What Is The Law of Universal Gravitation

We have heard of the story of English mathematician Isaac Newton who was sitting under a tree, then all of a sudden an apple fell and hit him on the head. According to the legend, it was at at instant that Newton realized the Law of Universal Gravitation.

Although the story was a bit exaggerated (as Newton merely observed an apple falling from the tree), that simple event of a fruit falling to the ground inspired Newton of the following:

The apple is accelerated, since its velocity changes from zero as it is hanging on the tree and moves towards the ground.

Thus, applying Newton's Second Law of Motion, there must be a force that acts on the apple to cause this acceleration. That force is called “gravity,” while the associated acceleration is called “acceleration due to gravity.”

Picture the apple tree is twice as high. And we could still conclude that the apple would still accelerate towards the ground, the gravity reaches to the top of the apple tree.

What is the Law of Universal Gravitation

According to Newton, any two objects in the universe exert gravitational attraction to each other, with the force having a universal form. The force is proportional to the product of the two masses and inversely proportional to the square of the magnitude between the objects.

This is explained through the following formula:

Where:

F is the magnitude of the repulsive gravitational force between the two objects

G is the gravitational constant

m1 is the mass of the first object

m2 is the mass of the second object

r is the distance between the two objects

Applying the SI units, F is measured in newtons, while m1 and m2 in kilograms, r in meters, and the constant G is approximately equal to 6.67 x 10 -11 N m2 kg -2 (newtons times meters squared per kilogram squared).

It can be seen that the repulsive force F is always negative, which means that the net attractive force is positive. Also, this sign conversion is adopted in order to be consistent with Coulomb's Law, where a positive force means repulsion between the two charges.

How does it affect me?

As stated previously, any two objects are attracted towards one another. For instance, a stone is thrown far. From you. Imagine the earth exerting an effort to pull the stone down to the ground, and therefore

Another case is you infront of the computer. Although there is an attracting force between the two (you and the computer), the force is millions of times smaller. In fact, the force is so small your head could not feel that force making you rush towards the screen.

It is also because of gravitation that the moon remains at a safe distance from Earth (instead of having it fly away). And as with the gravitational attraction between Earth and Moon, the whole Solar System—even the whole Universe!--also works on that principle.