this procedure, students should develop their own approach to the
weighing technique that was observed in this SAF segment. Your role
as instructor is to facilitate this process as the students engage
higher thinking skills to attain this goal. Guide them, but do not
tell them how this is accomplished. The desired outcome should be
a volumetric weighing technique that is based upon differences in
the observed weight of both the "weigher" and the item being weighed.
Make a prediction. Suppose you were to stand on the scale holding
the bag of rice. How much weight should the scale read?
(Answers will vary be this should be the sum of the student's
weight and the weight of the rice bag.)
Weigh yourself with the 5-pound bag. Was your prediction correct?
Why or why not? Explain any differences.
(Scale may not retain its accuracy over a range in weight measurements).
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?
- Why did you need to repeat the weighing measurements?
(In order to assure repeatability, the weighing was repeated.
This repeatability was a measurement of the precision of the weighing
device. The final average was a more reliable number than any
of the individual values.)
- Would the weight of the container in which the rice or water
is stored affect the accuracy or precision of the measurement?
(The weight of the container will offset the recorded value
by a small, fixed value. This affects the accuracy of the measures.
If we assume that the container's weight does not interfere with
the scale's mechanism, we should observe the same repeatability
of measure (precision) in all readings.)
- Make a prediction. How would using molasses instead of water
affect the weight of the measured and removed liquid?
(Since molasses is a thick, sugar-rich solution, the observed
weight measurements will be greater.)
High Heel Pressure
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.
heel's smaller contact area will assume the entire weight. Therefore,
this single but small area contact point would produce a large increase
in pressure - often strong enough to produce "dings" in the wooden