CAT IN A CAR LOOKING OUTSIDE

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How do the automatic doors at a supermarket know when to open and close? How do they work?

Devices that sense your presence are either bouncing some wave off you or they are passively detecting waves that you emit or reflect. The wave-bouncing detectors emit high frequency (ultrasonic) sound waves or radio waves and then look for reflections. If they detect changes in the intensity or frequency pattern of the reflected waves, they know that something has moved nearby and open the door. The passive detectors look for changes in the infrared or visible light patterns reaching a detector and open the door when they detect such changes.

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Who was Robespierre?

Maximilien Robespierre was an important leader during the French Revolution. He was part of the Commune of Paris that overthrew Louis XVI. Under his orders, protesters were paraded and guillotined in public. On 28 July 1794, Robespierre himself was guillotined without A trial.

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Which mammals fly?

There is only one mammal that flies: the bat. Most bats are nocturnal, which means they sleep during the day and are most active at dawn, dusk, or nighttime. During the day, they sleep by hanging upside down in groups called roots. Most bats, called microbats, eat flying insects, such as moths and flies, but others eat small mammals, like mice. Some insect-eating bats can land on the ground and chase insects that live in leaf litter or dirt. One of these bats, the pallid bat, feeds on scorpions and large centipedes. Others eat fish or live on cow’s blood. The largest bats are megabats, which feed mostly on fruit.

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What do A.M. and P.M. stand for?

The initials A.M. stand for ante meridian, which is Latin for "before noon." The initials P.M. stand for post meridian, which is Latin for "after noon."

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How do you get static out of hair?

If you put a conditioner on your hair, it will attract enough moisture to allow static charge to dissipate.

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What happens to the current when it "stops"?

Current refers to moving charged particles. In most solids, the particles that do the moving are negatively charged electrons that move in the opposite direction from the way we say that current is flowing. These charged particles are the components of atoms and molecules, so they are always there inside a wire or the filament of a light bulb, even if they are not moving. Thus when the current "stops", these electrically charged particles simply stop moving. You can imagine a pipe full of water. The water can be flowing to the right or left (a current) or it can be standing still (no current). The water itself, like the charged particles, doesn't disappear when the flow stops.

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