Collisions cause momentum to move from one object to another object. In everyday life, collisions occur all over the place — pool games, traffic accidents, rubber balls bouncing, baseballs being hit by bats, and more. You can probably observe many collisions just by looking around a classroom. Understanding momentum gives engineers an insight to understand different kinds of collisions. This understanding can help make cars safer, predict the results of two objects bumping into each other, or examine the evidence of a traffic accident.
I start this lesson by explaining to students that there are different kinds of collisions. Sometimes objects bump into each other then bounce away from each other, such as when a rubber ball hits the ground. Engineers call this kind of collision an elastic collision. Other times, objects that bump in to each other stick together, such as when a ball of play dough hits the ground – splat! Engineers call these kinds of collisions inelastic collisions. Most of the time, collisions are part elastic and part inelastic. For example, when a shopping cart hits a car, it might dent the car (an inelastic collision), but it also bounces off of the car (an elastic collision). We can learn more about momentum by examining different types of collisions.
Next, I remind students that we know that objects in motion have energy. I asks students to think about what happens to that energy when two things collide? Next I tell students that today we will experiment with cars to answer questions about what happens when these collisions occur. What happens when two objects are traveling together and one of those two objects collide with another?
Next, I give groups of students all materials for the lesson: wooden blocks, and two toy cars. I direct students to use their science notebooks as well to record their observations. I first direct students to sketch their two cars after carefully observing the two different cars. Next I instruct the groups to use the materials and practice having their two toy cars collide. Students will record any observations that occur during the collisions.
You can see in this photograph below that a student has first drawn his/her two cars. This student has named one car "Cheerios" and the other car "Heaviest." This is a great student example to show that this student also knows that the red car is heavier than the other car.
You can see in this video, students exploring crashing their cars together. Notice how the cars are let go of at the top of a ramp. This was an important last minute decision I made. I didn't want students pushing one car more than the other, causing it go go faster and have more energy, so I instructed students how to make a ramp with their wooden blocks. Next, I asked students how they could make their cars go faster without pushing them. Students were able to identify that they could make the ramps steeper.
Watch in this video as students observe cars crashing.
Next, I bring the class back together, and demonstrate what students have discovered. I then allow students to use their own words to describe their findings by telling the class about their exploration. I help lead the discussion by asking questions like: Were you able to find a way to move two objects at once and have one collide? What happened?
I discuss with the students the idea of collisions and energy. I begin this discussion by showing this Mythbusters clip about collisions.
Students turn in their notes from the day with a write up of their findings. The diagrams in the notebooks and their explanation of what they learned will help to show student understanding. Teacher also has the chance to move around the room to evaluate the learning
You can see in these two student work samples below students recording what happened to the cars as they collided. Students also recorded the height of their ramps to the nearest centimeter. As students worked, it was important that I circulated around the room and assisted with measuring the ramps. Some students were confused about how to measure the height of the ramps.