One of my favorite days of the year: Broom Ball Relay! This is our introduction to the Forces Unit, used by lots of modelers. The activity is really fun and is one of the most central lessons that we draw back on throughout the course of the year (and in AP Physics too). We set up a relay course on a flat, smooth indoor surface (the gym works great when it is available). The Essential Question we used was “How are forces, motion, and inertia” related? Students participated in a relay course by pushing a bowling ball from one end to another. This included making a hard turn, making the bowling ball travel through the ‘no touch zone,’ and getting the ball to come to a complete stop at the start/stop box. Quite a few students either made the same mistakes as those who went before them (“it’s harder than it looks”), but some also learned how to perform parts of the course well and coached their teammates through the course.
The best parts of this are how evident it is that it is hard to turn the ball once it is moving fast, the fact that the ball moves with a constant velocity in the ‘no touch zone’ and also how difficult it is to stop the ball in the start/stop box (the ball isn’t stopped until a Physics teacher says that it is stopped). For years, I have watched students push the ball in a way that makes it move in circles, over and over, just inside the edges of the start/stop box. Instead of getting the broom out in front of the ball and pushing against it’s motion to stop it, it is common to keep pushing on the side of the ball, making it turn. Often, the student looks up with a worried look when it becomes evident that this isn’t working. I have come to realize that (I think) that these students are attempting to stop the ball by pushing it into the center, not knowing that this is exactly how circular motion is made. This becomes an important discussion point and becomes a key idea in our Central Force Unit later in the year.
After the activity, we debrief by connecting this activity to the ideas of force, net force (or ‘sum of the forces’), and inertia.