Workshop 1 Web Highlights
"Size vs. Mass"
You show a young child two arrangements of three blocks. One is
stacked vertically, the other arranged horizontally. If you ask
the child, "Which is 'more'?," they would likely point to the taller
stack. Older children and even some adults are confused with the
ideas of size, surface area, volume, mass, weight and density since
most of the terms relate to "how much" in some way.
The students doing the "Asteroid!" activity have a similar problem
with some of these terms. If we were talking about the size of a
rectangular block, we might think of the length, width or height
of the block or even its surface area or volume. For spherical objects
such as the students are using we might relate the size of the ball
to its radius or diameter. Two balls of the same size could have
very different masses if one was made from lead and the other from
"Units of Measurement"
In the United States we are familiar with the English system of
measurement units: inch, foot, mile, pound, gallon, second, minute
and hour. Most other countries use the metric system that is actually
much easier to understand. Scientists report their findings using
"The Fundamental Units of the International System" or SI units.
While they report in SI units, their actual measurements are made
in whatever units are most convenient and converted later.
The students in the classrooms we will see in this series use the
metric system for their measurements and we will too! Since most
of the objects they are working with are hand size, lengths will
usually be measured in centimeters (cm), mass in grams (g) and time
in seconds (s). To measure a force we will always use Newtons (N).
One Newton is equivalent to about 0.225 pounds, or about the weight
of a stick of butter.
Visit an online dictionary of units of measurement:
The students are working on an experiment to simulate the impact
of an asteroid on the Earth. The experiments they are performing
are simplified versions of experiments that scientists performed
to explore impact craters. You can find out more about the Event-
Based Science Asteroid! unit at: http://www.mcps.k12.md.us/departments/eventscience/ebs.Asteroid.html
Did an asteroid impact kill the dinosaurs?
But, what about a real asteroid? You can find out more about how
we are keeping track of possible earth-crossing objects at: http://neat.jpl.nasa.gov/
The students found that mass and speed affect the size of the craters
they produced in the classroom. They tried to answer all sorts of
questions including what would happen if their asteroid hit water.
This was a difficult experiment to perform. You can see the effect
of dropping objects on a fluid at:
Want to experiment and see what might happen if an asteroid or
comet hit a planet? http://janus.astro.umd.edu/astro/impact.html
"All Objects Fall at the Same Rate"
There is a fable that Galileo discovered this "rule" by dropping
different mass objects from the leaning Tower of Pisa. This was
controversial and quite contrary to ideas of Aristotle. Galileo
knew that a feather and an anvil would not fall together and explains
his reasoning in his book "Dialogue Concerning Two New Sciences."
He knew that for extremely light objects, such as feathers, the
air resistance is an important factor, but it makes only a tiny
difference for dense, compact objects. Galileo goes on to give a
detailed analysis of falling bodies. You can read his argument at:
It was not until Newton performed the experiment of dropping a
coin and a feather down a tube in which all the air was removed
that his reasoning was confirmed. Apollo 15 commander David R. Scott
reconfirmed Galileo's hypothesis when he dropped a hammer and a
falcon feather toward the surface of the airless Moon. They reached
the surface of the Moon at the same time. http://www.hq.nasa.gov/office/pao/History/SP-4214/cover.html