Intro to Forces activities

 A few years ago I changed the order of activities and my introduction notes for Newton's Laws in my college prep physics class and it has been a lot of fun. We do a few days of activities and labs before I even start notes, this is day 1. I start off by asking students to take some blue painter's tape and make part of a track on the floor that goes all the way around the room. They get this image for inspiration and they end up adding a lot of difficult turns, loops, etc. I don't tell students why yet, but if they ask I just tell them we will need it later. 

Then each group gets a lab basket that has two tennis balls in it. I ask them to make observations. The first observation is usually that when they pick them up, they are surprised to find one tennis ball is quite heavy compared to the other. I give students this prompt:

You have two tennis balls, not to be thrown. Holding them in your hands, what do you notice that is different about them? Hold them a few inches above the table and let them drop, do they act the same while falling? What about when they strike the table? Put both of them on the table and try to push them with your hand gently, what happens?

Sometimes there is fierce debate but they all generally come to the same conclusions. Then I give students a paper that has these prompts on it: 

While holding the tennis balls in my hand and moving them….
While falling, the tennis balls….
When I push the tennis balls across the table …
When the tennis balls hit the table after falling ….

Students take a few minutes to write out their responses then I call on different students to share what they/their group wrote. Usually by now they notice that the paper I gave them also mentions the bowling ball... 

"Wait we are going to hit a bowling ball with a mallet??"

Their instructions say: 

Use the rubber mallet to try and move your bowling ball around the path on the ground. Pay attention to the direction you have to push the ball with the rubber mallet and how much. What part of the path was easier to maneuver? Which part was harder?

They may have noticed earlier that there are bowling balls in all of our sinks. Then I bring out a pile of rubber mallets. Each member of their group will take a turn tapping the bowling ball with the rubber mallet around the track. This is when they start to regret their choices. Now the crazy curves and zig zags seem like a bad idea. This year's track even had a "6 7" portion to it. 

Students find that the bowling ball is hard to get going with just "taps." They will wind up as if to impart a large force only for it to lazily roll forward. When the bowling ball gets going too fast, they find it hard to stop but intuitively know they have to tap in the opposite direction than it was moving. The loops are fascinating, students quickly find they have to tap towards the center of the circle for the ball to navigate the loop, which I remind them of when we get to circular motion. There are some sections they just roll past, ignoring the complicated zig zags for example because they know it will be hard to change the bowling balls' direction. 

After each student has a chance to tap the bowling ball around at least part of the track, they sit down to do the next part of the worksheet. And they groan.

Draw the path you attempted to follow with the bowling ball as a solid line. Draw an estimate of the path you actually moved the bowling ball through as a dashed or dotted line.

Add observations to your drawing about where it was easier or harder to move the bowling ball.

They ask if they have to draw it exactly as it is, I tell them to do their best. Since they weren't writing down exactly where they went outside of the track, they have to estimate it when they draw it, and they do that part well. They remember that they, generally, couldn't take the turns as tightly so their "actual" path of the ball is larger than the path they tried to follow. 

Students continue to reinforce the concepts by answering this last question: 

In order to make this left hand turn, which way would you have had to push the bowling ball with the rubber mallet? Explain your answer.

All in all, the activity lays a lot of ground work for later and I find it to be a fun introduction. The students enjoy it, even if I make them clean up all the tape before they leave.