Our Solar System
Gravity is the force which draws any object back to the ground. For example, when we jump, we don't float up or sideways. We are pulled back to land on the ground. Gravity causes objects to have weight! More gravity, causes an object's weight to increase. Less gravity causes the weight of the same object to decrease. So a 450 grams AFL football weighs:
> 1.2 kgs on Jupiter
> 12.5 kgs on the Sun
> and just 74 grams on the Moon.
Why is gravity different on other planets?
Gravity depends on mass of an object. The more dense the mass of a planet or a star is, the bigger its gravitational force will be. Mass is the amount of matter in a planet. This is different to the weight of a planet.
What were some early views about Gravity?
Aristotle (384 - 322BC), was one of the first to claim that all objects have a tendency to move towards the center of the Earth - even the moon, the sun and the planets he believed, orbited around Earth. While not entirely true, because Earth and other planets orbit the sun, he brought humankind one step closer to the concept of gravity.
The leaning tower of Pisa, Tuscany, Italy
Galileo (1564 - 1642), demonstrated that gravitational force pulled objects to the Earth's core at a consistent rate. He dropped two similar shaped balls of different masses from the top of the leaning tower of Pisa, and proved they both landed on the ground at the same time. Until then, it was believed that heavier objects fell faster than lighter objects.
You may be wondering what about a feather vs a Mobile phone - which would land first? The phone would land first purely because of Earth's atmosphere, and air resistance, which would make the feather float. This is why on the moon, where there is no atmosphere, and no air, a feather and a hammer were shown to reach the ground at the same time, during the Apollo15 moonwalk.
Isaac Newton (1642 - 1727), is probably what many people think of as the person who discovered gravity. Legend says Newton noticed the existence of gravity when he saw apples falling from a tree. And he noticed that they accelerated as they fell toward the ground, thus theorizing that any object will always fall towards the center of the Earth, concluding that there was a force compelling them to do so. That force was Gravity.
Fun fact: Newton did not use the word Gravity first. It was already in use to describe a quality. Newton however, crucially shifted the meaning of the word.
Many other scientists, such as Kepler and Robert Hooke, have mentioned gravity, and there has been much debate about gravity since ancient Greek times. It seems that human beings were aware of its existence at a very early stage.
Newton has compiled and published his thoughts on force and movement in the book "Mathematical Principles of Natural Philosophy". This is a very epoch-making content and is said to be one of the most important works in modern science.
So how does gravity actually work?
When talking about gravity, you will hear of terms such as centrifugal force, attractive force, Einstein's theory of general relativity and spacetime, Quantum Mechanics and Quantum Physics, Loop Quantum Physics, String theory and more. But regardless of all this, we don't yet truly understand how or why gravity works. We just know that the force of gravity exists in this universe, otherwise life would never have existed on Earth. It keeps the Sun, Moon, and, the Earth from bumping into each other. It is not just our planets that gravity keeps in place, but the whole entire universe, in all its inconceivable vastness that ticks along perfectly, because of Gravity. Incredible!
Gravity in action
Scientists today are continuing the quest to answer the knotty question of what exactly gravity is. One day in the not too distant future we will know for sure.
For now, we should be comforted by the knowledge that Gravity is all around us. It is an invisible force that keeps everything on earth from floating away to space. If you love to float however, check out the antigravity machine here.
Just messing with Y’all. I haven’t made one yet :)