Lesson 9: Mass distribution; motion of a balance
Grades: all, depending on the leading questions
| Possible Questions
Do all the Rickey sculptures have a balance point?
Why do most of them move slowly?
Discuss everyday examples of things that move/rotate slowly or rapidly?
How many “balance points” are there in Rickey sculptures?
The questions are focused on the reminding or demonstrating the idea of balance (can be done with a meter ruler on a knife edge).
Try to get the class to realize the importance of how far the mass is from the balance point
- then they will test out their hypotheses in the group-work.
Hands–on: Each group can make a hypothesis about the mass distribution
- and then build a “mobile” or equivalent to test their hypothesis.
Summing up the experience: Whole class discussions
All grades should be able to compare simple mobiles (as in children’s playpens, etc) with the more complex Rickey sculptures.
The higher grades can discuss the balance and motions of models analytically:
above 6th grade for “balance”;
high school students can discuss HOW FAST the balanced objects move.
An alternative exercise for the higher grades is for some groups to build a pendulum,
and then add weights at different points on the string to see how it changes the time of the swing
- a good exercise for developing the idea of “the center of mass”.
Extensions: What are the differences between the effects of (variable) wind force and (constant) gravitational force to produce motion.
How do clocks work? How are they adjusted to keep good time?
Sc.2.3.7 Investigate and observe that the way to change how something is moving is to give it a push or a pull.
Sc.7.3.17 Investigate that an unbalanced force, acting on an object, changes its speed or path of motion or both...
M.4.4. Students show an understanding of plane and solid geometric objects and use this knowledge to show relationships and solve problems.