Turn on the Radio!

A photo of my radio tuned to Power 104,300,000 Hz.

As soon as I sat down in my car today to go for a drive, I tuned my radio to Power 104.3 and heard the sweet sound of Taylor Swift’s “I Knew You Were Trouble” blasting through the speakers. Throughout all of the year’s that I’ve listened to the radio, I’ve always asked myself, “Why am I hearing this broadcast and why do I hear different broadcasts when I change the number on my radio’s tuner?” I always knew that radios worked because of transmission and reception of sound waves in the air, but, to be honest, I barely knew what a sound wave even was. Now, with sufficient knowledge of the physics of sound, I can easily explain to myself (and to all of you readers if you’d like) how you too can hear Taylor Swift blasting through your radio’s speakers.

A photo of me and a Taylor Swift life-size cut out.

When you tune your car’s radio to a radio station, for example, Power 104.3, have you ever asked yourself what those numbers actually mean? I didn’t think so. 104.3 is short for 104.3 MHz (megahertz.) That is, 104,300,000 Hz. Hertz, as we all know, is a frequency, represented by the equation f=1/T, where T is the period, the amount of time a sound wave takes to make a complete oscillation. We don’t necessarily need to know this, but the period of Power 104.3’s sound wave is T=1/104,300,000Hz=9.58×10^-9s, now that is one fast period! It makes sense that an FM radio station’s period would be so fast, it needs to transmit a lot of information really quickly in order to make a high quality broadcast. This explains why AM stations are not as high quality as FM stations, AM frequencies are only in kHZ as opposed to MHz.

Now that we’ve explained the basics of frequencies and periods of sound waves, how does your radio pick up these waves and relay their broadcast to your speakers? This is simple. Let’s use Power 104.3 as our example. Power 104.3’s transmitter’s sine wave has a frequency of 104.3MHz as previously stated. That’s great. We have a really fast sine wave moving through the air. Now what? Your car’s radio has a receiver complete with an antenna, tuner, and an amplifier. The radio receiver’s antenna picks up all of the radio sine waves traveling through the air. The tuner’s job is to then separate the one sine wave you want from all of the other sine waves. In our case, the tuner separated the 104.3MHz sound wave from all of the others. You may be asking, how does the tuner do this? That’s simple too. Tuners work using a principle called resonance. That is, the tuner resonates at one particular frequency and ignores all other frequencies in the air. Finally, the tuner sends the signal that it receives from a particular frequency to the radio’s amplifier, which ultimately amplifies the sine waves to your car’s speakers. Viola!

There you have it everyone, the physics of radios. Look above you! You see those? Those are radio waves. Thousands of them. Care to listen? Tell your tuner to resonate where you want it to!

A HOT Marathon!

Today I ran the 26.2-mile Honolulu Marathon and realized what pain is for the first time. Never before had I felt so tired, beat-down, and helpless. To my delight, everything was going just fine for the first half of the race. Then to my dismay, a couple things changed: the sun came up and I felt as if I could barely walk on my knee. What was I going to do? I really wanted to finish the marathon and wear my finisher shirt with pride, so I forced myself to keep pushing. Although it was extremely hot, there were water and ice stations throughout the race which cooled me down (stole some of my body’s heat). Having just taken my AP Physics B Thermodynamics test on Friday, I started to mentally explain to myself why I was hot and why the ice cooled me and my injured knee down. Heat is transferred by three main mechanisms: radiation, convection and conduction, all of which I experienced today. It really is just simple Thermodynamics.

A photo of me rounding a corner in Hawaii Kai.

The reason why I became hot when the sun came up is because of radiation, the movement of energetic waves or particles. The sun’s rays, forcefully beating down on me as I ran, undoubtedly heated me up a bit. The sun did not just heat me up, however, it heated up the black asphalt, which then heated me up even more.

The reason why the black asphalt heated me up is because of convection, the movement of molecules in fluids. The black asphalt absorbed a large amount of heat from the sun’s radiation and then transferred that heat in the air through convection. No wonder why it was so hot running on asphalt as opposed to when I was running on grass; grass does not absorb heat as well as asphalt!

Although radiation and convection were heating me up like crazy, I was able to cool myself down with some ice that I found at water and ice stations throughout the race. Hot, tired, and feeling dead, I grabbed a handful of ice from the aid station and rubbed it on my knee and neck. Why did I feel as if the temperature of my leg and kneck were getting lower? Obviously there was some conduction (the transfer of heat through matter) going on here. When I put the ice on me, heat immediately started to transfer from my body to the ice cube, ultimately melting the ice cube. The poor ice cube was not receiving heat just from my body, it was receiving heat from the same radiation and convection that I was experiencing too! Poor ice cube 😦

My ice cubes weren’t the only things that melted today. My heart melted when, to my surprise, Jordan was waiting for me at the finish line 🙂 Would that be radiation, convection, or conduction? I don’t know.

During the race, I wished that the laws of thermodynamics did not apply to ice cubes. If the ice never melted, I would’ve been a lot more comfortable when I was running. Oh well. Although the marathon was probably the hardest thing I’ve done in my whole life, I’m glad that I did it and I’m thankful to be sitting in my air-conditioned room as I write this week’s physics blog. Tired and worn-out, I’m having trouble thinking right now, so let’s save the discussion on air conditioning for another time.