| |
 |
Activity 1: Grades 5-8
Weighing In |
|
As
you observed in "Getting
to Know Us", researchers have developed a floor that
allows them to identify and track individuals by their weight.
The floor includes sensors that trace the impact of footsteps.
Entered into a database, the collected impacts can be used
to construct a specific individual's movement history. This
"intelligent floor" is so precise that it can detect when
you've added a cup of milk to a recipe!
How
do YOU measure quantities such as fluid ounces? Most likely
you use a measuring cup or a similar device that measures
volume. Things are about to change. The following activity
will allow you to emulate the weighing technique associated
with an intelligent floor. It will also examine the difference
between "accuracy" and "precision," important considerations
when using any measuring technique.
The "accuracy" of a device describes how close its readings
are to the actual value. If a scale measures the weight of
a 5-pound sack as five pounds, it is very accurate. If it
produces a reading of 6 pounds, it is less accurate. The "precision"
of a device refers to the repeatability of the measure. Will
the scale always give a reading of precisely 5 pounds? Will
it produce a narrow range of values, thus making it "high
precision"? Or will it present a wide range of values associated
with "poor precision"?
|
|
|
|
|
|
This activity page will offer:
-
Insight into the relationship between volume and mass
- An
opportunity to differentiate between accuracy and precision
- An
arena for creating a strategy to measure volume
- A
chance to emulate the action of the pressure sensitive floor in
measuring quantities
MATERIALS
- Bathroom
scale (digital works best)
- Measuring
cup
- Water
- 2-liter
container
- 5-pound
bag of rice
- Clean
kitchen bowl
Teachers:
Please see the
Teacher's Note on the
Answers Page
PROCEDURE
- Identify the bathroom scale that you will use in this activity.
Is the weighing device digital or analog? Does the scale include
any information about the reliability of its measure (such as
+/- .2 pounds)?
- Stand on the scale. Note and record your weight shown on the
scale display. Step off the scale. Weigh yourself two more times
and average the three readings.
- Place an unopened five-pound bag of rice on the scale. Determine
and record the weight of this bag and contents as measured by
the scale. Reweigh this bag twice more and average the three readings.
- Make a prediction. Suppose you were to stand on the scale holding
the bag of rice. How much weight should the scale read?
- Weigh yourself with the 5-pound bag. Was your prediction correct?
Why or why not? Explain any differences.
- Using the value you obtained in step 3, determine the approximate
weight of one fluid ounce of rice. (Divide the total weight of
package by its volume in ounces)
- Develop a strategy that you could use to remove twenty fluid
ounces of rice from the bag without using a volumetric tool. Then,
using clean utensils and a bowl, test your strategy. Check your
results with a measuring cup. Did your strategy work? Explain.
When you are finished, return the rice to its bag.
- Fill a 2-liter container with water. Obtain and record the weight
of the water-filled container.
- Apply the strategy you developed in step 7, to measure out 0.5
liters from this 2-liter container. By what percentage must the
container's original weight be decreased in order to remove 0.5
liters? When you are done, use a measuring cup to test the accuracy
of your procedure.
Questions
- Why did you need to repeat the weighing measurements?
- Would the weight of the container in which the rice or water
is stored affect the accuracy or precision of the measurement?
Explain.
- Make a prediction. How would using molasses instead of water
affect the weight of the measured and removed liquid?
EXTENSIONS
High Heel Pressure
In
most schools, spiked high-heeled shoes are not allowed on a wooden
gym floor. The reason for this ban has to do with science - not
sociology! When you stand on a mostly flat sole, your body weight
is distributed over the entire area of the contact surface. So if
you weighed 150 pounds and you stood on one foot that contacted
30 square inches of surface, you'd produce a pressure of about 5
pounds/square inch. Suppose you only made contact with the spike
of a high-heeled shoe. How would this effect pressure? Explain.
Use a ruler, scale and a variety of shoes with various heel contours
to determine variance in a person's walking pressure.
Between You and a Door
Imagine a "smart door" like the one you saw in the program, only
one with an attitude. How might this device reply to different individuals?
Would it show a bias in its communication regarding gender, profession,
or a visitor's motives? Think about it. Then apply your creative
writing skills to creating a humorous essay about an hour in the
life of this communication interface.
Intelligent
Elevator
How might the footstep profiles captured by an "intelligent floor"
be used to improve elevator service? Should this intelligent floor
be placed inside or outside of the elevator, or both? Explain the
benefits of each approach. Could it address pranksters who might
press all of the floor buttons? If so, how? How might the floor
address a car that was overloaded?
Freedom
of Movement
The ability to track individuals on a floor might be interpreted
as a challenge to a person's right to anonymity. Do you think this
violates a person's rights as guaranteed by the constitution? Should
a person need to sign a release in order for his/her footstep profile
to be recorded? Suppose you were a lawyer who challenged the legality
of this process? How would you present your case?
WEB
CONNECTION
Accuracy
and Precision
http://www.flatsurv.com/accuprec.htm
Learn more about accuracy and precision in measurement.
Self-Organizing
Elevators
http://www.halfbakery.com/idea/Self-Organizing_20Elevators
A fun and informative site that describes intelligent floors and
uses in elevator environments.
The
Smart Floor
http://citeseer.nj.nec.com/271128.html
This article describes the use of a smart floor as a means of tracking
individuals by footstep profiles.
The
activities in this guide were contributed by Michael DiSpezio, a
Massachusetts-based science writer and author of "Critical Thinking
Puzzles" and "Awesome Experiments in Light & Sound" (Sterling Publishing
Co., NY).
Academic Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools, Wayland,
MA
Suzanne Panico, Science Teacher Mentor, Cambridge Public Schools,
Cambridge, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland,
MA
|
