Letting them struggle.

Today in class we were looking at four specific questions that are essential in understanding motion and Newton's 3 laws of motion. Those questions are :

1. What is Mass?
2. What makes things Move?
3. What is a force?
4. What makes something change its motion?

We started looking at a video of a plane dropping a flare and seeing it as parabolic motion. One of the students stated that the flare had a horizontal velocity and a vertical velocity. So we looked at the horizontal velocity and I asked why it had that particular velocity and it was pretty unanimous that it was the velocity of the plane before the flare was released. So I then asked what made it continue with that velocity and I got several different responses, most common was the plane's force on the flare was still acting. Someone also stated that the flare was slowing down. So we went back to the video and it showed no evidence of slowing down horizontally during its descent.

We then moved on to a hover puck on the table in front of the classroom. Again they were insisting that the force of my hand was causing the puck to move across the floor. So I called someone up from the class and asked them to apply a force to the puck. She pushed it, and then I asked her to do it again but without touching it. She acquiesced that she could not apply a force without touching it, and I thanked her for thinking so highly of me that I could apply a force without contact. We then opened up the discussion to what was required for a force to occur. We came up with four requirements for forces.

1. A push or a pull
2. Contact is necessary
1. Exceptions: Gravitational, Magnetic, and Electrical forces.
3. An agent to apply the force
4. An object to feel the force

If a "force" doesn't fit all of these requirements, it cannot be a force. So we revisited the hover puck to look at what was applied to the puck and if there were any forces involved in keeping the puck moving, discussing all of the scenarios that they brought up.

So I finally asked a different question. "Are there any forces being applied to the puck as it is freely moving across the table?" The answer to that was generally a "no" and so I then reasked question 2 from the beginning of class and someone stated "Nothing!" I asked others to clarify that and I didn't understand how "nothing" could be a real answer. I got several clarifications to my satisfaction, and we concluded to the following statement: "Why couldn't you just tell us that?" I replied that I had in the previous class and they didn't believe me or didn't remember and asked if they would forget now. I got a resounding "NO!!" and this time I believe them. There is no explanation for an object's motion. We only need to explain things when motion changes.

They struggled and they understood. They listened and they forgot.