5.1 Investigating Static Forces in Nature: The Mystery of the Gecko

Activity: What Sticks?

Slide 3

Station	Materials/Suggested Procedure	Which Objects Stick Together?	How They Stick Together (In Your Own Words)	Adhesion Method (Circle Your Answer)
1	Magnets, Paperclips, Plastic Transparency Place paperclip on top of the plastic transparency Slowly tilt transparency on an angle until the paper clip begins to slide Repeat by clipping the paperclip to the transparency Repeat with the magnet and plastic transparency			Friction Suction Micro-Interlocking Magnetic Static Electricity Capillary Wet Adhesion Electrical
2	Suction Cups, Plastic Transparency Stick the suction cup to the plastic transparency and turn it upside down			Friction Suction Micro-Interlocking Magnetic Static Electricity Capillary Wet Adhesion Electrical
3	Fur or Wool, Balloon, and Plastic Transparency Rub the balloon with the fur and stick the balloon to the plastic transparency and turn it upside down			Friction Suction Micro-Interlocking Magnetic Static Electricity Capillary Wet Adhesion Electrical
4	Beaker of Water, Paper Towel, Plastic Transparency Place a 5cm. strip of paper towel into water and stick the paper towel strip to the plastic transparency and turn it upside down			Friction Suction Micro-Interlocking Magnetic Static Electricity Capillary Wet Adhesion Electrical
5	Washers, Velcro®, Plastic Transparency First, attach the Velcro® to the plastic transparency and turn it upside down. Then, attach the Velcro® to both sides of another piece of Velcro® Turn each upside down.			Friction Suction Micro-Interlocking Magnetic Static Electricity Capillary Wet Adhesion Electrical
6	Transparent Tape and Plastic Transparency Place the tape on the plastic transparency and turn it upside down			Friction Suction Micro-Interlocking Magnetic Static Electricity Capillary Wet Adhesion Electrical
Additional Station 7 (Optional)
Additional Station 8 (Optional)
Additional Station 9 (Optional)

1. Choose one pair of objects that stuck together. Describe factors (variables) that affect how well those two objects stick together.

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2. Describe an adhesive in your own words. What are the properties that make it work?

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3. Which factors or variables are testable and which are not?

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4. Describe how you made your observations in today’s lesson:

a. What senses/tools did you use?

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b. What observations of forces were at the visible scale?

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c. What dominant forces did you observe?

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d. What are other forces that you observed that may be at the invisible scale?

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Homework: Based on the factors that you determined are testable, write a plan to determine how a factor could be tested. Write it as an experimental procedure on a separate sheet of paper.

Slide 7: Adhesion Methods Debrief Chart

Directions: Based on your exploration, list examples of each type of adhesion method in the chart on the next page. Complete the first three columns on your own based on your previous work in the stations.

Then, within a small group, you will investigate some research findings on a specific adhesion method and consider whether it is a possible method for gecko adhesion. Your group will write down notes on a separate Adhesion Methods Student Handout and present this information to the rest of the class.

During the class presentations, return to the chart to complete the remaining columns.

Method	Definition (In Your Own Words)	Drawing That Describes the Method	Examples from Experiment Stations (Slide 7)	Is this method a possible answer to the gecko mystery? (Yes or No)	Why or Why Not?
Mechanical Force: Friction
Mechanical Force: Air pressure (suction cups)
Mechanical Force: Microinterlocking
Intermolecular Force: Magnetic
Intermolecular Force: Static Electricity
Intermolecular Force: Electrical (Capillary Wet Adhesion)
Intermolecular Force: Electrical (Tape)

5. Which method is the most likely one that explains the gecko problem? Why?

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Adhesion Methods Student Handout

Each team will be assigned to one of the seven adhesion methods indicated below. Read the information about each one, define it in your own words, draw a picture of the method, and then answer the question(s) for your assigned adhesion method.

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Mechanical Force: Friction

Friction	Friction In Your Own Words	Drawing of Friction
Friction is a force that opposes the lateral (side-to-side) motion of two surfaces that are in contact. While there is friction between the gecko’s foot and the surface, is this the method by which it adheres?

Questions

Based on this new information, do you think friction is a possible method for gecko adhesion?

Why or why not?

Adhesion Methods Student Handout

Each team will be assigned to one of the seven adhesion methods indicated below. Read the information about each one, define it in your own words, draw a picture of the method, and then answer the question(s) for your assigned adhesion method.

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Intermolecular Force: Static Electricity

Static Electricity	Static Electricity In Your Own Words	Drawing of Static Electricity
Static electricity involves the buildup of charge in objects due to contact between insulators. These charges are generally built up through the flow of electrons from one object to another causing one object to become positively charged and the other object to be negative. Positively charged objects and negatively charged objects are attracted to each other. The gecko’s adhesion force is the same whether the surface is charged or uncharged. The gecko’s adhesion force is also the same whether the air is charged or uncharged.

Questions

Based on this new information, do you think static electricity is a possible method for gecko adhesion?

Why or why not?

Adhesion Methods Student Handout

Each team will be assigned to one of the seven adhesion methods indicated below. Read the information about each one, define it in your own words, draw a picture of the method, and then answer the question(s) for your assigned adhesion method.

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Intermolecular Force: Capillary Wet Adhesion

Capillary Wet Adhesion (Water)	Capillary Wet Adhesion (Water) In Your Own Words	Drawing of Capillary Wet Adhesion (Water)
Water molecules are not only attracted to each other, but to any molecule with positive or negative charges. When you place paper from a straw partially into a glass of water, the water will “climb” up the fibers of the straw paper because the water molecules are attracted to the cellulose fibers in the straw paper. Observations made with geckos indicate that there is no wet trail left behind when geckos walk on a surface. Skin glands are not present on gecko feet—the foot does not have a way to secrete any substance.

Questions

Based on this new information, do you think capillary wet adhesion is a possible method for gecko adhesion?

Why or why not?

Adhesion Methods Student Handout

Each team will be assigned to one of the seven adhesion methods indicated below. Read the information about each one, define it in your own words, draw a picture of the method, and then answer the question(s) for your assigned adhesion method.

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Mechanical Force: Air Pressure (Suction Cups)

Air Pressure (Suction Cups)	Air Pressure In Your Own Words	Drawing of Air Pressure
Air pressure is the force from molecules of air hitting a surface. A suction cup is a device made of either plastic or rubber that sticks to smooth surfaces. In a suction cup, a partial vacuum (region of low pressure) is created so that there are fewer molecules than before the suction cup was applied to a surface. Once the suction cup is pressed onto a surface, the air pressure inside the cup is greatly reduced compared with the higher pressure from the surrounding air. This forces the suction cup to stick to the surface. Gecko force experiments indicate that the same force measurements have occurred when the gecko setae are tested in a vacuum (no air pressure) as in regular air.

Questions

Based on this new information, do you think suction is a possible method for gecko adhesion?

Why or why not?

Adhesion Methods Student Handout

Each team will be assigned to one of the seven adhesion methods indicated below. Read the information about each one, define it in your own words, draw a picture of the method, and then answer the question(s) for your assigned adhesion method.

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Mechanical Force: Micro-Interlocking

Micro-Interlocking	Micro-Interlocking In Your Own Words	Drawing of Micro-Interlocking
Two materials may be mechanically interlocked. One object is linked, hooked, or anchored to another object. At the macroscopic scale, examples include: a zipper, sewing two pieces of cloth with a thread, and two pieces of Velcro® that are attached. For the gecko, no interlocking has been observed. In fact, force measurements have been the same amount per unit area for different opposing materials.

Questions

Based on this new information, do you think micro-interlocking is a possible method for gecko adhesion?

Why or why not?

Adhesion Methods Student Handout

Each team will be assigned to one of the seven adhesion methods indicated below. Read the information about each one, define it in your own words, draw a picture of the method, and then answer the question(s) for your assigned adhesion method.

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Intermolecular Forces: Electrical (Tape)

Intermolecular Forces: Electrical (Tape)	Intermolecular Forces: Electrical (Tape) Forces In Your Own Words	Drawing of Intermolecular Forces: Electrical (Tape)
Intermolecular forces are weak electrical forces between molecules that are very close together. For these forces to adhere an object to another, the object must be compliant. Transparent tape has two layers. The adhesive layer has a structure that at the molecular level has properties similar to a liquid. The other layer has properties more like a solid. The adhesion layer of the tape makes compliant contact with the surface so that more intermolecular electrical attractions can occur. For this method to be considered a possibility for gecko adhesion, each seta must have properties similar to the tape. This would then allow the seta to make compliant contact with the opposing surface.

Questions

Based on this new information, do you think intermolecular forces are a possible method for gecko adhesion?

Why or why not?

Adhesion Methods Student Handout

Each team will be assigned to one of the seven adhesion methods indicated below. Read the information about each one, define it in your own words, draw a picture of the method, and then answer the question(s) for your assigned adhesion method.

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Intermolecular Force: Magnetic

Magnetic	Magnetic In Your Own Words	Drawing of Magnetic
A magnet is an object with a magnetic field. A “hard” magnet is one which stays magnetized for a long time. A “soft” magnet is one which loses its magnetic properties. Opposite poles of magnets attract.

Questions

Based on this new information, do you think magnetic force is a possible method for gecko adhesion?

Why or why not?

Investigating Static Forces in Nature: The Mystery of the Gecko

Adhesion Methods Student Handout

© 2009 McREL