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# Lifting with Air

Media Type:
Video

Running Time: 1m 36s
Size: 4.9 MB

or

Source: ZOOM

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Collection Credits

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Most of the time we think very little about the air that surrounds us. Air is not a substance we automatically think of when we want to lift heavy objects -- except maybe the air we huff and puff when we lift our bodies during exertion. In this video segment, adapted from ZOOM, several cast members discover a way to lift a heavy table with little more than their own breath.

## Supplemental Media Available:

Lifting with Air (Document)

Background Essay

Lifting the weight of an entire table using a few plastic bags and the same number of drinking straws sounds completely implausible. However, the principle that makes this unlikely feat possible is the same one that enables a single person to raise a 1,500-kg (3,300 lb) vehicle off the ground using only a hand-operated hydraulic jack.

Fluids and gases confined in an enclosed space conform to a rule that physicists call Pascal's Principle. This principle, named for the 17th-century scientist Blaise Pascal, states that the pressure of a gas or a liquid in a closed, or hydraulic, system is the same at all points within the system. The principle also states that the amount of force exerted by the liquid or gas in the system is a function of both pressure and the surface area of the fluid.

According to Pascal's Principle, if you have a small and a large cylinder, such as a straw and a bag, connected together and you apply a force to the small cylinder, both cylinders experience the same pressure. However, because the large cylinder has more surface area, the force it exerts is much greater than the force applied to the small cylinder. This is because force equals pressure multiplied by area (the area over which the pressure is exerted).

This may seem a bit like getting something for nothing. But the physical world doesn't give such favors. Although the larger cylinder of the hydraulic jack seems to magically magnify the force applied to the smaller cylinder, there is a trade-off in terms of distance. For example, if the larger cylinder exerted twice the force applied to the small cylinder, it would move only half the distance. However, faced with a flat tire and no other way to lift a car, this force-for-distance trade-off is a reasonable one for most people.

Discussion Questions

• Why could the cast members lift the table this way, but if they sat under the table and blew upward, they wouldn't be able to lift it at all? What role do the bags play?
• What evidence would convince you that the air in the baggies is compressed and is therefore exerting pressure in every direction?
• What do you think would happen if the bags were made of another material such as paper or rubber?
• What are some other examples of devices that use air to lift something heavy?

• Transcript

GARRETT: Ashley of Ashland City, Tennessee, challenged us to see if we can lift things by using a resealable baggie and some straws. We're going to try lifting this table by putting a hole in the baggie, putting a straw in the hole, sealing the baggie and blowing it up like a balloon. On the count of three, we'll blow, okay? One, two, three.

GARRETT: That's so cool. Oh, mine popped. That's so awesome. Try holding it because some of the air will go out.

RACHEL: It's so far off of the table.

KALEIGH: I know, we couldn't... we could lift it up a little but we couldn't lift it up that much and look at the baggies.

GARRETT: This is so cool how air can lift this thing up.

MATT: When we blew air in the resealable baggie there wasn't a lot of space for the air to spread out and it was compressed. This means that the air was pushed together really tightly.

KALEIGH: We could tell that the compressed air was pushing hard because we had to push even harder with our breath to get air into the baggie.

MATT: We were able to lift the table because the compressed air pushed on the baggie and the baggie pushed on the table, causing it to lift. It's kind of like the tires of a bicycle. When they are flat, it's hard to ride your bike, but when you fill them up, the tires hold your weight and it's easier to ride.

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