# Diffraction of Light

What is light? It seems like a simple question, but many people struggle to answer it. That’s okay! The famous Albert Einstein received the Nobel prize for his work in answering that exact question. As you might expect, the answer isn’t all that simple.

Light is a part of the electromagnetic spectrum, which is made up of electromagnetic waves. As the name suggests, this means that light is made up of small changes in electric and magnetic fields, like this!

These electromagnetic waves can carry drastically varied amounts of energy. In fact, when you look at different colors, your eye is separating out the energies for you. The only difference between red and blue light is the energy of the light! To understand color as energy, let’s look at one of the most revealing properties of an electromagnetic wave: its wavelength.

The energy of the wave depends on this factor alone. The longer the distance between the wave crests, the lower the energy of the waves. The closer together they are, the higher the energy. Across the electromagnetic spectrum, wavelengths vary tremendously, from low energy radio waves the length of a school bus to high energy gamma rays even shorter than an atom! There is nothing particularly special about visible light. It’s just another electromagnetic wave. One wavelength of visible light is about half the size of a small bacteria. That just happens to be what human eyes can detect!

The image above shows different kinds of electromagnetic waves and their wavelengths. In gray, you can see how much of each kind of wave is blocked by the atmosphere.

Diffraction gratings are a great way to separate wavelengths. When used to filter white light, the diffraction grating splits up the different energies into a rainbow! When applied to various gases in the video, it shows a unique pattern of light for each one. Since each element produces a different pattern of light, scientists can determine what something is made of just by looking at the spectrum from that object!

This is how scientists know what the sun is made out of. It would be difficult to go retrieve a sample from the surface of the sun for fairly obvious reasons. Similarly, astronomers have been able to use this knowledge to find out what makes up other stars, galaxies, nebulae, and even other planets! Every bit of knowledge that we have about everything outside of our solar system comes directly from observing and analyzing light.

# From Apples to Inertia

One day, Isaac Newton was sitting underneath a tree, and an apple falls and bonks him on the head. In a stroke of genius and coincidence, Isaac comes up with the theory of gravity and the rest is history…or so the story goes. This simple anecdote actually does a disservice to just how much of a contribution Isaac Newton made to the core of science. While there are many subjects to pick from, today, we are going to focus on the first of Newton’s Three Laws of Motion.

As many of us learned from another famous scientist, Bill Nye, inertia is a property of matter. This is also Newton’s First Law of Motion, and it is actually a very simple concept: an object at rest or in motion will remain at rest or in motion unless acted upon unless something makes it move or stop. So why did it take someone like Isaac Newton–the guy who invented Calculus just to help him understand gravity–to come up with it for us?

The main reason is that in our experience, the law seems wrong. If you throw a ball, it doesn’t keep going forever. It hits the ground and stops rolling after a bit. If you start walking, you don’t just glide on forever. This does not break Newton’s first law though, and that is because there are little forces like the air and the friction of rolling a ball that slow them down. These outside forces are exactly what the law is talking about! If instead you were to throw a ball out in space, it would keep on going forever until it hit something or got pulled in by gravity!

In these demonstrations, we are showing that an object at rest remains at rest. The little metal hex nuts sitting on top of the orange ring are stationary directly above the small opening of the bottle. When the ring is pulled out, the hex nuts do not move horizontally, and instead fall straight down due to gravity!

This idea can be expanded to the table cloth magic trick that you may have seen, but  you have to get it just right!

# Bernoulli’s Principle Will Leave You Breathless!

What sorcery is this!? Science it turns out! This is a great example of Bernoulli’s Principle! In short, this states that moving air has a lower pressure. Imagine trying to dig a hole in a pool of water: as soon as some of the water gets moved out of the way, the surrounding water rushes in to take its place. Air does the same thing: whenever it moves, the lower pressure draws air in around it!

The cup and straw demonstration shows this nicely, and it’s also a great experiment to try at home! By taking each apparatus and blowing into it, we can see there is a pretty huge difference.

Inside the cup, air is moving quickly. This causes a lower pressure inside the cup than outside, and air that tries to fill up the space suctions the balloon in place. Alternatively, the cup with holes in the sides allows the surrounding air to help out. Very similar to the Bernoulli Bag, nearby air joins in creating a larger column of air that can lift, and even suspend, the balloon.

We know this looks like a trick, because it’s hard to tell from watching that he is exhaling vigorously in both cases. If you don’t believe us, definitely try it yourself!  Of course, it is possible to hold the balloon into the cup by inhaling, but it’s actually more difficult to suck up the balloon from a short distance away! The difference in pressure from blowing fast moving air into the cup is more effective at sucking up the balloon.

While Bernoulli’s Principle can be tricky to understand, it is very important! The fact that fast moving air has a lower pressure is one of the primary ways that airplanes are able to generate lift! The air going over the wing actually goes faster than the air below, which you can see in this very cool shot from a wind tunnel!

Credit: Holger Babinsky, University of Cambridge

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