Lesson 5: Relative Motion

Maureen Dooley, B.S.Ed.

Copyright 2004. Permission is granted for classroom use and for non-commercial educational purposes.

Subject __________________________

Grade Level _______________________

Anticipatory Set (focus) - The students will write down what is written on the board. Einstein said that you cannot tell the difference between the "real" and the "artificial" gravity. After writing down this down the students will prepare to discuss what is real and artificial gravity.

Purpose (objective) - The students will begin thinking about the motion of the pendulum, they will discuss the idea that motion is relative and they will question and analyze what mystery force turn the pendulum.

Input - The teacher will teach/re-teach some or all of the following: Motion is relative; the motion of one object is always detected by comparing it to another object. (The "other object" might be the classroom.) Newton thought about the centrifugal force that makes water pile up on the sides of a spinning bucket. The piled-up water is evidence that the bucket is "really" spinning. You can tell that the bucket is in motion with respect to the fixed stars.
But the motion is still relative: Einstein said with general relativity that if the stars revolved around us, the water would pile up in the same way. With this in mind, how can you tell which is "really moving" in a circle, you or the pendulum? What if you stood on a rotating platform in a dark room and a pendulum stood on another. Both platforms have the same center. You cannot tell who is "really moving".

Modeling (show) - The pendulum should have remained in motion since the previous lesson. It is likely that it is now swinging in a direction different, as revealed by the log. Another log entry should be made at the beginning of the class. If it is not possible to leave the pendulum running, it should be started as soon as possible, in the same direction as it was started in the previous class.

Guided Practice -The teacher will divide the class into pairs and then the teacher will ask the students to come up to the pendulum and look at what is happening. The students will be told to observe and record any changes in the motion of the pendulum they observe. They are to be told to then discuss with their partners what they observed, what changes they observed and then hypothesize as to why the changes they observed took place. (If a direction change is observed, the first guess is that someone bumped it.)

Independent Practice - The student pairs will look at the pendulum and record what they see, and they will discuss with their partners why they think the change in motion occurred. This will not necessarily lead to a reason for the change, but just that a definite change did occur. The pendulum's motion changed from the plane motion that it was put in by the teacher to the motion it has maintained since being introduced to the class several days/lessons ago. What is left to be discussed is: What is the mystery force that caused the change in motion?

Closure - (Tell or show me what you have learned) - The teacher will ask the students to share with the class their observations, the changes they observed and their hypothesis as to why the change in motion took place. The teacher will ask if anyone knows what the mystery force is? This does not need to lead to a correct answer, just to lead to more questions and thought.