How Do We Measure Forces at the Nanoscale Level? 1 © 2009 McREL Physical Science Lesson 7 How Do We Measure Forces at the Nanoscale Level? Investigating Static Forces in Nature: The Mystery of the Gecko

How Do We Measure Forces at the Nanoscale Level? 2 © 2009 McREL Probes What are some instruments (probes) you have used in previous science classes?

How Do We Measure Forces at the Nanoscale Level? 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 cm = 0.4 cm) Image 7.5

How Do We Measure Forces at the Nanoscale Level? 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. Image 7.6

How Do We Measure Forces at the Nanoscale Level? 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 tip cantilever Image 7.7

How Do We Measure Forces at the Nanoscale Level? 6 © 2009 McREL Comparison of AFM and Box Model AFMBox Model What characteristic is measured by the probe? How is the characteristic measured by the probe?

How Do We Measure Forces at the Nanoscale Level? 7 © 2009 McREL Modeling a Gecko Seta Question: How do gecko spatulas of a seta affect the amount of surface contact? One gecko setaMany spatulas on the top of one gecko seta Image 7.9Image 7.10

How Do We Measure Forces at the Nanoscale Level? 8 © 2009 McREL Possible Setup Image 7.11Image 7.12Image 7.13Image 7.14

How Do We Measure Forces at the Nanoscale Level? 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

How Do We Measure Forces at the Nanoscale Level? 10 © 2009 McREL Spatulas on Surfaces Image 7.16 Image 7.17

How Do We Measure Forces at the Nanoscale Level? 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?

How Do We Measure Forces at the Nanoscale Level? 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

How Do We Measure Forces at the Nanoscale Level? 13 © 2009 McREL Typical Lateral Force Curve Image 7.20

How Do We Measure Forces at the Nanoscale Level? 14 © 2009 McREL Adhesion Hypothesis Dense arrays of “spatulas” conform to match topography of an opposing surface. Tip of one gecko setaImage 7.21 Image 7.22

How Do We Measure Forces at the Nanoscale Level? 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?

How Do We Measure Forces at the Nanoscale Level? 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: Visible Force: Gravity Tools: Eyes 3. What Are Your Ideas About Small Sizes? Scale: Visible/Invisible Dominant Force: Varies Tools: Eyes, Instruments 1. How Can a Gecko Walk on a Ceiling? Scale: Visible Dominant Force: Gravity Tools: Eye 5. What Types of Forces Can Hold Objects Together? Scale: Visible/Invisible Dominant Force: Gravity Tools: Eyes and Hands 4.What Do We Learn When We Look More Closely? Scale: Invisible Dominant 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?