## Chapter 18

### Part 1: Home and School Investigation

Send the Letter to Family (PDF file) home with each child. Once all the children have done the comparisons at home, ask them to share, one at a time, with their classmates how they went about finding out which container held the most water. You might want to have two containers of different sizes and some water that they can use for demonstrating.

### Part 2: Be an Investigator

A good time to do this investigation is after Lesson 1 on cups, pints, quarts, and gallons.

#### Materials

- 3 clear cylindrical glasses of different diameters, labeled A, B, and C
- one-cup liquid measure
- water
- strip of cardboards, labeled A, B, and C

#### Introducing the Investigation

Ask children what happens to puddles of water on the ground. Why don't they just stay there? Get children talking about how the hot sun dries them up. Introduce the term **evaporation** and talk about how water becomes part of the air.

Show children the glasses. Tell them you are going to fill each glass with the same amount of water. Each day you will measure how much water is left in the glasses by making a mark on the strip of cardboard with the same label as the glass. You will hold up that strip of cardboard to the glass at the base of the glass and mark the water level on the strip of cardboard. Each day you will ask the children to predict which glass of water will totally evaporate first, allowing them to change their prediction from the previous day if they want to.

#### Doing the Investigation

Rates of evaporation vary from place to place. Decide on the right amount of water to start with in each glass so that the water will evaporate within a few weeks. You may want to do the measuring every few days or once a week to get a noticeable difference in the water level.

Continue this investigation until the water in one of the glasses is gone. Ask the children why they think the water in that glass evaporated first. If the children don't mention diameter, point out that the glasses had different diameters (different sized circles). Some children may be able to understand that the glass with the most water exposed to the air had the highest rate of evaporation. Since this is a very sophisticated concept, don't be concerned if children don't fully understand it. It is through many experiences such as this that they learn how the world works.