The Main Idea: Water is exceptional.
Materials:
water baking sheet
plastic wrap aluminum foil
pin salt
rubber band rice
liquid dishwashing detergent thermometer
oven and cooktop/stove 2 mugs
Will the Raindrops Fall?
Water is a sticky substance, which explains why moisture in the air condenses into tiny droplets, as seen within a cloud or fog. These tiny droplets, in turn, coalesce into larger drops that fall, as seen with rain. So what happens when a glass of water covered with plastic wrap punctured with many tiny holes is turned upside down?
Procedure:
- Fill a tall glass with water and cover it with plastic wrap held taut with a rubber band around the rim.
- Use a pin to poke many tiny holes into the plastic wrap directly over the mouth of the glass.
- Predict what will happen when you turn the glass upside down over a sink. Will there be many tiny streams of water? Will a shower of raindrops form and fall? Will the water mostly not pass through the holes? What do you predict?
Analyze and Conclude:
Explain your observation in terms of the stickiness of water molecules.
- Is there any difference when you hold the glass still and level versus when you shake the glass or hold it at an angle?
- Swirl some liquid dishwashing detergent into the water in the glass. Do you get the same results?
- Assume you did the same activity using a wide-mouth plastic bottle with a hole drilled into the bottom. (You’d still have plastic wrap with tiny holes over the top, but now you have a hole in the bottom too.) What results would you expect then when you turn the bottle upside down? Why?
Think and Do
27a. Place a cup of salt and a cup of rice side by side on some aluminum foil laid out on a baking sheet. Heat the salt and rice for 10 minutes in an oven preheated to 250ºC. Which has a higher temperature when you first take it out of the oven?
27b. Pour the salt and the rice into two separate mugs. Which cools down faster? If you don’t have a thermometer, judge their cooling rates by cautious touch.
27c. Which has the lower specific heat? (review from ch. 3)
27d. Why does the heated rice adhere to the side of the mug?
99a. Use a thermometer to measure the temperature of boiling water. Record the temperature below:
Sample Solution
