A Pulling Force

Thursday I had the pleasure of teaching the students about surface tension through a lesson called, “The Pulling Force.” I had everyone sit on the edge of the carpet to form a circle while I demonstrated how to place drops of water from an eyedropper onto a penny. The children watched and helped me by remembering how we are very careful and slow with the eyedropper because we do not want it to become a squirt gun. Earlier in the day the children learned how to make tally marks when counting and they used this new skill to keep track of the amount of drops that would stay on the penny. We made some predictions as a class and they made individual predictions before partnering up and conducting their investigation. The children had a great time in their discovery and learning how to use scientific tools. To close the lesson, we talked about how many drops fit on our penny, what the penny looked like, and how the drops of water stuck together. We talked about how surface tension is like the skin of water. Our own skin stretches and moves so that all of our water, blood, muscles, and bones can stay inside of our body. The students also used their tally marks so well and I was impressed by their involvement and desire to learn.

Learning Cycle (Guided Discovery) Lesson Plan Format

Name Joanna Lende Date Grade/Subject K1 Math Time Allotment 30-45 min

Classroom Structure: (e.g. cooperative grouping arrangements, large group/small group)

Context: (identify which lesson within a unit.. e.g. new concept, review of concept) This is a math lesson for the Power of Water unit.

Materials and Preparation:

For each pair of students

• 1 penny with well defined edges
• 1 eye dropper
• a small cup of cool water
• a student page entitled “A Pulling Force”

Objective: Teach students about surface tension of water through their own explorative discovery. Students will become familiar with scientific study and know how many water drops can fit on a penny.

Assessment: Make sure one partner does not control the investigation. Observe and record participation by students.

Lesson

Introduction:

• Anticipatory Set: Water has high surface tension. Surface tension is a force that exists on the surface of liquids where the molecules pull at each other very strongly, forming a kind of “skin,” This property of water is what makes it form drops instead of spreading out into other shapes. How many drops of water do you think could sit on a penny?

Procedure:

1. Ask the class to bend their fingers so that their hand is opening and closing. Ask, “What happens to your skin when you bend your fingers?” “Does your skin break?” They should not that the skin stretched, but does not break.
2. Ask the students to think back to their experience with the water drop on waxed paper. Ask, “Why were you able to pull the water around on the paper?” “How is that like your skin?”
3. Explain that they are going to take a closer look at a collection of water drops. Hold up a penny and ask them how many drops of water do they think will fit on the penny. Have them predict and record their answers in their science notebook or their student page.

Concept Exploration: (students collect and record data, include open-ended questions)

• Have the one person from each pair of students collect a penny, eyedropper, and medicine cup with cold water.

• Place the penny on a level surface with the “heads” facing up.

• Have both partners practice counting water drops back into their cups before trying it with the stem of the eyedropper. Hold the eyedropper in a vertical position about ½ inch above the penny. Squeeze the bulb so that one-drop of water at a time falls onto the coin.

• Tally each drop of water that is dropped on the coin. Continue counting until the water begins to flow off the penny. Students record the number of last drop before the water flowed off the penny.

Concept Explanation: (whole group processes data, summarize results, provide vocabulary)

• Discuss what they observed.
• What happened to the water as you dropped it on the penny? (The water begins to forma bubble on the penny).
• What did you observe happening above the surface of the coin (The property of cohesion help the water molecule together and the property of adhesion help the water to the surface of the coin).
• Did you look at your water-covered penny from the side to make you drawing?

Concept Expansion: (new problem to extend concept, application of concept)

• Could you get more drops of water to stay on the “tail” side of the penny?
• Would warm water make a difference on the number of water drops a penny would hold?
• Would an older, worn down penny hold less water?

Closing:

• Closure: (students review or summarize)

• Independent Practice: (assignment allows students to practice or apply new skill)

Extension: (activities planned for students who finish early or for the whole class if time allows)

Optional Surface tensional experiment: leak proof fabric. Surface tension stops water form pouring through the tiny holes between the threads in woven fabrics such as cotton or gauze. This is why tents will keep rain out as long as we do not tough fabric and break the surface tension. This experiment shows how well surface tension prevents water leaking.

Materials

1. Large bottle or jar
2. Piece of find gauze bandage
3. Rubber band
4. Water

Procedure: Fill the bottle with water. Fix the gauze over the end with a rubber band. Turn the bottle over. The water will not flow out because surface tension acts like a skin to stop the water escaping through the holes in the fabric. Remind students that water also has a “skin.”

Learning Experience Scientist’s Name: _________________________

Activity

Student Page Date: ___________________________________

A Pulling Force

How many drops of water can be put onto the penny before the water begins to flow off of it?

My prediction: ____________drops

Tally each drop of water that you place on your penny here:

Draw a side view of your penny just before the water starts to flow off of it here:

The actual number of

drops that fit on our

penny was:_____________

You can seethe properties of water in nature. A water beetle takes advantage of surface tension to skim quickly across the water. The beetle is light enough so that it does not break the surface “skin.”