Recommended for: Grades K-8
Resource: Lifting with Air
Media Type:
QuickTime Video
Length: 1m 36s
Size: 2.2 MB
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 (PDF Document)
Teachers' Domain, Lifting with Air, published January 22, 2004, retrieved on ,
http://www.teachersdomain.org/resource/phy03.sci.phys.matter.zlift/
- Background Essay
- Questions for Discussion
- Standards
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.
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.
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Source: ZOOM
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