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Slide 1

Draw one example of balanced forces and one example of unbalanced forces from your classroom in the boxes below.Use arrows to indicate the direction of the forces. Draw large arrows for large forces and small arrows for small forces.

Example of balanced Force Example of Unbalanced Force

Slide 2

When an object is sticking to a ceiling, what are the two forces that come into play? In order for the shoe to remain on the ceiling, what must be true about these forces?

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Slide 3

Weight of Ant = 0.00004 \;\mathrm{Newtons}

Draw and label arrows representing the forces on the ant that is on the ceiling on the diagram below. Then, calculate the force required for each ant foot. (Note: Divide total force by six.) Be sure to show correct units.

We are assuming in this problem that the total force required is equally divided among the six ant feet, and that ONLY the contact between feet and ceiling gives rise to the force.

Slide 4

Imagine an object that is larger in every dimension and whose mass and volume is ten times larger than an ant.

How many “ant feet” would it take for this imaginary object to remain adhered to the ceiling? Show your calculations below. Be sure to show correct units.

Slide 5

Now, apply this calculation for the Tokay Gecko, which has an average weight of 2.2 Newtons. How many “ant feet” would it take for the gecko to remain adhered to the ceiling? Be sure to show correct units.

Write a statement and/or draw pictures that describe the relationship between size (mass) and weight and, therefore, adhesive forces required for an animal to remain on a ceiling.

Slide 8

How could one measure the amount of “stickiness” of a piece of tape on a tabletop?

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The fundamental assumption in testing for adhesion is that the force that holds the tape in place is the same as the force required to remove it. This is NOT true. The force required to remove the tape is actually a lot greater. Much of the separation force is going to extend the adhesive prior to separation and to bend the backing. However, it is the most practical form of adhesion testing available.”

Adapted from Johnston, J. (2003). Pressure sensitive adhesive tapes. Pressure Sensitive Tape Council. Northbrook, Illinois, page 154.

Experiment: Tape Pull

Question: How does the amount of dirt affect the amount of force required to lift a piece of tape from the tabletop?

Materials: transparent tape, duct tape, spring scale, hole punch, metric ruler, protractor

Procedure Practice:

Set up your testing apparatus as shown below.

Transparent tape and hole for spring scale

1. Place some transparent tape onto a desk or lab table so that half of the tape is hanging off the edge.

2. Measure the amount of surface area of tabletop that the tape touches (Area = Length times Width).

Area =

3. Use duct tape to make a reinforced end on the tape that is not touching the tabletop.

4. Use the hole-punch to make a hole through the duct tape and the transparent tape.

5. Place the hook end of the spring scale into the hole.

6. Practice pulling the spring scale to measure the amount of force needed to remove the tape from the tabletop.

7. Record your observations from this practice below.

Procedure Experiment:

1. Hypothesis: Write a hypothesis below:

If the amount of dirt on the tape ____________________ (increases or decreases), then the force required to remove the tape _____________________ (increases or decreases).

2. Based on your practice trials:

A. What was the independent variable (variable you were testing)?

B. What was the dependent variable (variable being measured)?

3. Write your procedure (in the box below) for testing the force needed to remove transparent tape from the tabletop with varying amounts of dirt. Be sure to include the proposed amount of dirt for the experiment. How will you vary the amount of dirt? (e.g., clean, somewhat dirty, and very dirty).

4. Remember that you are measuring the effect that the amount of dirt has on the force needed to remove the transparent tape. All other variables should be held constant including the angle of pull, the amount of tape that is in contact with the tabletop, etc. What other variables should be held constant?

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5. Record your data in the box below. You should test the same amount of dirt for at least three trials and then determine the average force (in Newtons) that it took to remove the tape from the tabletop. Make sure you make both quantitative (force measurements) and qualitative (notes and drawings) for your data tables.

Analysis/Interpretation

6. Based on the information in your data table, write an answer to the original research question above.

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

a. What tools did you use?

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b. Were your observations at the visible or invisible scale?

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c. What is the dominant force at this scale?

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Graph Your Results Using a Bar Graph

Conclusions

8. Did your data support your hypothesis? Explain.

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Investigating Static Forces in Nature: The Mystery of the Gecko

Lesson 6: How MUCH Force is Needed to Make an Object Stick?

Student Journal

© 2009 McREL

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Feb 23, 2012

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Aug 30, 2014
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