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• One of the most striking properties about life is that it has color.

• To understand the phenomenon of color, it helps to think about light as a wave.

• But, before we get to that, let's talk a little bit about waves in general.

• Imagine you're sitting on a boat on the ocean, watching a cork bob up and down in the water.

• The first thing you notice about the motion is that it repeats itself.

• The cork traces the same path over and over again... up and down, up and down.

• This repetitive or periodic motion is characteristic of waves.

• Then you notice something else...

• using a stopwatch, you measure the time it takes for the piece of cork to go over its highest position down to its lowest and then back up again.

• Suppose this takes two seconds.

• To use the physics jargon, you've measured the period of the waves that cork is bobbing on.

• That is, how long it takes a wave to go through its full range of motion once.

• The same information can be expressed in a different way by calculating the wave's frequency.

• Frequency, as the name suggest, tells you how frequent the waves are.

• That is, how many of them go by in one second.

• If you know how many seconds one full wave takes, then it's easy to work out how many waves go by in one second.

• In this case, since each wave takes 2 seconds, the frequency is 0.5 waves per second.

• So enough about bobbing corks... what about light and color?

• If light is a wave, then it must have a frequency, right?

• Well... yes, it does.

• And it turns out that we already have a name for the frequency of the light that our eyes detect.

• It's called color.

• That's right. Color is nothing more than a measure of how quickly the light waves are waving.

• If our eyes were quick enough, we might be able to observe this periodic motion directly, like we can with the cork and the ocean.

• But the frequency of the light we see is so high, it waves up and down over 400 million million times a second that we can't possibly see it as a wave.

• But we can tell, by looking at its color, what its frequency is.

• The lowest frequency light that we can see is red and the highest frequency is purple.

• In between all the other frequencies form a continous band of color, called the visible spectrum.

• So, what if you had a yellow pencil sitting on your desk?

• Well, the sun emits all colors of light, so light of all colors is hitting your pencil.

• The pencil looks yellow because it reflects yellow light more than it reflects the other colors.

• What happens to the blue, purple and red light?

• They get absorbed and the energy they are carrying is turned into heat.

• It's similar with objects of other colors.

• Blue things reflect blue light, red things reflect red light and so on.

• White objects reflect all colors of light, while black things do exactly the opposite and absorb at all frequencies.

• Thisby the wayis why it's uncomfortable to wear your favorite Metallica t-shirt on a sunny day.

One of the most striking properties about life is that it has color.

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# 【TED-Ed】What is color? - Colm Kelleher

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VoiceTube posted on 2022/02/18
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