Gravity is something we all take for granted. When we drop something it falls to the ground. Just last week an entire packet of spaghetti dropped from its container onto the floor creating quite a lovely sculpture. I can hear my mom, “I’ve seen it all now – a spaghetti sculpture!”
So what exactly is this phenomenon known as gravity that causes everything to drop to earth?
Gravity is an attraction that occurs between all matter. So while there is an attraction between me and my computer (other than facebook!) our masses are too small relative to the mass of the earth to feel it. The earth on the other hand due to it’s huge mass has a gravitational pull on all of us, causing us to stick to its surface.
In 1666, Sir Isaac Newton first stated his theory of gravitation. Here’s for the bit you hated in school:
Newton’s Law of Universal Gravitation states that any two point masses in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
In other words: the greater the mass of two objects, the greater the gravitational pull between them. The further they move away from each other the lower the gravitational pull.
It is the gravitational pull of the Sun that keeps the planets orbiting it. The sun is so massive – weighing almost 2 million billion billion billion kilograms that it has a gravitational pull on Pluto holding it in orbit 5.9 billion kilometres away. Likewise, the gravitational pull of the earth keeps the moon and man-made satellites in our orbit.
The weight of an object is actually a measure of the pull of gravity on the object (Weight = mass multiplied by acceleration due to gravity). The Moon’s gravity is much less than the Earth’s gravity due to its smaller mass. As a result, a baby weighing 6 kilograms at home would weigh only one kilogram on the Moon! I have thought of flying to the moon to weigh myself but my mass obviously wouldn’t change. How crazy would I appear if I told everyone I weighed six times less than I do (I suppose I could try pretending I have light bones)!
If you’ve got a science question that you’d like Dr. Siobhan Kehoe to answer, feel free to ask below in the comments or on Facebook or Twitter.