Category: Activities

Impulse-Momentum Activities
Activities · Teaching Methods

Impulse-Momentum Activities

Marianna Ruggerio1 Comment

This is post 2 of 3 on how I (currently) teach momentum in my physics classes.See how I introduce the momentum unit here

you might also like my physics classroom companion worksheets!

In this post I will outline 3 activities I do in my classes. Each serves a different purpose and function depending on the group of students, but most could be used interchangeably between levels depending on your own goals. They are the following:

  • Pivot Interactives: Ball on a Wall
  • Popper Lab
  • Egg Drop Challenge (with a data-driven testing phase)

These activities are all about giving students a “real-world” opportunity to collect data and calculate quantities from the course. There’s not a lot of “discovery” going on here, a primary driver is practice. However, each activity presents rich opportunities for different conversations.

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Pivot Interactives Activity: Ball Against a Wall (regular level)

Many of us came on to Pivot Interactives after the original library was migrated from “Direct Measurement Videos” many more of us came on to PI when we had to teach in the pandemic. If you can push for a subscription it’s very much worth it. Labs that are too expensive or cumbersome for a class set become attainable, make-up work, homebound, remote learning… you name it. There are a lot of benefits. I love this very simple activity that just involves a ball colliding with a vertical wall. Important note: I don’t use the built-in questions/grading set up in pivot. It’s very well done, but I find that computer work usually hinders collaboration, so I moved away from having students answer in pivot even before the pandemic.

Ball against a wall in Pivot Interactives

Students begin this activity by reviewing the transformation of F=ma to the impulse-change in momentum relationship. The mass of the ball is provided and students have access to a ruler tool and stopwatch. There are a lot of ways this could be done. For my regular students I have them determine the pre and post collision velocity as a simple x/t calculation (we verify it’s moving constantly by seeing it move equal intervals down the ruler in equal frames). The biggest challenge is determining the time of the collision. This is one thing I love about this activity. In day to day life collisions happen so fast we don’t really consider the impact lasted for a measurable time. I love how this visualizes. You can see my original handout here. Last year I discovered that remote students do better when labs were broken into very small tasks through jamboards, so also check out the jamboard activity here. (2026 Update: Take a look at some of my new summaries for pivot activities!) You will notice a lot of scaffolding. This is necessary for my regular level students, but it may not be for yours. When I run this activity in AP I simply inform them of the goal and send them on their way.

Popper Lab (APP1)

I took this lab from an AP summer institute I attended under the direction of Martha Lietz. Students pop a popper toy (the half-spheres you turn inside out). The ultimate goal is to calculate the time for the “pop”. While students end up using impulse-change in momentum, they also have to use kinematics and F=ma along the way. I find that many students have a hard time with this interleaving because up until this point (remember I do momentum right after forces) we haven’t had too much of a chance to interleave yet. That is one of the main reasons this lab has been a mainstay for me, even if it’s really just a “glorified homework problem” as I tell my students. Students are taken step by step through the process. See the activity here. At the end of the lab I ask students to submit their calculated times to a google form where I aggregate all of the responses. We will first do a quick skim on day 2 so if students calculated an egregious answer, they can obviously see they need to check something. Once we remove the outliers, we do an average and standard deviation. It’s SO COOL to see how close student answers all are when it feels like such an imprecise activity! Because this is a glorified homework problem we can take some time to have a solid conversation about measurement, uncertainty and standard deviations, making it appropriate for AP.

Egg Drop Lab

Whenever students hear we are going to do the egg drop they respond gleefully “we did this in middle school!” I am quick to explain why this is not like middle school and the middle school experience was not like science. In middle school students are typically given tons of supplies, they can use as much as they want and they just cobble whatever together and start chucking. Can you imagine if engineers did this? What a waste of dollars and materials! Besides, you shouldn’t even think about messing with materials unless you have some kind of idea about what is going to happen.

I explain the parameters: 5 sheets of 8.5×11 paper and 1 meter of masking tape. The device must be attached to the egg. No parachutes.

The reason for these parameters is I want students to be thoughtful about the why behind their device.

But no devices are built without prototypes!

So on day one we have a testing phase. (See handout here) Students use force probes and cars or iOLabs and run “prototypes” into the probe (see image below for how I set up the probe). This might be folder paper, crumpled paper, tubes… whatever! But we know that our eggs will be saved by one thing: increasing the time of impact and decreasing the force.

This activity is by no means precise, but it gets students thinking about what to actually do with the paper.

On drop day students have roughly 35 minutes to build their devices which we drop in the last 15. Students present their devices to their classmates and then drop from 2.0 m. Eye of the Tiger plays on loop in the background.

The following day I ask students to whiteboard diagrams of their devices that also show where the egg was located. We discuss the designs in relation to their smashing or success. View the activity here.

None of these activities are ones I would consider particularly awesome and certainly not flashy, however often its these kinds of activities that allow the nuances to shine.

Souped Up Soup Can Demo
Activities

Souped Up Soup Can Demo

Marianna RuggerioLeave a comment

At an AP Institute I was introduced to the demonstration where you roll different cans down a ramp and a can of broth is ridiculously fast compared to others. The reason, of course, is that the low viscosity of the broth means the liquid does not spin. In turn the fast majority of the can + contents has translational energy only.

I wanted to do something more with this excersice than “guess which is which”. After some poking around I settled in on this lab that I now run each year. Be forewarned: the results aren’t spectacular, but the lab comes back with great data and a great experience. Students regularly report this is their favorite activity of the year.

We start by laying the foundation of the race. I have 5 cans: An empty can with the lids off, an empty can with lids, refried beans, condensed cream of mushroom soup and chicken broth. I provide students with the following information and ask students to rank by which gets down the fastest.

We share results and comment on similarities. Groups generally predict the empty can without lids will be last, but the rest gets messy. Did students put the refried beans because it was a cylinder or because it has the greatest mass? Where do you put the broth (many throw it in the middle). The cream of mushroom soup has a smaller diameter.. how does that matter? We’ve talked about all of this already, this is a great application.

After our discussion (mass is irrelevant, radius is irrelevant) we talk about modeling each can. The empty cans and the refried beans are obvious: hoops and cylinders. But what about the mushroom soup? When you dump it out you get a cylinder of soup in the pot, so it’s like a hoop + 2 disks + a cylinder of soup. We race the “obvious” ones…empty vs beans, empty + lids vs mushroom soup. Then we race the winners and losers… empty first. I poll the class about the beans and soup. It’s a 50-50 split. I tell them this is a good guess. We have tot race best 2 out of 3. Beans wins by a hair.

Then enter the broth.

After broth is the hands down winner, we talk about what’s happening. What is the liquid DOING? (Many studnets think itt’s spinning like a hoop). I demonstrate with a VOSS bottle and dyed water (VOSS is nice and smooth).

For homework I ask students to develop an expression for ANY object down the ramp. How can we do this? Well one thing worth noting is that every moment of inertia is some object MR². So let’s replace “some number” with k. I tell students they need to figure out the expression and what they will plot to yield a straight line and what the slope will represent.

The next day we review student work. It’s a cool derivation.

We get down to the fact that students need a graph of v² and height. Ok cool. But how will we compare our results? We go back to the models. Students are responsible for coming up with the velocity at the bottom of the ramp for their assigned can. For this activity I put students in ability-level groups, assigning the empty cans and the beans to the students who are usually C and lower, the broth to my B students and the mushroom soup to my A students. (more on that choice another day). After students have a chance to work through their derivation we review all of them. One of the things we discuss previously is that when determining velocity at the bottom it’s always the √number*g*h and that number is between 1 (hoop) and 2 (sliding only). The numbers we get all fall in line with our expectations and observations…including why mushroom soup and refried beans are such a close call!

Student work for can of chicken broth.

Before we begin the lab we need to have a discussion about reducing error. We have a major problem. Height is easy enough to measure with little uncertainty, but we are looking at an expression with final velocity SQUARED. This is problematic for several reasons. First, the square means that uncertainty is going to propagate and blow up. Second, we’re looking for FINAL velocity. Cherry-picking that data point is sure to be messy with tons of uncertainty and, frankly, a waste of our tools. So what IS consistent and reliable no matter what we do? Students quickly realize it’s acceleration! We know how to best collect that data from other labs: run a regression through the position or velocity graph. We can then use a spreadsheet to manually calculate the expected final velocity for a specified distance.

Students are able to get data that generates amazing straight lines and then they use that data to determine the moment of inertial of their cans.

Student data for chicken broth

Some of the cans will be pretty far off from the theoretical models, but that’s ok! We tried to really simplify something real and complex! (The original idea from which I got this the activity used cans filled with concrete and other materials that are much closer to the models.)

For the full activity and handouts, I’m sharing here!

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