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# Designing a Puff Mobile

Media Type:
Video

Running Time: 3m 22s
Size: 10.1 MB

or

Source: ZOOM

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If you were to build a vehicle powered by your breath, what characteristics would increase or decrease its performance the most? In this video segment adapted from ZOOM, four cast members design, construct, and test a variety of puff mobiles.

## Supplemental Media Available:

Designing a Puff Mobile (Document)

Background Essay

In order for a vehicle of any type to move, it must produce or harness a force strong enough to overcome the resistance of friction or drag. Most vehicles rely on internal power sources to convert energy into a force that propels them forward. However, some vehicles, including sailboats, use the wind's energy to generate the force that makes them move.

Wind can move a vehicle forward if, and only if, the force it applies to the vehicle is enough to overcome forces like friction and drag that resist forward motion. To make this possible, wind-vehicle designers can try to increase the force that moves the vehicle forward, or reduce the resistant force. Often they do both.

For example, when traveling with the wind, sailors typically use sails large enough to capture as much wind as possible, but not so large that they make the boats they're attached to unstable. If large enough, a sail can capture enough wind to propel a boat forward nearly as fast as the wind itself. Ironically, sailors can travel even faster than the prevailing wind speed by sailing at angles that oppose the wind somewhat. In so doing, they use not only the force of the wind on the sails but also the force of the water on the boat's hull and either its keel or center board (depending on the type of boat) to propel the boat forward.

Reducing friction across the ground or reducing drag through water or air is another way to increase the performance of vehicles. Wheels are probably the best way to minimize friction on land. Rather than dragging and scraping across the ground, automobiles roll on wheels -- so easily, in fact, that a person can push a car to a gas station, if necessary. Likewise, the hull of a boat and the fuselage of an airplane are designed to cut through water and air with a minimum of drag.

Discussion Questions

• What is the source of energy that makes the puff mobile move?
• What forces slow down the puff mobile?
• Which design features are the most successful on the puff mobile? Explain why.
• Do you think these puff mobiles would work as well if you tested them outdoors? Explain your answer.

• Transcript

VOICE: (gasps) Ooh!

MIKE: Anna Y. of Houston, Texas, wrote to tell us about a puffmobile competition her class had. A puffmobile is a vehicle made out of straws... Lifesavers... paper... paper clips... and tape.

KORTNEY: To make your puffmobile move, you can only blow on it. That's why it's called a puffmobile. Anna told us that a boy in her class got his puffmobile to go nine feet.

GARRETT: We're going to design our own puffmobiles. Caroline and I will be one design team, and Mike and Kortney will be the other.

CAROLINE: After we're finished building, we're going to have a contest to see whose puffmobile can go nine feet in the fewest amount of puffs. So, let's get set up.

GARRETT: We don't have to use all of this material.

CAROLINE: Yeah, let's see, if we only use, like, paper and tape...

GARRETT: What if we fold it in kind of like a tube and then blow on...

CAROLINE: I think there's, like, a way to do that.

MIKE: We could make the frame out of these and then just put paper on top and then just blow it.

KORTNEY: So it might weigh... it might weigh it down.

MIKE: Yeah, you're right. But if we don't weight it enough, it might fly off course. So I'll make a frame.

KORTNEY: I'll see what shape will probably be easiest.

CAROLINE: You want to test it out? Yeah, I'll just try, just to see if it works.

GARRETT: Okay. Ooh, it goes.

MIKE: We need to have the most amount of area we can to blow, but we also need the least amount of friction and we need it to be the most aerodynamic that we can.

GARRETT: Wait a minute, what if we add... wait. What if we add weight to the sides? Because it seems like... It's, like, flimsy. If we add weight to the sides, it might hold it down and stay on the ground a little bit more.

CAROLINE: How do you think we could add weight?

GARRETT: By, uh, putting on paper clips.

KORTNEY: I think it's a little too heavy.

MIKE: I think if we just did two.

KORTNEY: With two, you can make it like skis and just have the paper...

MIKE: Oh... like this? Yes, yes. Actually, that might work really well.

CAROLINE: Okay, let's try something totally different.

GARRETT: I think if we fold a piece of paper and then make kind of like a car structure with... with straws and lifesavers. And then, you'd take your piece of paper, you'd take your two straws, and then you'd tape it to the front. And then you'd have a support... you'd have a support straw going in the middle.

MIKE: If we made more of a tube... it'd be a lot more aerodynamic.

KORTNEY: Let's just try that and then blow it.

MIKE: Here, I got tape.

KORTNEY: I mean, tape it.

GARRETT: So then a straw that goes...

CAROLINE: Oh, that is so cool.

GARRETT: Right there.

CAROLINE: I think it's going to work really well. Go! That's good-- one. Two... Three... Four, good job.

MIKE: Oh, no!

KORTNEY: We got to get it in three, Mike. Whoo, three, good job. When we blew on our puffmobile, we created wind, which is moving air. It then pushed on our puffmobile and made it move.

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