1. An electric car is powered by ___.
a) an electric motor b) a diesel engine c) an internal combustion engine
2. Batteries are recharged ___.
a) only at service stations b) from another car c) from household electric grid
3. Recharging a battery now takes ___.
a) little time b) much time c) much work of many people
Text 9. How Bearings Work?
Active Vocabulary:
| bearing | підшипник | storage | зберігання |
| to spin | обертатись | in excess of | понад |
| smoothly | плавно | revolution | оберт |
| to wear (wore, worn) | зношуватись | to melt | плавитись |
| friction | тертя | to explode | вибухати |
| to slide | ковзати | to handle | мати справу з чимось |
| to cause | викликати | log | колода |
| to reduce | зменшувати | to withstand | витримувати |
| flywheel | махове колесо | concave | угнутий |
Have you ever wondered how things like inline skate wheels and electric motors spin so smoothly and quietly? The answer can be found in a neat little machine called a bearing.
The bearing makes many of the machines we use every day possible. Without bearings, we would be constantly replacing parts that wore out from friction.
The concept behind a bearing is very simple. Things roll better than they slide. The wheels on your car are like big bearings. If you had something like skis instead of wheels, your car would be a lot more difficult to push down the road. That is because when things slide, the friction between them causes a force that tends to slow them down. But if the two surfaces can roll over each other, the friction is greatly reduced.
Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers “bear” the load, allowing the device to spin smoothly.
There are several types of bearings, and each has its own interesting uses, including magnetic bearings and giant roller bearings.
Magnetic Bearings. Some very high-speed devices, like advanced flywheel energy storage systems, use magnet bearings. These bearings allow the flywheel to float on a magnetic field created by the bearing. Some of the flywheels run at speeds in excess of 50,000 revolutions per minute (rpm). Normal bearings with rollers or balls would melt down or explode at these speeds. The magnetic bearing has no moving parts, so it can handle these incredible speeds.
Giant Roller Bearings. Probably the first use of a bearing was back when the Egyptians were building the pyramids. They put round logs under the heavy stones so that they could roll them to the building site. This method is still used today when large, very heavy objects like the Cape Hatteras lighthouse need to be moved.
Earthquake-Proof Buildings. The new San Francisco International Airport uses many advanced building technologies to help it withstand earthquakes. One of these technologies involves giant ball bearings. The 267 columns that support the weight of the airport each ride on a 5-foot-diameter (1.5-meter) steel ball bearing. The ball rests in a concave base that is connected to the ground. In the event of an earthquake, the ground can move 20 inches (51 cm) in any direction. The columns that rest on the balls move somewhat less than this as they roll around in their bases, which helps isolate the building from the motion of the ground. When the earthquake is over, gravity pulls the columns back to the center of their bases.