[DOOR CLICKING SHUT]

Don: Oh no!

Yael: What's wrong?

D: I locked myself out of the office.

Y: OK, all I need is a paper clip and I'll open the door.

D: You mean you'll pick the lock?

Y: Yep.

D: Cool. How does it work?

Y: When you put a key in a lock and twist, you turn a part called the cylinder. The      cylinder then turns a part called the cam, which makes the bolt slide in or out,      depending on which way you turn.

D: But how does a key make the cylinder turn?

Y: I'm getting to that. Inside a lock are several shafts running through the cylinder and      into the casing around the cylinder. Inside these shafts are pins of various lengths.      Without a key inside, the bottom half of each pin rests inside the cylinder, while the      top of the pin extends beyond the cylinder to the surrounding casing. This is what      holds the cylinder in place: if you try to twist the cylinder without correctly moving the      pins, the top pins will catch on the casing.

D: That's where the correct key comes in.

Y: Yep. When you insert the right key, its notches raise the pins just enough so that the      bottoms of the pins are aligned with the space between cylinder and casing. Since      none of the pins is in both the cylinder and the casing at the same time, the cylinder      turns freely.

D: So when you pick a lock, you're using a paper clip or whatever to push the pins up      like the correct key would.

Y: Exactly. Wait a second . . . There you go. Your lock has been picked.  

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A Moment of Science®