Ch. 9.1 Fluid Systems

Popcorn!• Why does popcorn pop?– believe it or not, this has to do with water– each kernel of popcorn contains a small amount of

water, stored in the soft, white starch– a hard casing surrounds the whole kernel

Popcorn!• Why does popcorn pop?– when the kernel of popcorn is

heated, the water turns to steam– since this steam is a gas, it occupies

more space than the liquid water– this results in increased pressure

inside the kernel– when the pressure created inside by

the steam becomes too great for the kernel to contain, the kernel explodes

– the steam escapes and the kernel is turned inside out

video

Popcorn!• Why do some kernels in a bag of popcorn

remain un-popped?!?!– kernels will remain un-popped if the hard casing of

the kernel has a small crack or hole– this allows the steam to escape while it is heated,

not allowing the pressure inside the kernel to increase

– also, if a kernel is allowed to dry out, there will not be enough water inside the kernel to make steam

Popcorn!

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Fluid Systems• fluid system – a group of parts, including at

least one fluid, that interact with each other and function together as a whole– natural fluid systems include: our body’s

circulatory and respiratory systems, the movement of sap in a tree, and the movement of starfish

Pascal’s Law• Pascal’s Law – states that when a force is

applied to an enclosed fluid, the increase in pressure is transmitted equally to all parts of the fluid– proposed by Blaise Pascal,a French mathmetician, philosopher, and physicist inthe 1600’s

Keeping in the Pressure

• for a fluid system to work properly, the entire system must be completely sealed

• even the smallest hole or leak can cause the system to fail

Hydraulic Systems

• hydraulic systems – systems that use liquid under pressure to transmit a force and do work

Liquids Cannot Be Compressed

• liquids cannot be compressed by ordinary means– when pressure is applied

to a liquid in a pipe or tube, the force can be transmittedover a distance• when you turn on the spicket,

water comes out the hose• this property is useful in

transporting water or oil in pipelines

Multiplying Forces

• hydraulic systems can multiply the force exerted by a liquid

• hoist – a fluid system that uses two pistons of different sizes to create pressure to lift a vehicle

• piston – a disk that moves inside a cylinder

Hoists

• the small piston is the input piston, which pushes down on the liquid to create pressure

• this pressure is then transmitted through the liquid, where it pushes up on the large piston

• the large piston is the output piston

Pneumatic Systems

• pneumatic system – a system that uses a gas, usually air, under pressure to transmit a force

Pneumatic Systems

• in order for a gas to be used in a pneumatic system, that gas must first be compressed

Advantages of Pneumatic Systems

• safer – the device does not create sparks within the system

• price• more reliable over a larger temperature range

than hydraulic systems (this is especially important in Canadian winters)

Pumps• pump – a device that moves a fluid through or

into something– examples: a bicycle pump moves air into the tires

of your bike; your heart pumps blood throughout your body

Archimede’s Screw Pump

• uses a screw, or an inclined plane wrapped around a shaft, to move water up an incline

Valves• valves – devices that control the flow of fluids– examples: handles on a faucet control the amount

of water flowing out of the faucet; there are many valves in your body that allow the flow of blood in only one direction

Ball Valve

Butterfly Valve

Needle Valve

One-Way Valves

The Toilet – A World of Valves