In theory, waves can go on forever and ever! What that means is that if you, or I, could travel faster that the microwaves that we use for our cell phones, we could get to a point in outer space before our conversations got there and know what was going to be said!

But we can’t do that! Realistically, they are limited by the size of the system. –This is why waves don’t keep going on and on, but why don’t radio waves do this? They do! –It’s the curvature of the Earth that limits the range of radio waves. Where do radio transmission emanate from? –Towers, Really tall towers. Why? So they can reach out beyond your line of sight. –You can only see just so far because of the curvature of the earth. The farther away you get the lower you appear on the horizon. »With a tall tower the transmission of the radio waves can reach out to the point where the tower too drops out of sight below the horizon.

The taller the tower the farther the transmission, “+ or –” obstacles.

The size of the parameters is really what allows these waves to be as big as they are or as small as they are. The boundaries and properties of the system are what make certain waves more powerful than others. The concepts of Resonance and Natural Frequency apply to a huge range of natural and man-made systems. These two powerful ideas are the key to understanding the tides of the ocean and the way our ears separate the sounds that we hear, even how a microwave oven works!

Natural Frequency What is natural frequency? This is the frequency at which a system oscillates when it is disturbed. If you pluck a guitar string at a certain point it vibrates back and forth with a certain frequency. Pluck it in the same point as many times as you what and it will always vibrate with the same frequency. This is known as the Natural Frequency. –It is a controlled oscillation!

Why do you want a material to have a Natural Frequency? Everything in the Universe has a natural frequency, and many have more than one! If you know an object’s natural frequency, you’ll know how it will vibrate. –Structural engineers, the people who design and build office buildings, skyscrapers, etc. want to know this. Especially in an earthquake prone area. If you how an object vibrates, you’ll know what kind of waves it will create. –Ship builders take note of this characteristic. If you want to make specific kinds of waves you need to create objects with natural frequencies that match the waves you want. –The music industry is interested in this aspect.

Here are just a few of the things that you and I rely upon that have natural frequencies that we’ve put to good use. Microwave Ovens –The waves are used to heat the moisture trapped within the food that you are warming up. Musical Instruments –The different tones, pitches, etc. are well know to all of us. Cell Phones –Your phone number is the natural frequency that has been assigned to you and only you! That’s how you keep you calls private. But that wasn’t always the case. –When phones were first invented and put to public use they used a system called the “Party Line.” »When your phone rang, so did several others at the same time in different locations. »Everyone picked up and they then trusted those not involved to hang up.

Sometimes we want to change the natural frequency of an object. In order to do this we have to change some of the external forces that are acting on the system. We can change the natural frequency of a system by changing the size, inertia, or other forces on the system. For example you can tune a guitar or a piano by tightening or loosening the wires that are used to make the frequency.

There are times when you want to keep a system vibrating, or oscillating. For example, when you are on a swing. How do you get it going? All at once, or does it take a little time? And once you find the perfect speed, do you have to do anything to keep that going? The time period, when the oscillation is just right and everything is going as planned is called Resonance.

Resonance Resonance is an interaction between a wave, a driving force, and the boundaries of the system. The force is synchronized with the frequency (Period) of the wave allowing it the most efficient way to work. The boundaries of the system keep the force from becoming too great, or not allowing to work with too little effort. What this means is that once the natural frequency is reached, minimal effort is required in order to keep the natural frequency occurring. –The initial expenditure is large, but then it tails off as the natural frequency is maintained.

Where do we see resonance?