Spring demo set-up

I joke with my classes that the last class of the day gets the best version of me. At least today it only took one period for me to get this worked out.

My AP Physics C are studying simple harmonic motion and the most common type is a block attached to a spring on a horizontal friction less surface. Surprisingly our book does not touch upon springs in series and parallel. Students did a quick activity using PhET's Hooke's Law simulation the other day, leading them to the equations to find the equivalent spring constant if series and parallel pendulums. We ran out of time that day to show it to them live so I set it up for the next day.

I had two identical springs of spring constant 20 N/m +10% that I hung from a horizontal support attached to two large ring stands. I used a pegboard hook to link the two springs when working in parallel which made it easier to hang one mass from it. For the first class of the day I hung a 500 gram mass from a single spring, then the two springs in series and then in parallel so the class could see the difference. The series elongation was very easy to see the difference but the parallel elongation was harder for those in the back. So I added to it between classes.

I used bright post-its and labeled the natural length of one spring, where it stretched to in parallel and in series. I taped a measuring tape in line with the top of the spring so if I wanted to, I could do calculations. It made for a much better visual for the students.

After the fact I realized I wanted to add a marker for the natural length for the two in series since the new length is much larger than twice the stretch of the single spring because of the additional length of the second spring. If I had enough springs of the same spring constant I would want to have all three setups up at the same time. Add that one to the wishlist I guess.