Teacher resources and professional development across the curriculum

Teacher professional development and classroom resources across the curriculum

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Science in Focus: Force and Motion
About the Workshops
1. Making an Impact
2. Drag Races
3. When Rubber Meets the Road
5. Keep on Rolling
6. Force Against Force
7. The Lure of Magnetism
Supplemental Resource List

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 balsa wood.

"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.ebsinstitute.com/ebs.Asteroid.html

What Killed 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/

"Crater Size"

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: http://www.phys.virginia.edu/classes/109N/tns.htm

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


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