Lesson 1: What is gravity?
When you jump into the air, you automatically land back on the ground. Apples and leaves fall from trees, and when you drop a glass it breaks on the floor – or have you ever seen one float up to the ceiling? Everything is attracted to the Earth due to the force of gravity.
The word gravity comes from the Latin word “gravis”, which means heavy. Gravity is heavy stuff. The bigger an object, the bigger the gravity force it exerts.
The force of gravity is also present on the Moon. But because the Moon is smaller than the Earth, the Moon’s attraction is not as great as the Earth’s. This is the reason why an astronaut jumping on the surface of the Moon is automatically a long-jump champion – he can jump further than 10 metres!
What is the exact definition of gravity then? A physicist would tell you that it is a force of attraction that arises between objects because of their masses and considered one of the four fundamental forces of nature. But that may sound a bit complicated to you.
In the Universe, this force of attraction exists between all bodies that have a mass. In fact it only means that every bit of matter pulls at every other bit of matter. That means that, because you are a bit of matter, you are actually pulling on your fellow student sitting next to you! But it is only a very, very weak gravitational pull – he or she cannot feel it…
But we all know gravity as the force of attraction of the Earth that works on things near its surface, like an apple, a leaf, or you or your teacher!
The Sun is many times bigger than the Earth and thus it pulls many times more strongly on the Earth. It is because of this pull that Earth orbits the Sun. In the same way all planets (like Uranus, Jupiter, Saturn and the others) feel the attraction towards the Sun and orbit it. Altogether they form the Solar System.
Last update: 7 January 2013