Why
Do We Have Dreams?
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We have dreams because the thinking part of the
brain is wide awake even though we sleep. A dream is a kind of
experience. It seems as real as something that is actually happening; in
it the dreamer takes action and reacts. In fact the brain is more active
during dreams then it sometimes is when the body is awake.
As a reflection of a person's thoughts
and feelings, the contents of dreams are of great interest to psychologists.
They have
always wondered what our dreams actually mean.
How does glow-in-the-dark stuff work?
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You've probably seen many glow-in-the-dark toys and
wondered just how they glow. As you know, most glow-in-the-dark things
need to be charged first. You hold it up to a light and then go to a dark
place to see it glow.
In order to glow, a product must
contain a phosphor. A phosphor is a substance made up of specialized
particles that radiate (send out) visible light after being energized.
Phosphors can be charged in many different ways. Light, special types of
radiation, and even electron beams, can energize different phosphors. What
you most commonly see in glow-in-the-dark toys is either a substance called zinc
sulfide or strontium aluminates. These two substances can be charged by
light radiation and have a long persistence. The persistence of a phosphor
is the length of time it stays aglow. The major difference between these
two substances is that strontium aluminates glow for a longer period of time
than zink sulfide.
Chemists have developed thousands
of
substances that behave like a phosphor. However, no matter what the
substance, all phosphors have three common characteristics:
- They require some type of energy to
be energized.
- The color of the visible light they produce; and
- The length of time that they glow after being charged, or the persistence
of the phosphor.
Why are some people taller than others?
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Characteristic of people are mainly determined by
genetic traits passed on by close relatives. A certain person may be very
tall but have very short parents, the point is somewhere down the line this
person inherited the trait to grow very tall. The again, a very short
person may have very tall parents. It's all found in the genes.
Why is there darkness in some part of the world and not
in others?
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The earth is constantly spinning and while some parts of
the world are tilted toward the sun, others are not, leaving these areas in
darkness. While the sun provides light to the areas tilted toward the sun,
there is little light provided in the places without the sun's light. It
is also warmer in the areas with the sun's light. In the areas without the
sun's light, it is much colder.
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