The 4 Fundamental Forces

What is a force?

• A push or a pull.

• If something is not moving, a push or pull could start it moving.

• If something is moving, a push or pull could stop it.

YAWN!!!

• If everything stayed the same, we would be BORED.

• For things to change, something’s got to move.

• For something to move, it needs a force.

Forces vs FORCES!!!!• Lots of little forces are happening all the time:

you flick away a piece of dust, you kick a soccer ball, you pull down a curtain, you stop a speeding bullet with your teeth….

• Each of these forces causes something to move or to stop moving.

• These are real forces, but the universe is controlled by some FORCES that are even BIGGER.

The Four Fundamental Forces

• From what we know about the universe, all movements of matter (stuff) are caused by just four forces.

• These forces were created during the first seconds after the Big Bang created the universe.

• They make everything ‘work.’

1. Gravity

• Right now, you’re being pulled down by Gravity.

• We feel gravity almost all the time (not in outer space, but it is still there), but it is most obvious when stuff falls down.

Aristotle’s Error

• Aristotle was a brilliant philosopher who lived several thousand years ago.

• He believed that heavy things fall faster than light things.

• He dropped a rock and a feather, and the rock landed first.

• BUT the items were not shaped the same.

Drop a piece of paper and a ball at the same time. What happened?

•Now crumple the paper into the same shape as the ball and drop again.

•What happened?

Galileo Disproves Aristotle

• Galileo – all objects fall at the same

rate of speed, no matter how big or small they are.

– Legend: he dropped one metal ball and one wood ball off the Leaning Tower of Pisa.

They landed at the same time.

To the Moon!• Astronauts tried

Galileo’s experiment:– dropping a hammer

and a feather.– They landed at the

same time.– With no air resistance

to slow down the wide, flat feather, only gravity was at work.

• Galileo was right.

• Galileo had realized that gravity makes things fall toward the center of the Earth.

• He also figured out that the Earth’s gravity holds the Moon in orbit around it.

• Then he realized that the Sun has gravity, and it holds the planets in orbit around it.

• Based on Galileo’s work, Isaac Newton was able to tease out the exact rules of gravity.

Newton’s Laws of Gravity• All matter has gravity• Gravity pulls masses

together• The more mass, the

more gravity• The farther away, the

less gravity

GRAVITY IS A FUNDAMENTAL FORCE

• Nobody knows why matter has gravity, but we do know exactly how it behaves. – Maybe the graviton?

• It appears to behave the same everywhere in the Universe.

• Therefore, it is a Fundamental Force.

So, the next question is….

• HOW COME WE DON’T GET PULLED TO THE CENTER OF THE EARTH BY GRAVITY????

2. Electromagnetism

• What familiar words make up ‘Electromagnetism?’

Electro + Magnet

• Positive charges are attracted to negative charges.

• Like charges (+ and + or – and --) push each other apart.

Fe = Ke(q1q2) / r2

This should look familiar…

•Fe is the electric force between the charges

•Ke is Coulomb's constant

•q1 is the first charge and q2 is the second charge

•r is the distance between the centers of the charges

EM is in anything that has a charge

• Electrons & Protons• Ions• Parts of Molecules• Electric currents• Magnets

• The ink sticking to your notebook paper• The paint sticking to the wall• Car batteries

EM also lets us ‘feel’ solids, liquids, and gases….

• Atoms are almost all empty space. • But they have shells of negatively-charged electrons,

and those electrons in your hand repel the electrons in your pen.

• The electrons in solids are close together.– Lots of them are touching the

electrons in your ‘solid’ fingers.

• The pen feels ‘solid.’

So about that falling thing….

• We don’t get sucked to the hot molten core of the earth every time we jump up and down because EM stops you.

• Those electrons are repelling each other

• The ground is repelling you…

EM>>Gravity

• Magnets lifting cars• Magnets separating “dark” sand

ELECTROMAGNETISM is a Fundamental Force

• EM is a STRONGER Fundamental Force than gravity – EM is 1037 x stronger

than gravity

Wait a sec….• Inside the middle of

every atom is a hunk of protons.

• They all have positive charges.

• If like charges (+/+ or -/-) repel each other, then how come the protons don’t explode out of the nucleus???

3. Strong Nuclear Force

• The protons don’t repel each other because the Strong Nuclear Force holds them together.

Strong Nuclear Force >> EM

• The strong force is a Fundamental Force:– Generated by GLUONS acting on Quarks– 100x stronger than the EM force. – Only acts on the nucleus ~ 10-15 meters– Without it, there would be no atoms, no

elements, nothing. – The universe would be a big cloud of bumping

particles.

There would be no us….

4. Weak Atomic Force

• Why aren’t electrons sucked into the nucleus of the atom?

• The Weak Force – Beta Emission: no p+ + e- Radioactivity– Radiometric dating– nuclear power and atom bombs

The Nuclear Weak Force

• Shortest range 1000 x shorter than the Strong Force– Lies within the diameter of the nucleus– Causes an instability of the nuclei

• Really Weak 106 x weaker than the Strong Force– 1033 x stronger than gravity

The 4 Fundamental Forces•In order of Strength

- Strong- Electromagnetic- Weak- Gravity

•In order of Distance- EM & Gravity- Strong 10-15 m- Weak 10-18 m

So how do these 4 FORCES fit together?

• The Scotsman Michael Faraday – Watched lightning storms – figured out how electricity and magnetism went

together

• Quantum Mechanics EM, Strong and Weak & the realm of the very Small– Interactions between Quarks, Gluons, and Leptons

• But what of Gravity?

Grand Unified Theory (GUT)

• Einstein’s General Theory of Relativity Gravity & the very Large

• Einstein spent the remaining 30 years of his life trying to figure out how ALL the forces fit together.

• He failed.

String Theory

• Is the closest thing we have to GUT

• Higgs-Boson Particle