Trying out a Different Trajectory

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SW examine videos of themselves to determine the motion of the block in the bucket drop and develop a theory of how they can alter their motion to be successful.

Big Idea

Students intuitively understand the idea of trajectories from sports and other play. This lesson gives them an opportunity to diagram and write about that understanding.

Re-engage and Explain

30 minutes

Students begin this lesson by looking at some footage from yesterday's lesson.  If you were unable to make a video, it is my hope that this video will suffice.

To make the video, I used a traditional camera and MovieMaker to slow the action.  There are many programs out there that do this equally well or better.  FastCamera on the iPad takes multiple photos within a second and would be another excellent way to record the demonstration.

Prior to showing them this video clip, I remind them of the constraints of yesterday's demonstration.  They were to:

  • run as fast as possible, without slowing down as they passed the bucket.
  • drop the block when they were directly over the bucket.
  • keep their body erect and resist the urge to lean into the bucket as they passed.

As they watch the video, I ask them to pay very careful attention to the trajectory of the block. They are to draw a few diagrams showing the direction in which the block continues to move after it is dropped.

 This can be done on blank paper or in their science journal.  I created this 

Thinking About Trajectory page to facilitate students' focus on the diagram itself.  Third graders can be perfectionists about their drawings and I didn't want them to get derailed trying to draw the perfect bucket.  

(Here is the same file as as a Word doc that can be modified: Thinking About Trajectory.docx)



25 minutes

By now some of the students will be making the connection from what they read and observed from the first lesson and what happened in the demonstration.  They will realize that the block doesn't drop straight down because it is continuing, briefly, at the same speed and same direction as the runner.  Gravity is also acting on the block and it is an unbalanced force, as there isn't an equal and opposite force on the top side of the block, so then it also falls down to the ground.  

Yesterday at the end of the lesson they were asked to write down a hypothesis about how they could possibly get the block in the bucket without, still without slowing down or bending.  I don't explicitly state it, but they no longer are required to drop the block immediately above the bucket.  Intuitively, most of them release before they reach the bucket.

Students shared their hypothesis with one another and then we went outside to the basketball court to try it out.  Tomorrow they will write about what happened differently today.  I took video again and at night went home and clipped it and slowed it down so they could view and analyze it in the next lesson.


5 minutes

When we return to the classroom, I ask a few students to share out their observations about how today's activity was different from yesterdays.  While we were outside, they were engaged the entire time with their peers about the success and failure of their various hypothesis, so there was already an organic pair-share.

I ask them to share their observations with someone at home and tell them that tomorrow we will watch the videos from today and diagram what occurred.