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Air Power: Making a Hovercraft

Resource for Grades K-8

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Media Type:
Video

Running Time: 3m 31s
Size: 10.6 MB

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Source: ZOOM

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Air Power: Making a Hover Craft (Document)

Air Power: Making a Hovercraft (en español) (Document)

Accessibility Features: Caption, Transcript

Background Essay

Friction is defined as the resistance to sliding motion between two surfaces in contact -- a solid object rubbing against another solid, or a solid object moving through a gas or liquid. In some situations friction can be useful, for example, a brake pad rubbing against a wheel rim slows a moving bicycle. However, in many other situations friction causes problems and needs to be reduced. Solid, plastic, or liquid materials called lubricants are used to reduce the effects of friction. Petroleum jelly, motor oil, and the ball bearings contained between a wheel and its axle are examples of common lubricants.

Hovercrafts work on two main principles: lift and propulsion. A fan blows air straight down underneath the vehicle. A skirt -- a piece of material fastened around the bottom edge of the base of the vehicle -- traps the air between the vehicle and the ground or water. As the fan continues to blow, the air pressure inside the enclosed space increases. Under pressure, molecules try to spread out, and when prevented from doing so, they exert a force on the surfaces that contain them. If the air pressure inside the skirt rises so much that the air molecules exert a force greater than the downward force produced by the weight of hovercraft, it lifts the vehicle. The cushion of air between the ground or water and the vehicle acts as a lubricant. In simple configurations where a great deal of force is not required, adequate pressure can be attained without a skirt.

Some hovercrafts have two engines that drive separate fans: one to generate lift, the other to generate thrust, which propels the vessel forward. Integrated lift-propulsion systems use only one engine to perform both functions.

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Discussion Questions

How did the cast know that air was being pushed under the plate if they couldn't see it?

If you used a bigger balloon, do you think the hovercraft (plate) would be easier or harder to move? Explain your reasoning.

Where does the air come from in a real hovercraft, such as the one moving over the grass in the video segment?

Why do you think that the hovercraft was invented? In what situation would it be a good choice for a vehicle?

What are some of the important design features in a hovercraft?

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Transcript

(bubbling) (fan humming)

SHING YING: This is a hovercraft. It floats on a cushion of air that's been created by fans. People ride around on this hovercraft for fun. Here's what a hovercraft might look like in the future. In 'Star Wars', instead of cars, people use hovercraft for transportation.

ALINE: And here's a hovercraft that you can make. Oh, my goodness.

SHING YING AND ALINE:(both giggle).

SHING YING: Melissa F. of Shoreline, Washington, and Josh G. of Merriam, Kansas, sent us the idea.

ALINE: So, here's what you'll do to make one. First, take a ball-point pen and poke a hole in the center of a film canister. And I already poked my hole. Then do the same thing to a plastic plate, see? Mine is already there.

SHING YING: Put the film canister over the hole in the plate and use poster putty to stick it on like this. Okay, you want to help me?

ALINE: Sure.

SHING YING: It's a little bit hard to rip.

ALINE: Glue is like glue.

SHING YING: Okay. It helps if you make a log roll, and then just circle it around. Like this. Yep, okay.

ALINE: Put both things right in the center.

SHING YING: Oh, so the air can come through and keep it compact.

ALINE: Okay, that looks good. Then blow up a balloon and put it over the film canister.

SHING YING: Do you want me to try?

ALINE: Sure. That looks good.

SHING YING: Twist the opening of the balloon so that you don't let any air out. Then stretch it over the film canister. Okay, make sure the opening of the balloon lines up with the hole in the film canister.

ALINE: Then put your hovercraft on a smooth, flat surface, like this table. Then give it a flick. It's floating on air. You just can't see it. If I go like that...

SHING YING: You still can't see it.

ALINE: Because it's so thin. It's really cool.

SHING YING: Here's the science scoop for how this hovercraft works. Our hovercraft moves because it's floating on a cushion of air. The air has to go somewhere, so it floats out of the balloon and under the plate. The layer of air under the plate takes up space, so it keeps the plate and table from rubbing against each other.

ALINE: See, if I push this plate when there's no air underneath it, it doesn't go very far. This is because of friction. Friction is a dragging force which occurs when two objects slide against each other, but the hovercraft doesn't have very much friction because it rests on air.

SHING YING: It's like an air hockey game. When you turn the game on, air comes through these holes. The puck is able to rest on air, so there's very little friction. (game humming)

ALINE: Good job!

SHING YING: Thanks. Okay. But when you turn the game off, there's no cushion of air, so the puck isn't able to float across the board.

ALINE: Experiment with hovercrafts at home. Change one thing, like the size of the balloon, the type of plate or the size of the hole in the plate. These are the variables. Predict what you think will happen and test it out.