Demonstration #1

The first demonstration asks students to think about motion over time. Students are asked to think about what happens as a body in motion moves in an ideal situation (ie. zero losses due to friction, heat, deformation of material, etc...) and then predict what they think will happen in the low-friction case of the air hockey table. What factors do physics thinkers need to take into account when applying textbook formulae to situations that arise in the world?

 The first demonstration simply sees the puck move along the table and collide with a wall and move back, ideally to the initial position.

On the worksheet students are asked to draw the position-time diagram for the ideal case and predict the velocity (ie. slope of the curve) before and after the collision, given an initial velocity. After the demonstration the position-time graph for the motion will be given based on the data collected from the video and students can compare and contrast what is predicted in the perfecct case, and in the case with little, but some, losses.

Some action shots of the demonstration:

 

 

 

Screenshots from the analysis in logger pro of Demonstration #1:

 

Demonstration #2

The second demonstration introduces students to collisions. Students are tasked with understanding basic momentum formulae and describing which situations they apply to. Students are encouraged to consider which factors the individual formulae take into account and which they might not. Students should see that the formulae are accurate in describing the general motion of the pucks but simplify the mathematics by making assumptions. In the demonstration we see that these assumptions may lead to small differences between what we predict and what we see. Students will be encouraged to understand that all of these changes are described by more complete formulae that they may encounter later in their physics education.

 To do this two pucks are shot with opposite velocities and allowed to collide and bounce off each other. The velocities and momentum of the pucks are determined at various times in the motion of the pucks.

On the worksheet students are asked to consider elastic and inelastic collisions and use these terms to describe the collisions they observe in the demonstration. They will be encouraged to consider what effect the elastic or inelastic nature of the collisions will have on the results we obtain in the analysis portion of the demonstration.

Some action shots of the demonstration:

 

 

 Screenshots from the analysis in logger pro of Demonstration #2:

 

Demonstration #3

The third demonstration encourages students to think about transfer of momentum and transfer of kinetic energy. Students will continue to be encouraged to think about the sign of momentum and of the differences between a scalar property like kinetic energy and a vector quantity like momentum.

This demonstration is performed by looking at the initial velocity of a single puck in motion and observing what happens as it collides with a stationary puck. If done as shown in the video below, the velocity of the puck that was stationary before the collision, should almost equal to the velocity of the initial puck (it will likely be slightly smaller due to losses during the collisions).

When alaysing the demonstration students will likely predict that the veloity of the second puck after the collision will be equal to the velocity of the first puck before the collision. In reality it will be close but not exactly the same. This is a good opportunity for the demonstrator to dicuss potential sourcces of error or losses during the collision that cause it to be slgihtly different than predicted. Students can be encouraged to predict how formulae might be modified to accomodate these factors. This could include, for example, a Q term added in the energy equation that absorbs all losses due to frictional and other forces.

 

Some action shots of the demonstration:
 
Screenshots from the analysis in logger pro of Demonstration #3: