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Gravitational & Electric Forces: Similarities & Differences

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  • 0:04 Gravitational Forces
  • 1:49 Electric Forces
  • 2:47 Differences Between…
  • 4:16 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Gravitational and electric forces are two of the four fundamental forces of the universe. They are calculated in very similar ways, but there are some crucial differences between them. In this lesson, learn about these similarities and differences.

Gravitational Forces

When you hold up a ball and let it go, you know it will fall to the ground. You can also look up in the sky at night and see the moon pass overhead. A long time ago, a scientist named Isaac Newton wondered what was making both of these things happen, and he determined that the exact same force that makes the ball fall also keeps the moon in orbit around the Earth. He called this force gravity, and he showed that it's not only the Earth that creates gravitational forces. In fact, all objects with mass exert gravitational forces on each other. That means everything that has mass (including you) exerts a gravitational force on every other object with mass.

If you are exerting gravitational forces on all the other objects with mass that are around you, why can't you feel these forces or see their effects? It turns out that, compared to the other fundamental forces, which include the electromagnetic force and strong and weak nuclear forces, gravity is a very weak force. It only seems so big to us because the Earth is really, really big. It takes a very massive object to create a large enough gravitational force for you to easily detect.

Newton determined that the gravitational force exerted between any two objects with mass is directly proportional to the mass of the two objects and inversely proportional to the square of the distance between them. He called this relationship the Law of Universal Gravitation.


Law of Universal Gravitation


In this above, G is known as the universal gravitation constant. Did you notice that it's a very small number? That is an indication of how weak the force of gravity really is.

Electric Forces

Another very important force is the electric force. If you've ever reached out to touch a metal doorknob or car door and gotten a shock as electricity jumped from you to the metal, then you have experienced one manifestation of the electric force.

Electric forces, like gravitational forces, are one of the four fundamental forces of the universe, and because of this, they have many similarities. Just like objects that have mass exert gravitational forces on each other, objects that are charged will also exert electric forces on each other.

The electric force is directly proportional to the charge of the two objects and inversely proportional to the distance between them squared. Sound familiar? It should! This relationship, known as Coulomb's Law, is very similar to Newton's Law of Universal Gravitation.


Coulombs Law


As you can see, the electrostatic constant, k, is much, much bigger than the universal gravitation constant, G.

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