Day 25: Dueling Fan Carts


Based on the bowling ball and mallet activity, our force-motion model was:

  • tapping = changing motion 
  • no tapping = constant motion 

Enter the dueling fan carts. We go through various configurations of fan speeds:

  • high vs. off 
  • low vs. off 
  • high vs. high 
  • low vs. low 
  • high vs. low 
  • high vs. high THEN push them…what happens next? (LOVE this.) 

And if you’ve got the fancy Super Fan Carts pictured above:

  • Put one fan on HIGH, then set the second fan to turn on HIGH after a delay…what happens? (CA then CV)
  • Put one fan on HIGH, then set the second fan to PULSE on HIGH after a delay…what happens? (CA, CV, CA, faster CV, CA, even faster CV, etc.)

Based on the demos, we refined our model to:

  • net tapping = changing motion 
  • no net tapping = constant motion 

NOTE: Before showing the fan carts, I did a series of anchor and bridging demos to show the fan cart moves because it is being “tapped” by air molecules:

  1. Used leafblower to accelerate a hover puck. Air molecules from blower “tap” the puck to change its motion. 
  2. Tossed a bowling ball to a kid sitting in a rolling chair. Bowling ball “tapped” kid to change its motion. 
  3. Kid in rolling chair tossed bowling ball back to me. Kid “tapped” ball to change its motion. And, since kid’s motion changed, ball “tapped” kid also. 
  4. Fan cart: Blades “tap” air, air “taps” blades too. 
  5. Also did a series of dynamics cart collisions to show both carts change their motion due to the interaction, therefore they “tap” each other. 
  6. Also came back to the mallet and bowling ball — mallet usually bounces back slighty when striking the ball, therefore when the mallet taps the ball, the ball taps the mallet back. 

We’ll deal with the magnitudes of these mutual taps another day.

The dueling fan carts are revisited during the Unbalanced Force Particle Model Unit to develop a=F/m qualitatively and to illustrate why objects of different masses free-fall at equal rates.

About Frank Noschese

HS Physics Teacher constantly questioning my teaching.

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