} CAS: Teachers - Dry My Laundry!

Teachers > Lessons & Kits > Lesson Plans > Pre-Visit Activity: Dry My Laundry!

# Pre-Visit Activity: Dry My Laundry!

### Abstract

In this activity, students will practice designing a basic controlled experiment and discuss how surface area affects evaporation in preparation for their Troubled Tree Frogs Student Lab Program.

We recommend using the Troubled Tree Frogs Scavenger Hunt during your visit to the California Academy of Sciences.

### Objectives

In this activity, students will:

1. practice designing a basic controlled experiment involving evaporation
2. compare the results of their experiment
3. discuss how surface area affects evaporation
4. prepare for their Troubled Tree Frogs Student Lab Program

### Materials

• paper towels
• scissors
• water
• string
• clothespin, or other clip that can be used to suspend the paper towel t-shirts
• plastic plates or other surface for drying

### Vocabulary

• surface area: the area of an object exposed to the air
• evaporate: to change from liquid water to water vapor

## Preparation

1. Cut identical t-shirt shapes out of paper towels.  You may choose to do this activity as a demonstration, or with students in groups.  This will determine how many paper towel t-shirts you will need.  At minimum, you will need one paper towel t-shirt for each experimental design the students come up with.

## Introduction

• Go over the term evaporation with your students, eliciting examples of evaporation in their daily lives.  Tell the students that when they visit the California Academy of Sciences, they will be looking at how evaporation affects frogs.
• Tell them that before their trip, they are going to experiment with evaporation and figure out the conditions under which evaporation happens fastest.

## Procedure

1. Have students imagine that they are walking home from school and it starts to rain unexpectedly.  Your clothes get soaked!  You are wearing your favorite t-shirt and you really want to wear it later that day.  You want to conserve energy, so you don’t want to run the dryer for just your t-shirt, and laundry day was yesterday! What’s a kid to do?
2. Ask students to brainstorm the best way to get the t-shirt dry.  Would you want to ball it up and throw it under the bed?  Why not?  Write up responses on the board/overhead.  Potential responses could be to wring it out, hang it up, lay it on a table, hang by a window, etc.
3. Wet towels under the faucet and squeeze out excess water. **This activity works well if the paper towel t-shirts are damp, not soaking.  (If you have chosen to do this as a demonstration, with your paper towel t-shirts, model each reasonable response.  Include a t-shirt that is wet and remains balled up.  If this will be a group activity, each group can set out their own paper towel t-shirts based on their own ideas.)
4. Have the class make a prediction as to which paper towel t-shirt will dry up the most.  Make sure they explain the reasons for their top choice.
5. Allow time for the paper towels to dry somewhat, around 30 – 45 minutes.  Time will vary depending on the conditions in the room (temperature, air flow, etc.).  This time should give hanging t-shirts time to almost dry, while balled up t-shirts clearly remain wet.
6. Come back to the experiment and compare the results.  Compare the relative dampness of each t-shirt.

## Wrap-Up

Keeping answers open-ended, discuss with the students:

• What do you notice about which method dried the t-shirt the most?
• What conditions (variables) were different for each t-shirt?
• Which method had the greatest surface area (the most material exposed to the air)?
• What can you conclude about evaporation and surface area?

### Investigation and Experimentation

• 6c. Formulate and justify predictions based on cause-and-effect relationships.

### Earth Sciences

• 3b. Students know when liquid water evaporates, it turns into water vapor in the air and can reappear as a liquid when cooled or as a solid if cooled below the freezing point of water.

### Investigation and Experimentation

• 6e. Identify a single independent variable in a scientific investigation and explain how this variable can be used to collect information to answer a question about the results of the experiment.
• 6h. Draw conclusions from scientific evidence and indicate whether further information is needed to support a specific conclusion.

### Investigation and Experimentation

• 7a. Develop a hypothesis.
• 7e. Recognize whether evidence is consistent with a proposed explanation.

### Investigation and Experimentation

• 7c. Communicate the logical connection among hypotheses, science concepts, tests conducted, data collected, and conclusions drawn from the scientific evidence.

### Investigation and Experimentation

• 9c. Distinguish between variable and controlled parameters in a test.

### Background

While the following information is not necessary for this pre-visit activity, some of the key concepts will be introduced in an age-appropriate manner during the Student Lab Program.

Many of the potential threats faced by tree frogs arise from their characteristic skin: a thin, scale-less, moist layer that easily exchanges water and gases with the environment.  Sometimes this permeable skin is an advantage.  For example, many frogs have a ‘seat patch’ on their rear end, a special section of tissue that absorbs water particularly well.  So instead of drinking through its mouth, a frog can stick its bum in a pool of water to quench its thirst!

Frog skin also performs an important role in frog respiration.  Because the lungs of an adult frog are hollow sacs, surface area is minimal and the exchange of gases is less efficient than in mammals.  Frogs don’t inhale and exhale regularly like humans, dogs, and cats, but rather take in large gulps on occasion.  The majority of a frog’s gas exchange is instead performed through its moist skin.  Oxygen from the air dissolves in a layer of mucus covering the body, diffuses through the skin into the bloodstream, and travels to the frog’s cells.  In summary, a frog both drinks and breathes through its skin!

The large surface area of the skin relative to a tree frog’s volume is thus helpful for providing the body with plenty of water and oxygen.  However, this skin can become a handicap when the environment is not ideal.  For example, acid rain, water pollution, natural toxins, and fungus, can injure a frog’s sensitive skin, or easily pass into the body.  Water loss due to evaporation from the skin is also a great physiological danger.  Variables such as low humidity, heat, and high wind increase the rate of water evaporation, leaving a frog vulnerable to dehydration.  Without water covering its body, the frog will have a tough time capturing enough oxygen for its cells!