Activity 1: How Do We Solve a Mystery?
Scientists use the same techniques as detectives to solve mysteries: They gather evidence, from which they create one or more working ideas or explanations as a basis to test their ideas.

Mystery: Why a CD player doesn't work.

What if you put a CD in your CD player, turned it on, and nothing happened? Let's apply these mystery-solving techniques to the question to see if they can help us figure it out. And keep in mind that one of the most important elements in scientific investigation is to first look for the simplest explanation.

So let's start with the simplest questions:

Gather Evidence:
If you use an electrical outlet to play your CDs, is the CD player plugged in?

Working Explanations:
If NO, this is probably the answer. That was easy, wasn't it?
If YES, the player is plugged in, try this:

Testing Ideas:
Try the plug in another socket. Or test the socket by plugging something else into it, a small lamp or appliance that you're sure works.

Gather Evidence:
If you use batteries to play it, are they inside and intact?

Working Explanations:
If NO, this is probably your answer.
If YES, maybe the batteries are dead.

Testing Ideas:
Is there some other appliance/machine that you can test them on? Or maybe you're one of the lucky people who have their own battery-tester.

Gather Evidence:
Does the CD player look damaged in any way?

Working Explanations:
If YES, this could be your answer.
If NO, move on.

Gather Evidence:
Have you tried to play this particular CD before?

Working Explanations:
If YES, and it worked before, it's probably the player.
If NO, there might be something wrong with the CD.

Testing Ideas:
Try another CD. Does that work?
Working Explanations:
If YES, it's probably the CD, not the CD player. And there's your answer.
If NO, it's probably the player.

You've looked for and eliminated the simplest answers. Now the questions get a little more complicated. Let's try one.

Gather Evidence:
Assuming the player worked the last time you used it, did someone else use the player since then? (Here you have to go beyond your own observations and ask the people who had access to it—your family, possibly your friends—if they used it.

Working Explanations:
If NO, ask someone else (until you've asked everyone you can think of).
If YES, ask them if the player worked when they used it.

Working Explanations:
If YES, that is, they say the player worked when they used it, something must have gone wrong between the time they used it and now. But what?
If NO, you've at least established that someone tried to use it and it didn't work.

To take your investigation further, you'd probably have to do some research, which is what many scientists do when their investigations take them into unfamiliar territory. In this case, CD players contain extremely complex components—the problem could be with the motor or the laser or some tiny little switch. If you were determined to find out why your CD player wasn't working, you'd have to learn more about what makes a CD player work in the first place.