FUNDAMENTAL FORCES OF NATURE - A force is defined as a push or pull that changes an object's state of motion or causes the object to deform. Newton defined a force as anything that caused an object to accelerate. The force of gravity pulls you down into your seat, toward the Earth's center. You feel it as your weight. Why don't you fall through your seat? Well, another force, electromagnetism, holds the atoms of your seat together, preventing your atoms from intruding on those of your seat. Electromagnetic interactions in your computer monitor are also responsible for generating light that allows you to read the screen. Gravity and electromagnetism are just two of the four fundamental forces of nature, specifically two that you can observe every day. The remaining two forces work at the atomic level, which we never feel, despite being made of atoms. The strong force holds the nucleus together. Lastly, the weak force is responsible for radioactive decay, specifically, beta decay where a neutron within the nucleus changes into a proton and an electron, which is ejected from the nucleus. Without these fundamental forces, you and all the other matter in the universe would fall apart and float away. The first force that you ever became aware of was probably gravity. Gravity holds the moon, planets, sun, stars and galaxies together in the universe in their respective orbits. It can work over immense distances and has an infinite range. Isaac Newton envisioned gravity as a pull between any two objects that was directly related to their masses and inversely related to the square of the distance separating them.

 

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Fundamental Forces Of Nature

What are the four fundamental forces of nature?

BY CRAIG FREUDENRICH, PH.D.

 

As you sit in front of your computer reading this article, you may be unaware of the many forces acting upon you.

A force is defined as a push or pull that changes an object's state of motion or causes the object to deform.

Newton defined a force as anything that caused an object to accelerate -- F = ma, where F is force, m is mass and a is acceleration.

The familiar force of gravity pulls you down into your seat, toward the Earth's center. You feel it as your weight.

Why don't you fall through your seat? Well, another force, electromagnetism, holds the atoms of your seat together, preventing your atoms from intruding on those of your seat.

Electromagnetic interactions in your computer monitor are also responsible for generating light that allows you to read the screen.

Gravity and electromagnetism are just two of the four fundamental forces of nature, specifically two that you can observe every day.

What are the other two, and how do they affect you if you can't see them?

The remaining two forces work at the atomic level, which we never feel, despite being made of atoms. The strong force holds the nucleus together.

Lastly, the weak force is responsible for radioactive decay, specifically, beta decay where a neutron within the nucleus changes into a proton and an electron, which is ejected from the nucleus.

Without these fundamental forces, you and all the other matter in the universe would fall apart and float away.

Let's look at each fundamental force, what each does, how it was discovered and how it relates to the others.

Gravity Getting You Down?

 The first force that you ever became aware of was probably gravity.

As a toddler, you had to learn to rise up against it and walk. When you stumbled, you immediately felt gravity bring you back down to the floor.

Besides giving toddlers trouble, gravity holds the moon, planets, sun, stars and galaxies together in the universe in their respective orbits.

It can work over immense distances and has an infinite range.

Isaac Newton envisioned gravity as a pull between any two objects that was directly related to their masses and inversely related to the square of the distance separating them.

His law of gravitation enabled mankind to send astronauts to the moon and robotic probes to the outer reaches of our solar system.

From 1687 until the early 20th century, Newton's idea of gravity as a "tug-of-war" between any two objects dominated physics.

But one phenomenon that Newton's theories couldn't explain was the peculiar orbit of Mercury. The orbit itself appeared to rotate (also known as precession).

This observation frustrated astronomers since the mid-1800s.

In 1915, Albert Einstein realized that Newton's laws of motion and gravity didn't apply to objects in high gravity or at high speeds, like the speed of light.

In his general theory of relativity, Albert Einstein envisioned gravity as a distortion of space caused by mass.

Imagine that you place a bowling ball in the middle of a rubber sheet. The ball makes a depression in the sheet (a gravity well or gravity field).

If you roll a marble toward the ball, it will fall into the depression (be attracted to the ball) and may even circle the ball (orbit) before it hits.

Depending upon the speed of the marble, it may escape the depression and pass the ball, but the depression might alter the marble's path.

Gravity fields around massive objects like the sun do the same.

Einstein derived Newton's law of gravity from his own theory of relativity and showed that Newton's ideas were a special case of relativity, specifically one applying to weak gravity and low speeds.

When considering massive objects (Earth, stars, galaxies), gravity appears to be the most powerful force.

However, when you apply gravity to the atomic level, it has little effect because the masses of subatomic particles are so small.

On this level, it's actually downgraded to the weakest force.

Let's look at electromagnetism, the next fundamental force.

Keeping It Together with Electromagnetism

If you brush your hair several times, your hair may stand on end and be attracted to the brush. Why?

The movement of the brush imparts electrical charges to each hair and the identically charged individual hairs repel each other.

Similarly, if you place identical poles of two bar magnets together, they will repel each other.

But set the opposite poles of the magnets near one another, and the magnets will attract each other.

These are familiar examples of electromagnetic force; opposite charges attract, while like charges repel.

Scientists have studied electromagnetism since the 18th century, with several making notable contributions.

In 1785, famed French physicist Charles Coulomb described the force of electrically charged objects as directly proportional to the magnitudes of the charges and inversely related to the square of the distances between them.

Like gravity, electromagnetism has an infinite range.

In 1819, Danish physicist Hans Christian Oersted discovered that electricity and magnetism were very much related, leading him to declare that an electric current generates a magnetic force.

British-born physicist and chemist Michael Faraday weighed in on electromagnetism, showing that magnetism could be used to generate electricity in 1839.

In the 1860s, James Clerk Maxwell, the Scottish math and physics whiz, derived equations that described how electricity and magnetism were related.

Finally, Dutchman Hendrik Lorentz calculated the force acting on a charged particle in an electromagnetic field in 1892.

When scientists worked out the structure of the atom in the early 20th century, they learned that subatomic particles exerted electromagnetic forces on each other.

For example, positively charged protons could hold negatively charged electrons in orbit around the nucleus.

Furthermore, electrons of one atom attracted protons of neighboring atoms to form a residual electromagnetic force, which prevents you from falling through your chair.

But how does electromagnetism work at an infinite range in the large world and a short range at the atomic level?

Physicists thought that photons transmitted electromagnetic force over large distances.

But they had to devise theories to reconcile electromagnetism at the atomic level, and this led to the field of quantum electrodynamics (QED).

According to QED, photons transmit electromagnetic force both macroscopically and microscopically; however, subatomic particles constantly exchange virtual photons during their electromagnetic interactions.

But electromagnetism can't explain how the nucleus holds together. That's where nuclear forces come into play.

May the Nuclear Forces Be with You

The nucleus of any atom is made of positively charged protons and neutral neutrons. Electromagnetism tells us that protons should repel each other and the nucleus should fly apart.

We also know that gravity doesn't play a role on a subatomic scale, so some other force must exist within the nucleus that is stronger than gravity and electromagnetism.

In addition, since we don't perceive this force every day as we do with gravity and electromagnetism, then it must operate over very short distances, say, on the scale of the atom.

The force holding the nucleus together is called the strong force, alternately called the strong nuclear force or strong nuclear interaction.

In 1935, Hideki Yukawa modeled this force and proposed that protons interacting with each other and with neutrons exchanged a particle called a meson -- later called a pion -- to transmit the strong force.

In the 1950s, physicists built particle accelerators to explore the structure of the nucleus.

When they crashed atoms together at high speeds, they found the pions predicted by Yukawa.

They also found that protons and neutrons were made of smaller particles called quarks. So, the strong force held the quarks together, which in turn held the nucleus together.

One other nuclear phenomenon had to be explained: radioactive decay.

In beta emission, a neutron decays into a proton, anti-neutrino and electron (beta particle).

The electron and anti-neutrino are ejected from the nucleus.

The force responsible for this decay and emission must be different and weaker than the strong force, thus it's unfortunate name -- the weak force or the weak nuclear force or weak nuclear interaction.

With the discovery of quarks, the weak force was shown to be responsible for changing one type of quark into another through the exchange of particles called W and Z bosons, which were discovered in 1983.

Ultimately, the weak force makes nuclear fusion in the sun and stars possible because it allows the hydrogen isotope deuterium to fom and fuse.

Now that you can name the four forces -- gravity, electromagnetism, the weak force and the strong force -- we'll see how they compare and interact with one another.

Comparing the Fundamental Forces

From the fields of QED and quantum chromodynamics, or QCD, the field of physics that describes the interactions between subatomic particles and nuclear forces, we see that many of the forces are transmitted by objects exchanging particles called gauge particles or gauge bosons.

These objects can be quarks, protons, electrons, atoms, magnets or even planets.

So, how does exchanging particles transmit a force? Consider two ice skaters standing at some distance apart.

If one skater throws a ball to the other, the skaters will move farther away from each other. Forces work in a similar way.

Physicists have isolated the gauge particles for most of the forces. The strong force uses pions and another particle called a gluon.

The weak force uses W and Z bosons. The electromagnetic force uses photons.

Gravity is thought to be conveyed by a particle called a graviton; however, gravitons haven't been found yet.

Some of the gauge particles associated with the nuclear forces have mass, while others don't (electromagnetism, gravity).

Because electromagnetic force and gravity can operate over huge distances like light-years, their gauge particles must be able to travel at the speed of light, perhaps even faster for gravitons.

Physicists don't know how gravity is transmitted.

But according to Einstein's theory of special relativity, no object with mass can travel at the speed of light, so it makes sense that photons and gravitons are mass-less gauge particles.

In fact, physicists have firmly established that photons have no mass.

Which force is the mightiest of them all? That would be the strong nuclear force.

However, it acts only over a short range, approximately the size of a nucleus.

The weak nuclear force is one-millionth as strong as the strong nuclear force and has an even shorter range, less than a proton's diameter.

The electromagnetic force is about 0.7 percent as strong as the strong nuclear force, but has an infinite range because photons carrying the electromagnetic force travel at the speed of light.

Finally, gravity is the weakest force at about 6 x 10-29 times that of the strong nuclear force. Gravity, however, has an infinite range. 

Physicists are currently pursuing the ideas that the four fundamental forces may be related and that they sprang from one force early in the universe.

The idea isn't unprecedented. We once thought of electricity and magnetism as separate entities, but the work of Oersted, Faraday, Maxwell and others showed that they were related.

Theories that relate the fundamental forces and subatomic particles are called fittingly grand unified theories. More on them next.

Uniting the Fundamental Forces

Science never rests, so the work on fundamental forces is far from finished.

The next challenge is to construct one grand unified theory of the four forces, an especially difficult task since scientists have struggled to reconcile theories of gravity with those of quantum mechanics.

That's where particle accelerators, which can induce collisions at higher energies, come in handy.

In 1963, physicists Sheldon Glashow, Abdul Salam and Steve Weinberg suggested that the weak nuclear force and electromagnetic force might combine at higher energies in what would be called the electroweak force.

They predicted that this would occur at an energy of about 100 giga-electron volts (100GeV) or a temperature of 1015 K, which occurred shortly after the Big Bang.

In 1983, physicists reached these temperatures in a particle accelerator and showed that the electromagnetic force and weak nuclear force were related.

Theories predict that the strong force will unite with the electroweak force at energies above 1015 GeV and that all the forces may unite at energies above 1019 GeV.

These energies approach the temperature at the earliest portion of the Big Bang. Physicists are striving to build particle accelerators that might reach these temperatures.

The largest particle accelerator is the Large Hadron Collider at CERN in Geneva, Switzerland.

When it comes online, it will be capable of accelerating protons to 99.99 percent the speed of light and reaching collision energies of 14 tera-electron volts or 14 TeV, which is equal to 14,000 GeV or 1.4 x 104 GeV.

If physicists can show that the four fundamental forces indeed came from one unified force when the universe cooled from the Big Bang, will that change your daily life? Probably not.

However, it will advance our understanding of the nature of forces, as well as the origins and fate of the universe.

Craig Freudenrich, Ph.D., is a freelance science writer. He earned a B.A. in biology from West Virginia University and a Ph.D. in physiology from the University of Pittsburgh School of Medicine. He has over 25 years experience in biomedical research, science education, and science writing.

https://science.howstuffworks.com/environmental/earth/geophysics/fundamental-forces-of-nature.htm

 

The wild-haired brilliant guy behind the first force we're going to talk about

This little guy is about to find out what gravity is all about. 

C'mon, everyone knows that opposites attract, even Paula Abdul.

Dr. Hideki Yukawa, right, receives the Nobel Prize for physics in Stockholm from then Crown Prince Gustaf Adolf of Sweden Dec. 10, 1949, for his postulation on the meson.

The magnet core of the Large Hadron Collider might one day unite the strong force with the electroweak force.

NEWTON'S LAWS OF MOTION - Sir Isaac Newton was a British physicist who, in many respects, can be viewed as the greatest physicist of all time. Though there were some predecessors of note, such as Archimedes, Copernicus, and Galileo, it was Newton who truly exemplified the method of scientific inquiry that would be adopted throughout the ages. For nearly a century, Aristotle's description of the physical universe had proven to be inadequate to describe the nature of movement. Newton tackled the problem and came up with three general rules about the movement of objects which have been dubbed as "Newton's three laws of motion." Newton's First Law of Motion states that in order for the motion of an object to change, a force must act upon it. This is a concept generally called inertia. Newton's Second Law of Motion defines the relationship between acceleration, force, and mass. Newton's Third Law of Motion states that any time a force acts from one object to another, there is an equal force acting back on the original object. If you pull on a rope, therefore, the rope is pulling back on you as well. Free body diagrams are the means by which you can track the different forces acting on an object and, therefore, determine the final acceleration. Vector mathematics is used to keep track of the directions and magnitudes of the forces and accelerations involved.

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Newton's Laws of Motion

Introduction to Newton's Laws of Motion

By Andrew Zimmerman Jones

Each law of motion Newton developed has significant mathematical and physical interpretations that are needed to understand motion in our universe.

The applications of these laws of motion are truly limitless.

Essentially, Newton's laws define the means by which motion changes, specifically the way in which those changes in motion are related to force and mass.

Origins and Purpose of Newton's Laws of Motion

Sir Isaac Newton (1642-1727) was a British physicist who, in many respects, can be viewed as the greatest physicist of all time.

Though there were some predecessors of note, such as Archimedes, Copernicus, and Galileo, it was Newton who truly exemplified the method of scientific inquiry that would be adopted throughout the ages.

For nearly a century, Aristotle's description of the physical universe had proven to be inadequate to describe the nature of movement (or the movement of nature, if you will).

Newton tackled the problem and came up with three general rules about the movement of objects which have been dubbed as "Newton's three laws of motion."

In 1687, Newton introduced the three laws in his book "Philosophiae Naturalis Principia Mathematica" (Mathematical Principles of Natural Philosophy), which is generally referred to as the "Principia."

This is where he also introduced his theory of universal gravitation, thus laying the entire foundation of classical mechanics in one volume.

Newton's Three Laws of Motion

·      Newton's First Law of Motion states that in order for the motion of an object to change, a force must act upon it. This is a concept generally called inertia.

·      Newton's Second Law of Motion defines the relationship between acceleration, force, and ​mass.

·      Newton's Third Law of Motion states that any time a force acts from one object to another, there is an equal force acting back on the original object. If you pull on a rope, therefore, the rope is pulling back on you as well.

Working With Newton's Laws of Motion

·      Free body diagrams are the means by which you can track the different forces acting on an object and, therefore, determine the final acceleration.

·      Vector mathematics is used to keep track of the directions and magnitudes of the forces and accelerations involved.

·      Variable equations are used in complex physics problems.

Newton's First Law of Motion

Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it. - Newton's First  Law of Motion, translated from the "Principia"

This is sometimes called the Law of Inertia, or just inertia. Essentially, it makes the following two points:

·      An object that is not moving will not move until a force acts upon it.

·      An object that is in motion will not change velocity (or stop) until a force acts upon it.

The first point seems relatively obvious to most people, but the second may take some thinking through.

Everyone knows that things don't keep moving forever. If I slide a hockey puck along a table, it slows and eventually comes to a stop.

But according to Newton's laws, this is because a force is acting on the hockey puck and, sure enough, there is a frictional force between the table and the puck.

That frictional force is in the direction that is opposite the movement of the puck. It's this force which causes the object to slow to a stop.

In the absence (or virtual absence) of such a force, as on an air hockey table or ice rink, the puck's motion isn't as hindered.

Here is another way of stating Newton's First Law:

A body that is acted on by no net force moves at a constant velocity (which may be zero) and zero acceleration.

So, with no net force, the object just keeps doing what it is doing.

It is important to note the words net force. This means the total forces upon the object must add up to zero.

An object sitting on my floor has a gravitational force pulling it downward, but there is also a normal force pushing upward from the floor, so the net force is zero. Therefore, it doesn’t move.

To return to the hockey puck example, consider two people hitting the hockey puck on exactly opposite sides at exactly the same time and with exactly identical force. In this rare case, the puck would not move.

Since both velocity and force are vector quantities, the directions are important to this process.

If a force (such as gravity) acts downward on an object and there's no upward force, the object will gain a vertical acceleration downward. The horizontal velocity will not change, however.

If I throw a ball off my balcony at a horizontal speed of 3 meters per second, it will hit the ground with a horizontal speed of 3 m/s (ignoring the force of air resistance), even though gravity exerted a force (and therefore acceleration) in the vertical direction. 

If it weren't for gravity, the ball would have kept going in a straight line... at least, until it hit my neighbor's house.

Newton's Second Law of Motion

The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body. - (Translated from the "Princip​ia")

The mathematical formulation of the second law is shown below, with F representing the force, m representing the object's mass and a representing the object's acceleration.

∑​ F = ma

This formula is extremely useful in classical mechanics, as it provides a means of translating directly between the acceleration and force acting upon a given mass.

A large portion of classical mechanics ultimately breaks down to applying this formula in different contexts.

The sigma symbol to the left of the force indicates that it is the net force, or the sum of all the forces.

As vector quantities, the direction of the net force will also be in the same direction as the acceleration. 

You can also break the equation down into x and y (and even z) coordinates, which can make many elaborate problems more manageable, especially if you orient your coordinate system properly.

You'll note that when the net forces on an object sum up to zero, we achieve the state defined in Newton's First Law: the net acceleration must be zero.

We know this because all objects have mass (in classical mechanics, at least).

If the object is already moving, it will continue to move at a constant velocity, but that velocity will not change until a net force is introduced.

Obviously, an object at rest will not move at all without a net force.

The Second Law in Action

A box with a mass of 40 kg sits at rest on a frictionless tile floor. With your foot, you apply a 20 N force in a horizontal direction. What is the acceleration of the box?

The object is at rest, so there is no net force except for the force your foot is applying. Friction is eliminated.

Also, there's only one direction of force to worry about. So, this problem is very straightforward.

You begin the problem by defining your coordinate system. The mathematics is similarly straightforward:

F =  m *  a

F / m = ​a

20 N / 40 kg = a = 0.5 m / s2

The problems based on this law are literally endless, using the formula to determine any of the three values when you are given the other two.

As systems become more complex, you will learn to apply frictional forces, gravity, electromagnetic forces, and other applicable forces to the same basic formulas.

Newton's Third Law of Motion

To every action there is always opposed an equal reaction; or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. - (Translated from the ​​"Principia")

We represent the Third Law by looking at two bodies, A and B, that are interacting.

We define FA as the force applied to body A by body B, and FA as the force applied to body B by body A.

These forces will be equal in magnitude and opposite in direction. In mathematical terms, it is expressed as:

FB = - FA

or

FA + FB = 0

This is not the same thing as having a net force of zero, however.

If you apply a force to an empty shoebox sitting on a table, the shoebox applies an equal force back on you.

This doesn't sound right at first — you're obviously pushing on the box, and it is obviously not pushing on you.

Remember that according to the Second Law, force and acceleration are related but they aren't identical!

Because your mass is much larger than the mass of the shoebox, the force you exert causes it to accelerate away from you. The force it exerts on you wouldn't cause much acceleration at all.

Not only that, but while it's pushing on the tip of your finger, your finger, in turn, pushes back into your body, and the rest of your body pushes back against the finger, and your body pushes on the chair or floor (or both), all of which keeps your body from moving and allows you to keep your finger moving to continue the force.

There's nothing pushing back on the shoebox to stop it from moving.

If, however, the shoebox is sitting next to a wall and you push it toward the wall, the shoebox will push on the wall and the wall will push back.

The shoebox will, at this point, stop moving. You can try to push it harder, but the box will break before it goes through the wall because it isn't strong enough to handle that much force.

Newton's Laws in Action

Most people have played tug of war at some point.

A person or group of people grab the ends of a rope and try to pull against the person or group at the other end, usually past some marker (sometimes into a mud pit in really fun versions), thus proving that one of the groups is stronger than the other.

All three of Newton's Laws can be seen in a tug of war.

There frequently comes a point in a tug of war when neither side is moving. Both sides are pulling with the same force.

Therefore, the rope does not accelerate in either direction. This is a classic example of Newton's First Law.

Once a net force is applied, such as when one group begins pulling a bit harder than the other, an acceleration begins. This follows the Second Law.

The group losing ground must then try to exert more force. When the net force begins going in their direction, the acceleration is in their direction.

The movement of the rope slows down until it stops and, if they maintain a higher net force, it begins moving back in their direction.

The Third Law is less visible, but it's still present.

When you pull on the rope, you can feel that the rope is also pulling on you, trying to move you toward the other end.

You plant your feet firmly in the ground, and the ground actually pushes back on you, helping you to resist the pull of the rope.

Next time you play or watch a game of tug of war — or any sport, for that matter — think about all the forces and accelerations at work.

It's truly impressive to realize that you can understand the physical laws that are in action during your favorite sport.

Andrew Zimmerman Jones.

Math and Physics Expert

Education

M.S., Mathematics Education, Indiana University

B.A., Physics, Wabash College

Introduction

Academic researcher, educator, and writer with 23 years of experience in physical sciences

Works at Indiana Department of Education as senior assessment specialist in mathematics

Co-author of String Theory For Dummies

Member of the National Association of Science Writers

Experience

Andrew Zimmerman Jones is a former writer for ThoughtCo who contributed nearly 200 articles for more than 10 years. His topics ranged from the definition of energy to vector mathematics. Andrew is a dedicated educator; and he uses his background in the physical sciences, educational assessment, writing, and communications to advance that mission. 

Andrew is co-author of String Theory For Dummies, which discusses the basic concepts of this controversial approach. String theory tries to explain certain phenomena that are not currently explainable under the standard quantum physics model. 

Since 2018, Andrew has worked at the Indiana Department of Education as a senior assessment specialist in mathematics; prior to which he served as a senior assessment editor at CTB/McGraw Hill for 10 years. In addition, Andrew was a researcher at Indiana University's Cyclotron Facility. He is a member of the National Association of Science Writers. 

Education

Andrew Zimmerman Jones received an M.S. in Mathematics Education from Indiana University–Purdue and a B.A. in Physics from Wabash College.

Awards and Publications

String Theory For Dummies (Wiley–For Dummies Series, 2009)

Harold Q. Fuller Prize in Physics (Wabash College, 1998)

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https://www.thoughtco.com/introduction-to-newtons-laws-of-motion-2698881