Four different ways to use gears

Here are three simple gear machines made with an old construction set to illustrate a few of the ways in which we can use gears to do different jobs:

Gears for speed

In this simple gearbox, there are (from right to left) a large gear wheel with 40 teeth, a medium wheel with 20 teeth, and a small wheel with 10 teeth. When you turn the large wheel round once, the medium wheel has to turn twice to keep up. Similarly, when the medium wheel turns once, the small wheel has to turn twice to keep up. So, when I turn the large gear wheel on the right, the small wheel on the left turns four times faster but with one quarter as much turning force. This gearbox is designed for increasing speed.

Gears for force

If you power the same gearbox in the opposite direction, by turning the small wheel, I'll make the large wheel spin a quarter as fast but with four times as much force. That's useful if you need to make a heavy truck go up a hill, for example.

Worm gears

Here we are using an electric motor (the box on the right) and a long screw-like gear to drive a large gear wheel. This arrangement is called a worm gear. It reduces the speed of the motor to make the large wheel turn with more force, but it's also useful for changing the direction of rotation in gear-driven machinery.

III. Бытовые приборы

Plumbing

The plumbing system in your home is composed of two separate subsystems. One subsystem brings freshwater in, and the other takes wastewater out.

Supply Systems

The water that comes into your home is under pressure. It enters your home under enough pressure to allow it to travel upstairs, around corners, or wherever else it's needed. As water comes into your home, it passes through a meter that registers the amount you use. The main water shutoff, or stop, valve is typically located close to the meter. In a plumbing emergency, it's vital that you quickly close the main shutoff valve. Otherwise, when a pipe bursts, it can flood your house in no time. If the emergency is confined to a sink, tub, or toilet, however, you may not want to turn off your entire water supply. Therefore, most fixtures should have individual stop valves.

Water from the main supply is immediately ready for your cold water needs. The hot water supply, however, requires another step. One pipe carries water from the cold water system to your water heater. From the heater, a hot water line carries the heated water to all the fixtures, out-lets, and appliances that require hot water. A thermostat on the heater maintains the temperature you select by turning the device's heating elements on and off as required. The normal temperature setting for a home water heater is between 140 degrees F and 160 degrees F, but 120 degrees F is usually adequate and is also more economical. Some automatic dishwashers require higher temperature water, though many of these have a water heater within them that boosts the temperature another 20 degrees F.

Drainage Systems

Whether your home is on a sewer or septic system, the systems within your home are essentially the same. Drainage systems do not depend on pressure, as supply systems do. Instead, waste matter leaves your house because the drainage pipes all pitch, or angle, downward. Gravity pulls the waste along. The sewer line continues this downward flow to a sewage treatment facility or a septic tank.

While the system sounds simple, there's more to it, including vents, traps, and clean outs. The vents sticking up from the roof of your house allow air to enter the drainpipes. If there were no air supply coming from the vents, wastewater would not flow out properly and the water in the traps would need to be siphoned away.

Traps are vital components of the drainage system. You can see a trap under every sink. It is the curved or S-shape section of pipe under a drain. Water flows from the basin with enough force to go through the trap and out through the drainpipe, but enough water stays in the trap afterward to form a seal that prevents sewer gas from backing up into your home. Every fixture must have a trap. Toilets are self-trapped and don't require an additional trap at the drain. Bathtubs frequently have drum traps, not only to form a seal against sewer gas but also to collect hair and dirt in order to prevent clogged drains. Some kitchen sinks have grease traps to collect grease that might otherwise cause clogging. Because grease and hair are generally the causes of drain clogs, traps often have clean-out plugs that give you easier access to remove or break up any blockage.

IV. Авиация