Why does only one side of the car have a mirror that says "objects may be closer than they appear"

Many cars have a mirror on the passenger side that is curved to provide a wide angle view. This is so that the driver can see a car in the blind spot (which is worse on the passenger side of the car). The downside of this mirror is that it gives the impression that objects are farther away than they really are. It is decided that the danger of not seeing a car in the blind spot outweighs the danger of mistaking the distance of the car. Most people can learn to adjust to the distorted distance perception anyway. However, on the driver's side, it is more important to provide an undistorted view, so a standard flat mirror is used.

Why are Power Lines High Voltage?

This is a good question because we know high voltage lines can be dangerous to people. Why not use low voltage power lines?

The amount of power that is delivered through an electric power line is the product of the voltage and current going through it (Power = Current x Voltage). Thus, high power transmission can be achieved by having either high current or high voltage.

However, a small amount of this power is lost through heating of the power line due to its resistance. The amount of power dissipated by the transmission line is proportional to the current going through it and the square of the resistance (Power Loss = Current x Resistance x Resistance). In order to minimize the heating of the power line, the current must be kept to a minimum.

Therefore, the best way to deliver the most power, and keep loss to a minimum, is to have a high voltage and a low current.

Why is staring at the sun bad?

Why do people tell kids not to look at the sun, when the body's natural reaction is to look away anyhow?

It is true that the human body naturally reacts to bright light. However, when staring at the sun, this is not always the case. It is especially dangerous during an eclipse because the illumination is less, reducing your tendancy to look away.

The most common injury to the eye from looking at the sun is a retinal burn. The retina has no pain recepters, so you will not realize that you are damaging your eye until it is too late. As a person stares at the sun, the sun's image on the retina is heating up and the retina may become severly burned.

Apparently kids are at the greatest risk for retinal damage(http://www.drgreene.com/21_169.html). Tell your kids to imagine what happens when they hold a magnifying glass up to a piece of paper. If it is held there too long, the paper gets burned. The lens of your eye is like a magnifying glass, and you don't want to burn your retina!

Warning, techno-babble: Unlike a light bulb, which is an extended source, the sun is acts like a point source, which means that the light will be more focused on your retina causing greater risk of damage. However, because the sun is a point source, you can easily "view" the sun, or a solar eclipse by using a pin-hole camera. One simple trick I used during a solar eclipse was to criss-cross my fingers between my hands and look at the shadow on the ground. I could see an image of the sun on the ground through every space between the shadows of my fingers.

Remember, the only safe time to stare at the sun is at night!

What is a laser?

I'll start things off by asking the first question myself... what is a laser?

A laser is a light source that exhibits several properties that make it unique compared to other types of light sources (incandescent and fluorescent light bulbs, the sun, etc).

1. Laser light is monochromatic - this means that the light that comes from a laser is a single wavelength (one color). This is why you usually see red or green lasers, for example, and not white lasers. The color white is a combination of many colors.
2. Laser light is coherent - this means that all the light "waves" are organized with respect to each other. Think of this like synchronized swimming, whereas most other light sources are more like the random collection of people swimming down at the local pool.
3. Laser light is directional - ...hence, the laser beam. Whereas, your typical light bulb emits light in all directions.

These properties of lasers make them extremely valuable tools for many applications including metrology (precise measurements), remote sensing, industrial processing, medical procedures, and, of course, the all-important laser light show.