How do science concepts apply to your world? Here are some questions you'll be able to answer after you read this chapter.

• When a car has been warmed by the sun, why is the metal door hotter than the plastic bumper?
• Why doesn't hot air burn your unprotected arm when you reach into an oven?
• Why does a bicycle pump heat up when you pump up a tire?
• Why must a car engine have a cooling system?
• Can you cool a kitchen by leaving the refrigerator door open?
• What energy-saving strategies are used in a solar-heated home?

What Happens When Hot and Cold Liquids Mix?

Procedure

1. Fill one graduated cylinder with hot water and another with cold water. CAUTION: Be careful when handling hot liquids. Use a thermometer to measure the temperature of the water in each graduated cylinder. Record the temperatures.
2. Pour 100 mL of hot water into a plastic foam cup. Add 100 mL of cold water to the cup. Stir the water with a glass rod, and measure and record its temperature.
3. Repeat Step 2, this time adding 50 mL of cold water to 100 mL of hot water.

Think About It

1. Comparing and Contrasting   How did the final temperatures in Steps 2 and 3 compare?
2. Relating Cause and Effect   What factors can you identify that determine the final temperature when you mix hot water with cold water?
3. Controlling Variables   Why do you think it was important to use the same graduated cylinders in Step 3 that you used in Step 2?