What forces are needed to make an object move in a circular motion at a constant speed? Can a student get around a frictionless racetrack on their first try using the race track interactive? Chances are that they can't!
-Use an object moving in a circular motion at a constant speed to introduce the idea. Flying pigs are sweet, but an object on a string could also work. Progression of ideas:
- Is speed and/or velocity constant? Is there acceleration?
- Are the forces balanced?
- Develop schema and then force diagram
- Which way is the unbalanced or net force?
- What are other examples of this type of circular motion? Gravitron ride, merry-go-round, race cars, etc.
- Try to make a rolling bowling ball move in a circle with a meter stick or mallet.
- Draw motion map -> leads to seeing velocity lines as tangent to the circle of motion.
- Then have some fun throwing a revolving ball on a string at a target! How does the ball move once it is released? What forces are on it once it is released? At that point it is a projectile and only gravity is affecting it.
-Relate acceleration to what you feel:
- Speeding up in a car -> forward acceleration feels backward
- Slowing down in a car -> backward acceleration feels forward
- Turning in a car -> inward acceleration feels outward
- Summary: you always feel the opposite of the acceleration
-Deploying the model: Unit 8 Worksheet 1 - Circular Motion and Forces. Can students relate how they feel at different places on the hill to how they feel on the elevator?
-Other examples
- Swinging a cup of water on a board
- Satellites
- Try the race track interactive again and see if students are better at it now. Check out the direction of the forces of cars that make it around the track!
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