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## #1300. Thinking About Newton's 1st. Law

Science, level: Middle
Posted Wed Sep 15 10:48:13 PDT 1999 by Ben Rogers (ben@ben-rog.freeserve.co.uk).
edmonton county school, enfield, london
Materials Required: two short texts (can be on board)
Activity Time: 30 min.
Concepts Taught: analysing scientific writing about motion

Considering Newton's First Law

For many pupils Newton's first law is difficult to understand or believe. It has been observed that many kids are "Aristotelian" in their beliefs. Hmmm.
This lesson is designed to:
 Increase the student's historical perspective of an idea's development.
 Develop the pupil's ability to interpret texts.
 Develop the student's understanding of Newton's first law.

1. Discuss a little about Aristotle and Newton. Emphasize the originality and importance of them both. Explain that they each developed ideas about motion, but one of them was wrong. (I like to stress how smart they both were).

Aristotle (384-322 BC): Aristotle was Plato's student. The philosophy of the time was to discuss ideas until everyone agreed. No one thought of checking by experiment. Aristotle had a range of strange ideas. He believed that all matter was made from earth, air, fire and water, and that any material moves towards the layer it belongs to (fire being the top level, then air, water and rock as the bottom layer). He also believed that heavy objects fall faster than light ones. Aristotle's ideas of motion were not proved wrong for about 2000 years. This is not a bad achievement!

Newton (1642-1727): Very bright boy, but very odd. He forgot he had guests and went off to do some work. Part of his work was an attempt to turn lead into gold. It took him just 18 months to write physic's most important book, "Principia Mathematica" while the plague was sweeping through Britain. His laws of motion were considered the whole truth until Einstein discovered relativity. Even now Newton's laws of motion are used to calculate the flight paths of space probes. This is not bad.

2. The following two texts are shown, without revealing the identity of either author.

 A body in motion can maintain this motion only if it remains in contact with a mover.

 Every body continues in a state of rest or uniform motion in a straight line unless acted upon by an external impressed force.

3. Get the students to rewrite each statement in their own words. It is probably better to do this in groups.
4. List evidence supporting and contradicting each statement.
5. Then get each group to decide which statement is correct. They could consider such things as comets and asteroids, very well oiled bicycles or very rusty ones. Their job is to explain to the other groups which statement belongs to Aristotle and which one to Newton.

A useful tool for this discussion is the air track (or similar device). The important idea is that an object will not stop if there is no friction. I use the air track and ask them if the carriage is slowing down. It does. I then ask what slows the carriage down. I suggest that this force could be reduced. Would the carriage continue moving for longer? What about removing this "slowing down" force altogether?

Last point: Decide whether the following statement agrees with Newton or Aristotle:

"The stopping of motion is due to the opposing force. If there is no opposing force the motion will never stop. This is as true as that an ox is not a horse. (China 200/300 BC)"