them will be just 25% of what it was!

You can think of all of this in terms of rings of force around every object that decrease in strength the farther they reach. We call these gravitational fields. Gravity reaches out from the center of every mass, pulling things towards its middle. Reaching out from the middle in all directions means that the field is a circle, or a sphere.

Ever wonder why star and planets are round? All things are pulled towards their middle from all directions. What might start as a jumble of pebbles may eventually become a planet. All that stuff in the middle is now under so much pressure it heats up into a hot, molten core. As the ball continues to grow, its gravity increases!

Planets are round because of gravity!

On earth specifically, you can see evidence of this in the make-up of the planet. The densest of things are located close to the center, like nickel and iron. Less dense things, like water, sit mostly at the surface!

If all of this is still hard to imagine, think about sitting on a trampoline. Imagine you sit directly in the middle and someone sets a ball on the edge. What will that ball do?

It will roll towards you!

Imagine two people on the trampoline. One is much heavier than the other. They will pull the trampoline down towards the ground more. The closer the other person is to them, the more they will slide towards them.

That’s how gravity do.

Try this at home

1st you’ll need an old coffee can, a large bowl, or even a round garbage can.

If you’re using an old coffee can, find a t-shirt or another thin piece of cloth and place it over the top. Use a rubber band or string to make sure the cloth is nice and tight around the top of the container. Now experiment with anything from marbles to sand or even ping pong balls. If you’re scaling it up, you can use a stretchy cloth, like lycra, over a garbage can and use billiards balls and golf balls to experiment with how the mass and distance of objects will affect others around it!

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