Download AFMActivity2015 - ScholarWorks@UMass Amherst

A Fine Measurement Machine
1
STEM ED/CHM Nanotechnology at UMass Amherst
A Fine Measurement Machine
The diagrams below illustrate how sliding a thin object under one end of a lever
changes the direction of a reflected beam of light.
paper
Laser Pointer
Hanging mass
mirror
Lever support
The reflected light beam now reaches
a different point on the paper.
Two questions to answer before you start the activity
Question 1: Why would the point of light reach a different position on the paper
when an object causes the lever to move?
Question 2: How could this lever mechanism be used to measure the thickness of an
object with an unknown thickness?
A Fine Measurement Machine
2
There are a number of tasks for team members.
1. Safety Alert: Make sure that the laser beam is not exposed to anyone.
2. Maintain the stability and position of the lever mechanism.
3. Coordinate movements with other those of other groups so that each group’s
reflected beam of light reaches a sheet of paper on a wall.
4. Measure the position of the reflected beam of light on a sheet of paper.
Set up a Measurement Machine: (Note: These directions are specific for
equipment available during the STEM ED/CHM Nanotechnology Summer Institute)
1. Put a knife-edge clamp on top of a meterstick support.
2. Put a meterstick through the opening in the knife-edge clamp so that the
lever has a long arm and a short arm. Tighten the knob on the clamp.
3. Double-sided tape can be used to secure the mirror to the end of the longer
arm of the lever. Please remove the tape at the end of the activity.
4. Put another knife-edge clamp somewhere on the shorter arm of the lever.
5. Attach a wire mass hanger to that knife-edge clamp.
6. Attach a mass to the wire mass hanger.
7. Adjust the position of the mass and/or the size of the mass so that the
lever is very slightly out of balance. The end of the long arm of the lever
should exert a very small amount of downward force on an object.
8. Move a tripod stand close to the end of the lever that has a hanging mass.
9. Attach a laser pointer to a clamp at the top of the tripod stand.
10. Turn on the laser and aim the laser beam in the direction of the mirror. You
can use a piece of paper to see where the laser beam strikes the mirror.
11. Observe where the reflected beam of light reaches a wall.
12. Use painters tape to attach a sheet of paper to the wall so you can measure
the positions of the dots of laser light on the wall. Do not use tape that will
be hard to remove from the wall.
13. Adjust the distance of the tripod stand from the mirror and/or the tilt of
the laser clamp so the beam of light reflected from the mirror reaches the
sheet of paper on a wall.
A Fine Measurement Machine
3
Calibrate the Measurement Machine
Determine the mathematical relationship between the movement of the point
of light on a wall and the movement of the lever arm when using calibrating objects.
Examples of Calibrating Objects
 You can use sheets of paper for a duplicating machine. Measure the

thickness of the entire ream of paper with a metric ruler and then calculate
the thickness of one sheet of paper.
You can use shims with a known thickness that include: Pink = 0.4 mm,
Brown = 0.25 mm, Clear = 0.19 mm and Green = 0.08 mm
The Calibrating Procedure
1. The mirror end of the lever should rest gently on the table and the
reflected beam of light should be somewhere a sheet of paper on the wall.
2. Mark the location of the laser light on the sheet of paper on a wall when the
mirror end of the meterstick is resting on the table. Note: The beam of
light will not be a point of light on the paper. Thus, you will need to decide
how you will mark the location of the reflected beam of light.
3. A person in the group should slide a calibrating object (such as a shim or a
number of sheets of paper) under the mirror end of the ruler.
4. Measure and record the change in the location of the point of light on the
sheet of paper.
5. Slowly remove the calibrating object from underneath the mirror end of the
meterstick.
6. Determine if the position of the reflected beam of light returns to the
same location as in Step 2.
7. Move the calibrating object under the mirror end of the meterstick a
second time to recalibrate the fine measurement machine.
8. Repeat the calibration process with several different objects of known
thicknesses.
Question 3: Why should multiple trials be conducted with each calibrating object?
Question 4: How can a graph be used to determine the thickness of a new set of
objects?
Question 5: What are some possible sources of error during the calibration
process?
The Measurement Challenge
You will be given some different shims or other object. Develop a strategy to
determine the thickness of the new shims or sheets of paper.
A Fine Measurement Machine
4
Question 6: How accurately were you able to measure the thicknesses?
You can replace the sheet of paper with a mirror and reflect the laser beam to
another location. Try that if time permits.
Question 7: How did increasing the distance the reflected beam of light travel
affect the measurement process?
Question 8: A precise instrument obtains the same value each time the instrument
is used. How could you improve the precision of your measurement machine?
An Optional Activity: If time permits, attach a probe to the lever mechanism.
Question 9: What adjustments would have to be made to use the lever mechanism
when a probe is attached in order to measure the thickness of an object?
Question 10: How would you design a support for a flexible cantilever shown below?