Suddenly, you start floating and everything around you is drifting away from the floor. You try to grab hold of a lamp post, but too late, you realize that it’s floating too. You look around frantically and you see water rising and floating out of the once existing lake. You try to find something to clutch, but you drift away faster and faster from the Earth’s grasp and into outer space. As you wake up from this unpleasant dream, you realize how lucky you are to have gravity keeping you safe and sound here on planet Earth.
In my article, I will be talking about what gravity is; the reason why planets have different gravitational pulls and what that means; and finally how our planets stay in orbit.
What is Gravity?
Gravity is the force that pulls an object with mass to its center. Every object and living organism on Earth is pulled towards its core. This means that the seat you are sitting on is being pulled towards the core of the Earth. The picture below shows how the force of gravity works.
Gravity was discovered by Sir Isaac Newton. He was sitting under an apple tree when suddenly an apple fell on his head. He pondered why the apple had not gone sideways or upwards but had instead fallen down. He then realized that gravity, the invisible force, was the answer. His theory on gravity is
This means that gravity depends on mass and distance.
The characteristics of gravity are that (a) it is one of the four fundamental forces of nature, (b) all objects with mass have gravity, and (c) that gravity only pulls but never pushes.
The Reason why Planets have different Gravitational Pulls
Gravity is a property of matter . Objects with larger matter will have stronger pulls than smaller objects. Let's take two examples: Mercury is about one-third the size of the Earth. Mercury’s gravitational pull is therefore weaker than Earth’s. But, if we take Jupiter which is about thirteen times the size of the Earth, Jupiter’s gravitational pull is much stronger than the Earth’s because of Jupiter’s larger mass. The pictures below show the size of Earth relative to Mercury and Jupiter
If you were standing on Jupiter, you would be completely flattened onto its surface. But, if you were standing on Mercury you would be able to jump nearly 3 times as high as you could on Earth. If you weigh 1 kilograms on Earth, you would weigh 2.3 kilograms on Jupiter and 0.3 kilograms on Mercury, all because of the difference in gravity.
How our Planets stay in Orbit
As you may know, the Earth and all the other planets in our solar system revolve around the sun. The solar system was formed by a rotating disk-shaped cloud that spun around the sun at its center. This spinning disk-shaped cloud formed all of our planets. The gravity of our sun keeps our planets in orbit because the sun has the strongest gravity in the solar system. The reason why the planets do not get sucked into the sun is because each planet has its own gravity which resists the sun’s pull but not completely. The balance of gravitational pulls of the planets allows all the planets to keep their orbits around the sun. This means that if there was a change in the gravitational forces of the sun and any planet in our solar system, the orbits would also change. The picture below shows the planets in our solar system aligned in their orbits around the sun.