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Cohesion and Adhesion

Grades: 5-8
Author: Eugenia Johnson-Whitt


Abstract

Module Description

This module explores the difference between cohesion and adhesion. Participants observe and make predictions so that they can direct their students to do the same. First, participants are given various liquids and asked to make observations. Then, participants report their findings and compare the liquids. Operational definitions are addressed and discussed. Participants investigate factors that may affect the cohesion and adhesion of a substance.


Objectives

  • Participants will investigate the concepts of cohesion and adhesion.
  • Participants will investigate factors that may affect the cohesion and adhesion of a substance.
  • Participants will prepare and implement a lesson that incorporates an extension, using the content of this lesson and processes of science, giving due regard to best science teaching practices.

Materials

Locally store purchased items:

  • Corn oil - $1.29 per bottle (approx.)
  • Tap water - dyed blue
  • Soapy water - dyed red
  • Rubbing Alcohol - dyed green – $1.50 per bottle (approx.)
  • Elmer's Glue - $1.00 – 3.00 per bottle (approx.)
  • Paper towels - $2.00 (approx)
  • Five clean pennies - $.05

Classroom lab materials:

  • Small graduated cylinder
  • 4 droppers or dropping bottles

Graph paper


Procedures

Engagement

Begin participants thinking about cohesion and adhesion by showing participants several pictures or diagrams (if pictures are unavailable, ask participants to visualize these scenarios) - a bubble, a piece of bubble gum stuck to the bottom of a shoe, a gecko sticking to a wall, a raindrop, a roll of Scotch tape, and a dripping faucet. Ask participants what they observe about these pictures. Bring the conversation around to "stickiness".

Tell participants that in this experiment they will be predicting and then determining how liquids stick together and to each other.

Assessment: Monitor the participants' answers to your questions in the discussion. Be sure that they have some background knowledge to be ready to experiment.

Exploration 1

Review safety procedures for this lab (see Safety). Put participants in groups of 3 - 4 and assign roles (materials manager, lab manager, recorder). Distribute the following directions to the groups:

  1. Place ONE drop of the following liquids on a piece of wax paper:
    • Corn Oil
    • Tap Water (dyed blue)
    • Soapy Water (dyed red)
    • Rubbing Alcohol (dyed green)
    • Elmer's glue — use the bottle of glue for drops
  2. Observe the drops from the side and draw a picture showing the relative height and shape of each drop. Be sure to label the name of each drop.
  3. Why do you think that we put the drops on wax paper and not normal paper?
  4. Based on your observations, in what ways are the drops alike? Based on your observations, in what ways are the drops different?
  5. Which of the liquids held together best? Justify your answer.
  6. Which of the liquids held together least? Justify your answer.
  7. List the liquids in order of the MOST "together" to the LEAST "together".

Assessment: Monitor participants' work. Be sure participants are proceeding safely and following procedures.

Explanation 1

Participants report their findings and compare their lists of liquids. The facilitator introduces the terms COHESION and ADHESION as forces of attraction. Ask participants to analyze the word ADHESION for a clue to its meaning. What definition can your team give for ADHESION? Ask participants to analyze the word COHESION for a clue to its meaning. What definition can your team give for COHESION? Do not elaborate on examples of these properties or reasons why they occur at this point.

Assessment: Be sure that participants have a beginning understanding of the terms cohesion and adhesion.

Exploration 2

Distribute the following directions to the groups:

Procedures:

  • Take a new piece of wax paper. Place a drop of water on the wax paper. Quickly turn the piece of wax paper over and hold upside down. Describe what happens to the drop of water.
  • Does this happen because of adhesion or cohesion? Be sure to explain your answer.
  • Place two or three drops of water next to the drop on the wax paper. Describe what happens? Is this cohesion or adhesion?
  • Based on the results of your experience with the liquids, which of the liquids would you be able to put the most of on a penny with a dropper before it would spill over? Make a prediction.
  • Measure out how many drops of the blue water are in 1 ml using the small graduated cylinder.
  • PREDICT: How many drops of the following liquids can fit on the surface of a penny without spilling over? Write you predictions.
    • Tap Water
    • Soapy Water
    • Corn Oil
    • Rubbing Alchohol
    • Elmer's Glue
  • TEST YOUR HYPOTHESIS: Now test how many drops of each liquid can fit on the surface of a penny without spilling over. Place your pennies on a paper towel. Use a clean penny for each liquid. It is important to SLOWLY place each drop on the penny. Record your results.
    • Tap Water
    • Soapy Water
    • Corn Oil
    • Rubbing Alchohol
    • Elmer's Glue
  • Explain where is COHESION taking place?
  • Explain where is ADHESION taking place?
  • In what ways was the glue different from the other substances?

Assessment: Monitor students' work. Be sure students are proceeding safely and following procedures.

Explanation 2

Participants report their findings and compare results.

Return to a discussion of cohesion and adhesion. Give examples of these attractions (see Content Knowledge). Explain to participants that the molecular structure of water contributes to its exhibition of cohesion. Have participants draw several water molecules showing the dipolar interactions of the molecules and the force of attraction between them.

Return to the pictures shown in the engagement. Discuss them now in relation to cohesion and adhesion.

Explain to participants that they have demonstrated one of Howard Gardner's theory of multiple intelligences, the VISUAL/SPATIAL INTELLIGENCE. A student's preference for a particular intelligence greatly influences how that student learns. Remind participants to recognize and take advantage of the natural learning styles of all students, while helping them to improve the skills that are weaker. Once they become skillful at working with multiple intelligences, the more students will learn and your classroom will be more engaging.

Assessment: Ask participants to summarize their findings in writings and what they have learned about cohesion and adhesion as a result of their work. Check their lab reports for accuracy, completeness, and closeness of their predictions to the results of their experimentation.

Elaboration

Participants' choice:

Choose one of the following activities to complete this lesson:

  1. Create a graph that shows the amount of each liquid that the penny could hold.
  2. Calculate how many milliliters of each liquid you were able to get onto the penny. HINT: Base your calculations on the number of drops in one milliliter. Be sure to show your math.

Assessment: Check participants' reports for accuracy and completeness.

Elaboration and Classroom Implementation

Have participants design an experiment (see Lesson Implementation Plan) to collect data on the following (if possible observe participants in designing the experiments):

  • Determine the distance of water travel in a white carnation or celery in the sun
  • Determine the distance of water travel in a white carnation or celery in the refrigerator
  • Determine the distance of water travel in a white carnation or celery in the room

OR

  • Determine the difference in using a wet versus a dry string to transfer water from one cup or glass to another using a string. (Place one beaker ¾ full of water on the side of a book and an empty beaker on the other side. Wet the string in the first beaker and place one end in the same. Place the other end of the string in second beaker. Holding the first beaker up slowly, pour water on the string into second beaker. Repeat using a dry string)

Pose the questions:

  • Will the celery and carnation react differently? Explain why or why not.
  • Will there be a difference in results using a wet versus a dry string?

Have participants provide everyday example(s) of the experiment.


Rationale

Effective teaching is at the heart of science education, which is why the science teaching standards are presented first. Good teachers of science create environments in which they and their students work together as active learners. They have continually expanding theoretical and practical knowledge about science, learning, and science teaching. They use assessments of students and of their own teaching to plan and conduct their teaching. They build strong, sustained relationships with students that are grounded in their knowledge of students' similarities and differences. And they are active as members of science-learning communities.

As envisioned by the standards, teachers partake in development experiences appropriate to their status as professionals. Beginning with pre-service experiences and continuing as an integral part of teachers' professional practice, teachers have opportunities to work with master educators and reflect on teaching practice. They learn how students with diverse interests, abilities, and experiences make sense of scientific ideas and what a teacher does to support and guide all students. They study and engage in research on science teaching and learning, regularly sharing with colleagues what they have learned. They become students of the discipline of teaching.


Science Standards

Content, Technology, and Professional Development:

NSES Content Standard A: Science as Inquiry: As a result of activities, in grades 5-8, all students should develop

  • abilities necessary to do scientific inquiry
  • understandings about scientific inquiry

NSES Content Standard B: Physical Science: As a result of activities, in grades 5-8, all students should develop an understanding of

  • properties and changes of properties in matter

NSES PROFESSIONAL DEVELOPMENT STANDARD A: Professional development for teachers of science requires learning essential science content through the perspectives and methods of inquiry.

NSES PROFESSIONAL DEVELOPMENT STANDARD B: Professional development for teachers of science requires integrating knowledge of science, learning, pedagogy, and students; it also requires applying that knowledge to science teaching.

NSES PROFESSIONAL DEVELOPMENT STANDARD C: Professional development for teachers of science requires building understanding and ability for lifelong learning.


Best Teaching Practices

  • Observation
  • Inquiry
  • Hands-on/Minds-on

Time Frame

2-3 hours depending on the topics based on variations in the procedures selected by the facilitator


Preparation

The total cost for running a session for about 30 to 32 participants would be about $10.00. The cost will be less if some of the materials can be borrowed from existing science classrooms.

  1. Go to google.com and click on images. Search individually for:
    • a bubble
    • a piece of bubble gum stuck to the bottom of a shoe
    • a gecko sticking to a wall, a raindrop
    • a roll of Scotch tape
    • a dripping faucet

Print each out individually on 8 ½ X 11 sheet of paper. Be careful when printing since the margins on the paper may not agree with what you see on the screen. The other option is to project the material rather than provide hard copies for each participant.

  1. Prepare materials for each group of three or four teachers. Mix the following:
    • Tap water with soap
    • Blue food coloring with tap water
    • Red food coloring with soapy water
    • Green food coloring with rubbing alcohol
  2. Gather remaining materials and place at each table for participants.
  3. Notify participants in advance to bring curriculum guide, textbook, or other science resources. From these materials they can derive and use science lessons to help to facilitate their production of an implementation plan.

Safety

Be sure that participants are following the procedures. Have towels available for spills. Participants should not eat or drink anything in the lab. Clean up all materials and dispose of liquids. Flush water and alcohol down drain; run lots of water afterwards to clear drain.


Assessment

Pose the following situation. Ask participants to make predictions and explain their predictions using their understanding of adhesion and cohesion.

Gently place a drop of water on a piece of foil. If you took a toothpick and scratched through the drop, what do you think will happen to the drop? Use your understanding of cohesion and adhesion to explain your prediction.

Gently place a drop of water on a piece of foil. If you dip the end of a toothpick into some detergent and scratched through the drop, what do you think will happen to the drop? Use your understanding of cohesion and adhesion to explain your prediction.

Gently place a paper towel on top of a drop of water on a piece of foil. What do you think will happen to the drop? Use your understanding of cohesion and adhesion to explain your prediction.


Explanation of Science

Some molecules, such as water, are polar in nature with a permanent dipole moment. A dipole moment means that the molecule has a more negative end (the oxygen atom) and a more positive end (the hydrogen atoms). The negative end of these molecules will attract the positive end of nearby molecules.

Cohesion is when the molecules that are attracted are the same type of molecules. In other words, cohesion is the force of attraction that holds these substances together. The cohesive forces are responsible for the surface tension of a liquid (water beading up on a surface). The prefix 'co' means together - the molecules are pulled together. Some materials, such as soap, will reduce the surface tension of water.

Adhesion is the term to describe the interactions between different types of molecules, for example, water with a paper towel. In other words, adhesion is the force of attraction between different substances. The prefix 'ad' means towards, to, or near.


Handouts

None available for this module.


Extensions

Have participants float an empty berry basket on top of water in a container. Discuss that even with the holes in it, it will float. Participants explain why. (ASSESSMENT.)

Have participants put water on a glass slide, and sprinkle a little black pepper on the water; it will float. Put a little liquid soap on their finger and touch the pepper-covered water. The surface tension will break where the soap touches it and pull the pepper away. Participants explain why. (ASSESSMENT.)


Lesson Implementation Template

Download Lesson Implementation Template: Word Document or PDF File


Equity

Issues to be considered are the following: Arrange seating for all participants to be actively engaged in the training and discussions. Provide copies of graphs for ease of comparison. Group participants with diversity in mind.


Resources

N/A for this module.


References

http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html - Index to HyperPhysics

http://www.exploratorium.edu/xref/phenomena/surface_tension.html - Exploratorium exhibit phenomenon