Predict shape changes in collisions

2.A Collect data on changes in the motion and shape of colliding objects within a system that serve as the basis for evidence that energy transfer occurs during the collision and that there are forces between colliding objects.

Listen for students to suggest ways to control the collisions they observe. For example, they are likely to suggest that they want to see how the materials themselves are changing during the time the objects are in contact with each other. They may also suggest ways to control the motion and speed of objects in collisions, such as a way to target or line up the objects to ensure that they will collide after one or both are put into motion. Students may also suggest the use of slow-motion video or zoomed-in images of the moment of collision.

To elicit ideas for making better observations during collisions, ask students to think about what should be different about their experimental design. If students still don’t have a lot of ideas, add an optional exit ticket at the end of day 1 that asks students to reflect on what about the new setup in the Exploring Horizontal Collisions Lab helped address some of the challenges they raised at the end of the Dropping and Breaking Lab and/or what about the new setup allowed them to make the kinds of observations they were not able to make as easily before.

Say, I think we can do some things to control for many of these variables in our next round of collision investigations. I have some equipment we can use that I think might help address some of the challenges you raised. Let’s consider how the available equipment could be used to help address those challenges.

Project slide D. Say, In this image putty was used to attach a golf ball to a cart and it was also used to attach a CD case to a second cart. Notice that both carts are also on a track. This is just one sample of two different kinds of things we could collide together. We could swap in other objects and still attach them to carts using putty. Discuss the question on the slide as a class.

Suggested prompt

Sample student response

How would investigating collisions using this sort of setup help us address some of the challenges we encountered in the previous investigation?

• This would allow us to control where the ball hits the target.
• It could help keep the ball from flying off after the collision.
• It will keep everything in a more controlled space.

Define the system of objects that will be involved in the collision. Say, It seems like we have ideas about better ways to collect observations during a collision, but since there are different objects in the new system that we are going to use to carry out a collision, let’s think about one example of two objects we can collide together within this system. We could collide a golf ball with a CD case if we attached each to their own cart and ran one into the other. In this example, where would we expect the point of contact in the collision to occur?

Students will say the point of contact will occur where the golf ball and CD case touch each other.

Say, OK, so even though the golf ball is attached to one cart and is part of that subsystem and the CD case is attached to another cart and is part of that subsystem, the point of interaction we are really interested in studying within the entire system is just between the two objects we identified at first: the golf ball and CD case. Defining what parts, objects, or subsystems within a larger system we are wanting to study the interactions between is an important part of systems thinking that we should keep thinking about going forward in all our investigations and models we develop.✱

Turn and talk. Project slide E. Ask, When the objects that are part of the two subsystems make contact during a collision, what sort of changes do you think you might observe in those objects or in the subsystems they are attached to? Ask students to share a few responses and listen for ideas about whether the motion, the shape, or both motion and shape will change during a collision. For example, students might say that the cart subsystems will bounce backwards or stop, the CD case will wiggle or crack, or the putty will be squished more or less.

Demonstrate controlling collisions with carts. Distribute Exploring Horizontal Collisions. Project slide F. Have students write the investigation question, What happens to the motion and shape of the objects (and the subsystems they are part of) when they collide?, on the top of their handout as described on the slide.

Prepare for data collection. Say, The data table provided has space for you to keep track of what is happening to two separate things for two different objects in the system, which is a lot for one person to pay attention to. Tur…