how do we measure forces at the nanoscale level? 1 © 2009 mcrel physical science lesson 7 how do we...

How Do We Measure Forces at the Nanoscale Level?

1© 2009 McREL

Physical Science

Lesson 7


Investigating Static Forces in Nature:

The Mystery of the Gecko


2© 2009 McREL

Probes

What are some instruments (probes) you have used in previous science classes?


3© 2009 McREL

How to Measure the Height of an Object With a Probe

• Insert the probe in an area of the box with no object (9.0 cm)• Insert the probe in an area of the box with the object (8.6 cm)• The height of the object at that point is the difference

(9.0 cm - 8.6 cm = 0.4 cm)

Image 7.5


4© 2009 McREL

Making a 3-D Representation

Based on the height data gathered from your probing activity, use a spreadsheet program to make a 3-D representation of the unseen surface.

38

52

2 44

62

25

5 3 2 2

4 3 2 2

0

1

2

3

4

5

6

5-6

4-5

3-4

2-3

1-2

0-1

Image 7.6


5© 2009 McREL

Atomic Force Microscope

Image 7.8

AFM measures/images topography of surface: deflection of cantilever proportional to height of surface feature

sharp tipcantilever

Image 7.7


6© 2009 McREL

Comparison of AFM and Box Model

AFM Box Model

What characteristic is measured by the probe?

How is the characteristic measured by the probe?


7© 2009 McREL

Modeling a Gecko Seta

Question: How do gecko spatulas of a seta affect the amount of surface contact?

(d) spatula-shaped tips (~0.2m)

(d)

1 m

(d) spatula-shaped tips (~0.2m)

(d)

1 m

One gecko seta Many spatulas on the top of one gecko seta

Image 7.9 Image 7.10


8© 2009 McREL

Possible Setup

Image 7.11 Image 7.12 Image 7.13 Image 7.14


9© 2009 McREL

Compliant Surfaces

If one or both surfaces are compliant :

Image 7.15

Soft – Transparent Tape

Hard – Desk Top

apparent contact area real contact area


10© 2009 McREL

Spatulas on Surfaces

Image 7.16

Image 7.17


11© 2009 McREL

Journal Prompts

1. Look back at your previous methods (from lessons 5) as to how the gecko adheres to a wall. Are there some that you could eliminate because of the new information you now have? Are there any new interpretations you would add?

2. What new questions do you have about surface-to-surface interactions?


12© 2009 McREL

Measuring Tiny Forces

How could the force between one gecko seta and a surface be measured?

Micro-Electro-Mechanical System (MEMS) Probe

Single Gecko Seta

Cantilever

Seta slides on the surface and builds up larger adhesion forces

Pull Direction

Image 7.19Image 7.18


14© 2009 McREL

Adhesion Hypothesis Dense arrays of

“spatulas” conform to match topography of an opposing surface.

Tip of one gecko seta

Image 7.21

Image 7.22


15© 2009 McREL

Making Connections

1. How are AFM and the MEMS devices used to help understand gecko adhesion?

2. What do we now know about the amount of force between a single seta and a surface?

3. How does this new information help us understand the adhesion method for the gecko?

4. What should we explore next?


16© 2009 McREL

Flow Chart

7. How Do We Measure Forces at the Nano Level?

Scale: Visible and Invisible

Dominant Force: Extremely Small, Large in Number

Tools: Atomic Force Microscope

8. How Can a Gecko Walk on a Ceiling?

2. What Do We Mean When We Speak About Surfaces in Contact?

Scale: VisibleForce: GravityTools: Eyes

3. What Are Your Ideas About Small Sizes?

Scale: Visible/InvisibleDominant Force: VariesTools: Eyes, Instruments

1. How Can a Gecko Walk on a Ceiling?

Scale: VisibleDominant Force: GravityTools: Eye

5. What Types of Forces Can Hold Objects Together?

Scale: Visible/InvisibleDominant Force: GravityTools: Eyes and Hands

4. What Do We Learn When We Look More Closely?

Scale: InvisibleDominant Force:

Extremely Small, Large in Number

Tools: Special instruments (scanning tunneling microscope)

6. How MUCH Force Is Needed to Make an Object Stick? What Factors Affect the STRENGTH of Force Acting?

how do we measure forces at the nanoscale level? 1 © 2009 mcrel physical science lesson 7 how do we...

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