The bluffer's guide to physics in everyday life

February 18, 2014
Article Promo Image

Life is full of strange things, with inner workings hidden to all but the most studious engineering folk. Save yourself a physics degree, and allow me to enlighten you on how lasers, yo-yos, trumpets, mood rings, microwaves and popping candy work.

Popping candy

“Pop Rocks” is not just a name: the candy literally explodes in your mouth. This is because within each delicious ‘rock’ are little pressurised bubbles of carbon dioxide.

Pop Rocks start their life as thick sugary syrup. In order to create the explosive popping effect, the syrup is mixed with pressurised carbon dioxide as it’s cooling, causing little pockets of high pressure gas to appear.

After being broken up and packaged, the rocks wind up in your mouth, where your saliva begins to dissolve the candy around the pressurised cavities. When your saliva breaks through, it creates a gap for the 600 psi carbon dioxide to leak out, and the sudden release of pressure explodes the entire rock apart.

“Wait a minute,” I hear you stutter. “600 psi? Surely there’s some sort of mistake!”

No mistake: 600 goddam psi.

Let’s put this into perspective:

Car tyres: 30 psi

Aerosol can: 100 psi

Steam train boiler: 200 psi

Pop rocks: 600 psi

That’s a lot of pressure. In fact, I’ve done the calculations, and if you were to get one single Pop Rock the height of the Sydney Harbour Bridge, it would contain the same amount of energy as the atomic bomb which flattened Hiroshima. So here’s hoping no-one actually builds that.

Pop Rocks


First, a primer on light and atoms. Light is created by electric or magnetic things moving, which causes waves in the electromagnetic field like a rock creates ripples in a pond. We see these waves as light, with a colour which depends on how close together the ripples are (how fast the wiggling was).

Because of this, when electrons move, they make their own light: it’s possible to ‘excite’ electrons around an atom, making them snap back and forth, causing a ripple. The size and frequency of this ripple depends only upon how many protons and neutrons each atom has, which means the colour of light emitted is different for each and every atom. (It’s because of this that we can work out what the atmospheres of distant planets are made out of).

So, a laser is basically a device which stimulates atoms that all have the same electrical properties. It consists of a cylindrical core of ruby, with a mirror at one end, and a partially reflective mirror at the other end which lets some light pass. A high-energy lamp coils around the ruby cylinder, and releases a flash causing electrons around ruby atoms to get excited and start emitting light. These wiggles in the electromagnetic field bounce off the mirrors and bump into other ruby atoms, exciting them, which creates more light, and so on. We now have a whole lot of light bouncing around, some of which escapes through the partially silvered mirror, causing a laser beam.

Now go blind your friends!


Microwave Ovens

The ‘microwave’ spectrum is a range of light frequencies, below the visible spectrum. Like laser light, microwaves are made up of ripples in electric and magnetic fields. Because of this property, microwaves will jiggle around any charged particles they come into contact with. This is the same basic principle which causes a magnet to jiggle around metal filings, or a charged balloon to move human hair.

A microwave oven emits microwaves from a generator in its side. When the microwaves hit the water molecules, they wiggle and rotate. Given heat is really just the movement of particles, this movement comes across as heat, and begins to cook your food.



When it comes to yo-yos, the way down is fairly simple. As you release the yo-yo, gravity pulls the main part of it downwards to the ground. At the same time, the string coiled around the yo-yo’s core forces it to spin as it unravels. Easy peasy.

The magic happens when the yo-yo has reached the end of the string. Let’s start with the old-school design. In an old-fashioned yo-yo, the string is tied tight around the core, preventing it from spinning on the spot. Upon hitting the bottom, the yo-yo will still want to keep on rotating because of the rotational momentum it’s built up while unravelling – spinning things generally don’t want to just stop spinning. So, it keeps rotating around, and starts to coil the string up the other way. Given the other end of the string is attached to your finger, this coiling movement leads to the yo-yo climbing its way back up to the top, ready to start all over again.

In a modern yo-yo, however, the string is tied only loosely around the spindle, allowing it to freely rotate on the spot. This is how you’re able to do cool tricks like walking the dog: the yo-yo just keeps on spinning without climbing. So, how do you get it to come up again? Well, when pulled up sharply the string is forced against the spindle which causes friction. The friction causes the string to ‘grab’ the spindle, and as long as there is enough rotational momentum, the yo-yo will start climbing again.



First the basics: sound waves are just periodic compressions in the air. You can see this when you look at a speaker: its back-and-forth movement pushes air forward, then pulls it back, creating a “compression wave”. The frequency of this compression determines the pitch of the note played.

A trumpet generates compression waves too. But instead of a speaker creating the compression, we have the trumpeter’s lips (or to get technical, the trumpeter’s ‘embouchure’). As the player’s lips flap up and down against a trumpet’s mouthpiece, like they’re blowing a raspberry, air is forced through their mouth and then blocked off periodically, causing a wave of pressure in the air travelling through the trumpet’s tube.

Now here’s the weird part: when this wave hits open part of the trumpet (the bell) at the other end, a wave is reflected back towards the lips. Why? Well, think of it like when a big truck passes by, and a breeze is sucked in behind it. The sucking after the pressure has passed causes another pressure wave, this time travelling the opposite direction.

Trumpeters are trained to puff air at a speed causing a “standing wave” to occur (read here for a bit more detail – they’re pretty fascinating). The frequency of a standing wave depends on the length of the tube it’s occurring in, so a longer tube gives you a lower sound, and a higher tube gives you a higher sound. This is where a trumpet’s keys come in: the keys block off and open up different lengths of tube, causing the tube to become longer or shorter, and thereby changing the pitch of the notes.


Mood Rings

Let’s just get this over with: mood rings don’t actually track your mood. In fact, the gems inside the rings aren’t gems either, they’re a liquid. What looks like the ‘stone’ in a mood ring is a hollow, glass shell filled with liquid crystals. The liquid crystals are arranged naturally in layers with regular spacing between them. When light hits these layers, it is reflected back with a wavelength which depends on how big the spacing is, meaning that the colour of light depends only on how far between these layers are. When the liquid crystals are heated, the spaces between them shrinks, meaning the light will change based on temperature.


Rupert Parry

Rupert Parry is currently studying a Bachelor of Arts and a Bachelor of Science at The University of Sydney. Rupert is editor and co-founder of the Larrkin Post and works part-time as a videographer and designer. He plays guitar in his band, The Tropics, and has the ability to eat large spoonfuls of wasabi without so much as a flinch.

Photo: Beyond Neon