Understanding Waves

Oliver Bennett

Welcome back to Waves and Nuclear Physics, the show where we try and make year 11 physics just a little bit less, erm, intimidating. I’m Oliver—if this is your first episode, lovely to have you here! Let’s just jump in: what actually is a wave? It sounds so simple, but the definition really underpins everything else in waves topics.

Samantha Davis

Yeah, exactly! So, when we talk about waves, like, we’re talking about disturbances or movements that transfer energy from one place to another without the particles actually moving along. And it happens around us all the time—think about the ripple when you toss a rock in a pond, or, you know, the music you’re hearing right now through your speakers—waves in action!

Ethan Miller

Totally. And, you know, I remember this moment as a kid—I must've been, what, eight? We had this giant thunderstorm, and I’d see the lightning flash before I ever heard the thunder. And I just could not figure it out. But, like, it turns out, that’s because light waves travel way faster than sound waves. That blew my mind. Sound, light, water—waves are, honestly, everywhere in life.

Emily Clarke

It’s so true! And I think sometimes it’s easy to forget that even things like radio waves, or the signals in your mobile, are all waves just doing their thing, carrying energy and information. It’s all about energy moving from point A to B, not the particles themselves making the journey—which is kind of wild, isn’t it?

Emily Clarke

So, let’s get a bit more specific—mechanical waves are a big deal in physics. They’re the waves that actually need a medium, like air or water, to travel through. Sound? That’s a mechanical wave. If there’s no stuff—no medium—no sound.

Oliver Bennett

Exactly, and here’s where physics terms kick in. When you look at a mechanical wave, especially sound, we describe it moving by “compressions” and “rarefactions”. A compression is where the particles are squished together. Rarefaction? That’s where they’re spread out. So, for a sound wave—say, when you shout—those variations in air pressure travel as a series of compressions and rarefactions all the way to your friend’s ear.

Emily Clarke

Yeah, and this reminds me of a classroom demo I used to love. I’d grab a slinky, stretch it out on the table, and push one end in and out. You could see these bunched-up sections moving down the slinky—that's your compressions—and the stretched bits are rarefactions. It’s honestly the easiest way to see how sound travels as a longitudinal wave. Everyone loved the slinky; I think the noise annoyed my colleague though!

Ethan Miller

Haha, who doesn’t love classroom slinky chaos? So, like, I always mix up which is which—longitudinal and transverse—but in this case with sound you see the vibration travelling parallel to the direction of the wave. Compression and rarefaction—the signature of a longitudinal mechanical wave.

Samantha Davis

Right, and it’s neat because water waves actually do the opposite—those are transverse, with vibrations happening up and down while the wave itself zips forward. But yeah, with sound, you get those squish-and-stretch patterns along the direction the wave is moving.

Oliver Bennett

Let’s talk graphs, because seeing the way a wave behaves makes it so much clearer, in my opinion. So, imagine you’re plotting a wave—you have one axis for displacement, which is, how far a particle is from its resting point. And the other is usually time or distance along the wave. Why bother? Because it shows us everything—peaks, dips, and all the action.

Ethan Miller

Yeah, totally. When you get these wiggly lines on graph paper, you’re usually seeing a transverse wave—a classic example is, like, water waves where particles move up and down. Those crests and troughs? That’s the signature look of a transverse wave when graphed. It’s actually pretty cool to see that wavy pattern matched to real water movement.

Oliver Bennett

Right, and contrast that with sound waves, which are longitudinal. If I did a quick sketch, for water, I’d draw a line wiggling up and down. For sound, though? I’d mark out parts where the line is squished closer together (that’s compression), and parts where it’s stretched (rarefaction). It can look confusing, but the axis tells you what you’re looking at—either the displacement of air particles or pressure changes over time. It’s not always a wavy up-and-down; sometimes, it’s patches of bunched and spread-out particles along a line.

Emily Clarke

And I think the key takeaway is, graphs are like a language for waves. If you learn to read them, you can understand what the wave’s doing—whether it’s moving energy up and down, or squishing and stretching. You almost never see a test question without one, right Oliver?

Oliver Bennett

Ha, never! They’re exam favourites for a reason: they tell you loads at a glance, and once you’ve got them down, you can compare different wave types super easily.

Samantha Davis

So, if we look really closely at those graphs—you’ll spot these main features: the crest, which is the highest point; the trough, that’s the lowest. The amplitude is the distance from the resting position to the crest or trough, and it tells you how “strong” or “loud” the wave is, sort of. The period is how long it takes one complete wave—crest to crest or trough to trough—to pass by a point.

Ethan Miller

And there’s this classic formula teachers always bring up—the wave equation: v equals f times lambda, or v = fλ. So, “v” is the wave speed, “f” is frequency—how many waves per second—and “lambda” is just the wavelength, which is the distance between two consecutive crests, or troughs. You use this thing for calculating, like, how fast sound moves through air, or the speed of a ripple across a pond. It’s honestly not as scary as it looks.

Samantha Davis

Yeah! At my school’s science fair, we did this rope experiment. We’d shake one end and count how many peaks passed by in a second—that gave us the frequency. Then, we measured how far apart those peaks were—that was the wavelength. We could even figure out the speed of the wave using the equation. It was kinda wild, seeing the maths come to life in an experiment. Also my arms were sore for, like, a day—but science pain is temporary, right?

Emily Clarke

Absolutely. I mean, it’s easy to forget that everything on those graphs has a physical meaning. If you know what each bit is telling you, suddenly, the maths isn’t just numbers—it’s about the real energy moving through the world. And that’s what gets me excited about physics.

Oliver Bennett

Let’s see what happens when waves hit something—reflection. It’s probably the most familiar wave behaviour around. When a wave hits a boundary—like the edge of a pond, or a mirror for light—it bounces back. We call that the law of reflection: the angle that the wave hits the surface is the same as the angle it leaves. Simple as that.

Ethan Miller

Yeah, and you totally see this with echoes, right? You yell into a canyon and you hear your own voice bounce back. That’s sound waves reflecting off the wall. But it’s not just fun and games—this stuff shows up in tech too. Like, ultrasound imaging in hospitals uses wave reflection, and sonar on submarines bounces sound waves off objects underwater to figure out where things are.

Oliver Bennett

Oh, speaking of bouncing waves, I had this great demo in class once. We got a water tank, put a board down at an angle, and made small waves. You could see the waves hit the board and reflect right off—almost like a mirror, but with water. Everyone loved it, especially when they made a mess! But the big idea is, whether it’s water, sound, or light, the principle is the same—and it’s all about waves interacting with boundaries.

Emily Clarke

Yeah, that’s what makes waves so fascinating! They’re not just, like, a school topic—they actually explain so much in the real world. Once you see it, you can’t unsee it—waves really are everywhere.

Samantha Davis

And I guess that’s a wrap for today—waves are, uh, way cooler than I thought when I was a student, not gonna lie. Thanks for joining us, everyone! Keep those questions coming for our next episode!

Oliver Bennett

Yeah, absolutely. Hope this made waves, no pun intended, a bit easier. Thanks to all of you for listening!

Ethan Miller

Catch you all next time—don’t forget to review if you found it helpful. Bye guys!

Emily Clarke

Bye everyone! Can’t wait to dive deeper next episode. Take care!