Great Lesson Ideas: Why Do I Need to Wear a Bicycle Helmet?
with Mike Rettberg
Mike: My name is Mike Rettberg. I teach 8th grade science. And, this unit will help you answer the question "Why do I need to wear a helmet when I ride my bike?"
"All right. Here we go!"
"All right. Ready? 1...2...3..."
We're exploring the ideas of force and motion. So the purpose of the demonstration is to create a key experience. Something that we can talk about, um, in subsequent lessons, and just keep referring to. So right now, we're about half way through the unit, exploring the model of an egg for your head, and talking about collisions to apply Newton's laws, which we've been learning about, to this demonstration.
So this is a unit that takes about six weeks, start to finish. The demonstration is repeated four times throughout the unit. The first time is just as an introduction. So, let's watch the egg collide with the barrier, and then write. So, initially their explanations are very simple, kind of what you'd expect from anybody.
Then as we learn concepts, like acceleration, inertia, force, motion, Newton's first, second, and third laws, they'll have to re-write an explanation.
"So what we're going to do is, we're gonna look back at the work that you did a couple of weeks ago, when we were just starting the unit, thinking about "Why do I need to wear a helmet when I ride my bike?" What I want you to do is re-read what you wrote last time, and then you're gonna re-write. You're gonna make a new prediction. What are we gonna see today? When you are writing today, I want you to think about our Word Wall. I want you to think about our vocabulary words. Could you use the word acceleration? Could you use balanced force? Can you talk about momentum?"
And, so we have, you know, have the students predict, and then write.
"All right. Please turn and share what you've written with somebody in your group."
Then you also saw every time after they write, they had to turn and talk, and share what they wrote with their neighbor, so they're just practicing using the words and getting comfortable.
Student: "The acceleration of the egg was faster because it had more mass."
Mike: If you want kids to acquire new vocabulary, you have to teach it in a variety of ways. Like, if we don't discuss the words, if we don't practice using them, they, they remain, you know, words that are up on the wall that a student might think "OK. I'm gonna use this in science class."
Student: "Force equals mass times acceleration."
Mike: "OK. Can somebody explain that for me in their own words. What does that mean? What was Isaac Newton telling us?"
The valuable part, the learning part of it, is when we then discuss and talk about it.
Student: "The momentum of the cart..."
Student: "will accelerate as it went down."
Student: "Gravity will work as an outside force."
Student: "Newton's third law of motion explains"
Student: "when the egg and the cart hit the barrier"
Student: "the inertia of the barrier will cause the cart to bounce back, and"
Mike: Vocabulary kind of floats on a sea of talk. And, so what I'm really trying to do is just get them to use the words as much as possible.
"Let's take a look at question number 1. So, what we're going to do is..."
So today's lesson, the first question that the students investigate is the idea of "What happens as the egg and cart travel down the ramp?"
Student: "The cart will increase acceleration as it travels down the ramp."
Mike: It's really based on Newton's first law of motion, the idea that objects in motion stay in motion. We talk about acceleration, things like that.
"Both the cart and the egg will what?"
Student: "Build up momentum"
Mike: "OK. I think that's a pretty good prediction. I would like to hear two of our main vocabulary words incorporated here that I'm not hearing so far. What are the two main vocabulary words?"
All: "Force. Motion."
Mike: "Do those belong in here somewhere?"
Mike: "All right. So, somebody tell me where we can incorporate those words into our prediction."
Student: "The pull of the gravity."
Mike: "Yep. So, we could add 'gravity is pulling on both the egg and cart.' "
I'm trying to get the rest of the class to comment on what's good in here. Who can tell what's missing in here? Who wants to change something in here? And, so we actually end up going through, like, just changing some words, maybe adding something new, so that we develop as a class. OK, here's what a good prediction, um, would look like.
"Yameleth, read me question number two please."
The second question shifts and asks them what happens just at the moment of that collision between the cart and the barrier. This is more of a demontration really of Newton's third law of motion that
Student: "Every, every action has a reaction."
Mike: "And what about that reaction needs to be.."
Mike: "Equal and opposite reaction. So we're expecting that the cart is going to... Richard."
Richard: "The cart will bounce back, then go back, hit the barrier again, and stop."'
Mike: "OK. So, we're expecting the cart is going to bounce, and then stop."
And, then Newton's first law, which tells us the egg, since it's not being stopped, should continue in motion.
Student: "The momentum the cart had transferred to the egg. Since the barrier did not hit the egg, it was still in motion, and the extra momentum caused the egg to have more force as it flew off the cart.
Mike: "That sounded really good."
The third question is asking 'What happens just at the moment that the egg collides with the floor?'
Student: "It flew forward, and gravity's force pushed it down, forcing the egg to collide against the floor."
Mike: "And why is it gonna crack? It's just gonna crack because of force, right? Because the force of the, the eggshell, which is actually pushing out, is holding the egg together, is not gonna be as strong as the force of the floor.
After we've made our predictions,
"Last words on the egg?"
Mike: Then it's time to do the demonstration.
"Here's the egg; he looks completely terrified."
The joy factor is really important. If they kids are not having fun, it doesn't matter what you're talking about. They're not gonna pay attention.
"All right. Here we go. All right. Ready? 1...2...3…"
It's also fun. I mean it's just purely fun.
All: "OOHH!!" (Laughter)
Mike: "Brutal! Brutal! That one was perfect!"
I make sure that the safety part of it is also, it's hyped.
"Serious brain injuries..."
Student: "Is he alive?"
Mike: "Is he alive? I doubt it."
When we talk about why do you need to wear a helmet, the kids, they get it.
"Like, pretty massive cracks. You got some good ooze coming out of it there."
A decision like wearing a bicycle helmet, uh, is a really good one.