The Four Fundamental Forces of Nature

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  • 0:01 Fundamental Forces
  • 0:42 Gravitational Force
  • 2:02 Electromagnetic Force
  • 3:31 Strong Force
  • 4:54 Weak Force
  • 6:06 Lesson Summary
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Lesson Transcript
Instructor: Damien Howard

Damien has a master's degree in physics and has taught physics lab to college students.

In this lesson, we'll learn about the four fundamental forces of nature. We will define them and then describe some of the surprising ways in which they affect the world around us every day.

Fundamental Forces

We regularly deal with natural forces in our daily life without ever thinking about it. It's a force that causes water to run downhill and a force that keeps magnets stuck to your refrigerator. All forces can be broken down into at least one of four different types. We call the four most basic forces that all others can be broken down into the four fundamental forces of nature. These four forces consist of the gravitational force, electromagnetic force, strong force, and weak force. In this lesson, we'll go over these four forces, and we will see how they affect the world around us.

Gravitational Force

When you think of gravity you're probably used to thinking on a large scale. You know the Sun's gravity is what keeps planets rotating around it, and it's Earth's gravity that keeps you stuck on the planet's surface. It seems obvious that these huge, galactic-scale objects have gravity associated with them, but what about small things? Does a marble have a gravitational force associated with it?

You might think, ''Of course it does. The marble falls to the ground when I drop it.'' That's gravity at work. Well it is, but it's not the gravitational force given off by the marble. That's the gravitational force given off by the earth. The question is, does the marble exert its own gravitational force on the earth? Does the marble try to attract the earth towards it? The answer is yes.

Gravitational force is the attractive force between all objects with mass. So even a marble exerts its own gravitational force; however, gravitational force is an extremely feeble force. It is the weakest of the four fundamental forces. So it takes an astronomically huge object for us to start noticing gravity's effects with our bare eyes. The marble's gravitational force is so feeble that you'll never see anything attracted towards it.

Electromagnetic Force

Another fundamental force you might be familiar with is electromagnetic force. It's the second strongest of the four fundamental forces, and tells us that there always exists a force between objects with electric charge. You can see this force yourself by holding two bar magnets together. If you hold the two north or south ends together, you'll feel the magnets repelling, and if you hold a north to a south end, you'll feel the magnets attracting. One end of the bar magnet is positively charged, and the other is negatively charged. The opposite charges attract and like ones repel.

You experience electromagnetic force all over the place without realizing it thanks to negatively charged electrons. All matter is made up of atoms, and atoms consist of a nucleus surrounded by an electron cloud. Whenever objects come into contact with each other, what is actually happening is that the electrons in one object repel the electrons in the other. This means the atoms never actually touch. Even magnets that are attracting each other only get so close before the electrons in their atoms repel them enough to stop them from touching.

Right now the atoms in your body aren't actually touching the atoms in the chair you're sitting on. This principle extends to all contact forces as well. When, for example, you kick a ball or push a grocery cart the force you create is made possible thanks to the electromagnetic force between the electrons in you and that object.

Strong Force

Unlike the gravitational and electromagnetic forces, the strong force doesn't come with an obvious example of it in action. This is due to the range over which the force is active. While gravitational and electromagnetic forces have infinite range, the strong force only works over a range of 10-15 meters. So only incredibly tiny objects experience any noticeable effect from the strong force.

To understand what the strong force does we need to look at the nucleus of an atom. A nucleus consists of a collection of positively charged protons and uncharged neutrons. From the electromagnetic force we know that like charges repel. Since there is no negative charge in a nucleus, shouldn't the positively charged protons repel and break up the nucleus?

The strong force is the force that holds together the nucleus of the atom. It is also the force that brings the smallest known particles, quarks, together to form neutrons and protons in the first place. Without the strong force the atomic elements wouldn't be able to form. This would mean no living animals, plants, or even stars would ever exist. The strong force is aptly named as it is the strongest of all the forces at this small scale. It overpowers the electromagnetic force trying to pull the nucleus apart and keeps it together.

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