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Content Standard III (State PASS Standard 1):
Forces and Motion
Topic:
- Laws of motion (state standard 1.1)
Objects change their motion only when a net force is applied. Newton’s laws of motion are used to calculate precisely the effects of forces on the motion of objects.
Time Range:
6 weeks
Suggested Teaching Strategies:
- Use inertial balance to introduce mass concept; use airtracks or dynamics carts to illustrate force, mass, and acceleration relationships; use various tricks to demonstrate law of inertia (see core labs).
- Carefully define action and reaction as forces between two objects; demonstrate using two force probes pulling on each other, with inverted graphs of F vs. t showing on computer monitor. Have students create free-body diagrams for a donkey pulling a cart (7 significant action/reaction pairs) or a student sitting in a chair (illustrates confusion between weight, normal force, and identification of the true reaction to weight: earth pulled up by object). Discuss complexities and misconceptions in applying the third law to rocket propulsion (no need for atmosphere; action and reaction can be vaguely defined as rocket pushing gas and vice versa or more precisely defined as exploding gas particles pushing on combustion chamber walls, etc.).
- Check student understanding of laws of motion concepts by having them identify and correct the errors in various statements that contain a misconception or misstatement of one or more of the laws as applied to a situation (e.g. "A ton of feathers on earth has the same inertia as a ton of feathers on the moon.")
Aligned Resources:
Revision Date:
June 2004
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