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May the Four Forces Be With You!

May the Four Forces Be With You!

the force be with you? Much to learn you still have, padawan. In our universe
it would be more appropriate to say, “May the four forces be with you.”


are four fundamental forces that bind our universe and its building blocks
together. Two of them are easy to spot — gravity keeps your feet on the ground
while electromagnetism keeps your devices running. The other two are a little
harder to see directly in everyday life, but without them, our universe would
look a lot different!

explore these forces in a little more detail.

Gravity: Bringing the universe


you jump up, gravity brings you back down to Earth. It also keeps the solar
system together … and our galaxy, and our local group of galaxies and our
supercluster of galaxies.

Gravity pulls
everything together. Everything, from the bright centers of the universe to the
planets farthest from them. In fact, you (yes, you!) even exert a gravitational
force on a galaxy far, far away. A tiny gravitational force, but a force


Credit: NASA and the Advanced Visualization Laboratory at the
National Center for Supercomputing and B. O’Shea, M. Norman

its well-known reputation, gravity is actually the weakest of the four forces.
Its strength increases with the mass of the two objects involved. And its range
is infinite, but the strength drops off as the square of the distance. If you
and a friend measured your gravitational tug on each other and then doubled the
distance between you, your new gravitational attraction would just be a quarter
of what it was. So, you have to be really close together, or really big, or
both, to exert a lot of gravity.

so, because its range is infinite, gravity is responsible for the formation of
the largest structures in our universe! Planetary systems, galaxies and clusters of galaxies all formed because gravity
brought them together.

truly surrounds us and binds us together.

Electromagnetism: Lighting the way


know that shock you get on a dry day after shuffling across the carpet? The
electricity that powers your television? The light that illuminates your room
on a dark night? Those are all the work of electromagnetism. As the name
implies, electromagnetism is the force that includes both electricity and

keeps electrons orbiting the nucleus at the center of atoms and allows chemical
compounds to form (you know, the stuff that makes up us and everything around
us). Electromagnetic waves are also known as light. Once started, an
electromagnetic wave will travel at the speed of light until it interacts with
something (like your eye) — so it will be there to light up the dark places.


gravity, electromagnetism works at infinite distances. And, also like gravity,
the electromagnetic force between two objects falls as the square of their
distance. However, unlike gravity, electromagnetism doesn’t just attract.
Whether it attracts or repels depends on the electric charge of the objects
involved. Two negative charges or two positive charges repel each other; one of
each, and they attract each other. Plus. Minus. A balance.

is what happens with common household magnets. If you hold them with the same
“poles” together, they resist each other. On the other hand, if you hold a
magnet with opposite poles together — snap! — they’ll attract each other.

might just explain the relationship between a certain scruffy-looking
nerf-herder and a princess.

Strong Force: Building the building


Credit: Lawrence Livermore National Laboratory

The strong force is where things get really
small. So small, that you can’t see it at work directly. But don’t let your
eyes deceive you. Despite acting only on short distances, the strong force
holds together the building blocks of the atoms, which are, in turn, the
building blocks of everything we see around us.

gravity, the strong force always attracts, but that’s really where their
similarities end. As the name implies, the force is strong with the strong
force. It is the strongest of the four
It brings together protons and neutrons to form the nucleus of atoms — it has
to be stronger than electromagnetism to do it, since all those protons are
positively charged. But not only that, the strong force holds together the
quarks — even tinier particles — to form those very protons and neutrons.

the strong force only works on very, very, very small distances. How small?
About the scale of a medium-sized atom’s nucleus. For those of you who like the
numbers, that’s about 10-15 meters, or 0.000000000000001 meters.
That’s about a hundred billion times smaller than the width of a human hair!

tiny scale is why you don’t directly see the strong force in your day-to-day
life. Judge a force by its physical size, do you? 

Weak Force: Keeping us in sunshine


you thought it was hard to see the strong force, the weak force works on even smaller scales
— 1,000 times smaller. But it, too, is extremely important for life as we know
it. In fact, the weak force plays a key role in keeping our Sun shining.

what does the weak force do? Well … that requires getting a little into the
weeds of particle physics. Here goes nothing! We mentioned quarks earlier —
these are tiny particles that, among other things, make up protons and
neutrons. There are six types of quarks, but the two that make up protons and
neutrons are called up and down quarks. The weak force changes one quark type
into another. This causes neutrons to decay into protons (or the other way
around) while releasing electrons and ghostly particles called neutrinos.

for example, the weak force can turn a down quark in a neutron into an up
quark, which will turn that neutron into a proton. If that neutron is in an
atom’s nucleus, the electric charge of the nucleus changes. That tiny change turns
the atom into a different element! Such reactions are happening all
the time in our Sun, giving it the energy to shine.

weak force might just help to keep you in the (sun)light.


four of these forces run strong in the universe. They flow between all things
and keep our universe in balance. Without them, we’d be doomed. But these
forces will be with you. Always.

can learn more about gravity from NASA’s Space Place and follow NASAUniverse on Twitter or Facebook to learn about some of the cool
cosmic objects we study with light.

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