The American holiday of Thanksgiving comes with one nationwide tradition -- turkey! Millions of people throughout the United States sit down to a big meal that has turkey as its main course. Turkey is a tradition because this is what people believe the pilgrims ate when they celebrated the first Thanksgiving in 1621.

For many people, the turkey cooking in the oven comes with another tradition -- the pop-up timer! This simple piece of technology lets everyone know when the turkey is done -- when the red indicator stick pops up, it is time to eat!

Did you ever wonder how that red stick knows that the entire turkey is finished?Now, we will focus on how the pop-up timer determines the cooked state of the turkey that will soon be your meal!

A Funky Thermometer!
Turkey is done when it reaches 185 degrees Fahrenheit (85 degrees Celsius). If you didn't have a pop-up timer, you could use a meat thermometer to figure out the temperature of the meat. But the pop-up timer, which often comes with a turkey that you buy at the grocery store, can be more fun because it is binary -- there's no trouble reading a pop-up timer because the answer is either "Yes" or "No"!

A pop-up timer found in a turkey or chicken normally has four parts:

On the left is a pop-up timer before cooking, and on the right is the same timer after it has popped up.

The soft metal (shown in gray in the diagram) is solid at room temperature and turns to a liquid (melts) at about 185 degrees Fahrenheit (85 degrees Celsius). When the metal turns to a liquid, it frees the end of the red stick that had been trapped in the metal. The spring pops the red stick up and you know the turkey is done!

One little-known fact is that these timers are reusable. If you dip the tip in hot water it will re-melt the metal and you can push the pop-up piece back into the metal. Then let it cool, and the pop-up piece will be back in its original position -- ready to use again!

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