Inquiry Lesson : Law of Conservation of Momentum

This week I have been provided with a question to explore through a guided inquiry investigation. The question is “What is the effect of large objects colliding with smaller objects?”. To find the answer to this question, I gathered the following materials: large marble, small marble, two meter sticks, paper, and pencil. On a table, I taped the meter sticks parallel to each other about an inch apart. I placed a small marble at the center on the “track” and the large marble at on end. I rolled the large marble toward the smaller one and recorded what occurred on a data table after the collision. I repeated this ten times. Each time the large marble hit the stationary small marble, the large one caused the small one to move in its same direction but at a faster speed.

 Next, I asked a friend to help with another marble collision scenario. She stood at one end of the table and I stood at the other. We rolled the large and small marbles toward each other with about the same force. We repeated this ten times, recording the results on a data table. Each time, the smaller marble changed direction and quickly rolled back in the direction it came from after the two marbles collided. The large marble continued in the original direction, but slowed down after striking the smaller marble.

Before performing this experiment, I hypothesized that when the large, more massive marble hit the stationary small marble, they would both move in the same forward direction. I was sure that the smaller marble would roll faster than the larger one because I knew that the momentum of the more massive marble would transfer much energy to the smaller one. My hypothesis was correct for this first experiment.

For the second experiment in which the two marbles move toward each other and collide, I hypothesized that the large marble would stop in place and the small marble would roll in the direction opposite of its original motion. My hypothesis was incorrect because the large marble did slow down, but it did not stop completely. After thinking about this situation, I feel that if the smaller marble had a bit more mass or traveled at a greater velocity, the larger one may have stopped completely. The mass of the small marble was not enough to halt the motion of the large marble.

The experiments were simple and worked out well. When I do this experiment with my eighth grade class, I may modify the experiment by having the students roll the small marble at the stationary large marbleas well to see what happens. I would probably  have the materials on each table ready for the students. For this particular activity, I would give the procedure to the students. There aren't many multiple ways to make this work, so unless the students can come up with the exact experiment procedure on their own, they won't see accurate results.

To make this activity more engaging, I would make momentum relevant to their lives by using examples they can relate to before the activity, such as sports examples and the motion of amusement park rides. By the end of the activity, I want the students to understand that momentum is not lost when a collision occurs (besides some lost to friction), it is just transferred. I think this activity will be successful in the classroom.