with Answers to
Frequently Asked Questions about Classical
Physics
Why is the sky blue?
The tinier the particle, the higher the frequency of light the particle will
scatter. The atoms in the Earth's atmosphere are extremely small, which causes
them to scatter more violet light than blue light because violet is of a
higher frequency. Our eyes are not sensitive to violet light, but
they are sensitive to blue light because of the blue cones in our eyes. The blue light becomes
predominate in our vision, and we see a blue sky.
Why are you not harmed when lightning strikes your
car?
You are not harmed when lightning strikes your car because you are in a Faraday cage (unless, of course,
you are in a convertible or on the back of a truck, in which case you would be fried). A
Faraday cage is an enclosed compartment which allows a charge to reside
on its outside. The charge of the lightning is what can harm you. The electrons from a
lightning bolt mutually repel to the metal outer surface of the car.
Even though the electric field on the outside of the car is great, the net
electric field inside the car is zero because the opposing forces are balanced in
every direction.
Why does a fish appear to be closer
to the surface than it really is?
A submerged object appears to be closer to the surface than it actually is
because of refraction. The waves of light that are directed upward at an
angle toward the water surface are bent off-kilter as they speed up after
emerging into the air. They speed up because the medium through which the
waves are traveling changes. The waves that speed up reach the observer's eyes. The change in
speed from water to air dictates the path taken by the light waves. This path turns out to be
the least-time path. The person sees the fish on the same path as the
light waves that reach his eyes, which makes the fish appear closer
to the surface.
Why do you spin faster when you are
already spinning and you pull your arms in?
This is an example of conservation of angular momentum. When your arms
are extended, your rotational inertia is relativly large. As you slowly
turn, your angular momentum is the product of rotational inertia and
rotational velocity. When you pull your arms in, the rotational inertia
of your body is reduced. This causes your rotational velocity to
increase, making you spin faster.
Why is the earth round?
The earth is round because of gravitation. Masses attract
other masses, and so the earth has attracted itself together as far as it can.
All the "corners" of the earth have been pulled in. As a result, every
part of the surface is equidistant form the center of gravity, which creates
a sphere.
What is a centrifugal force?
This is an imaginary force made up by non-physics
people to explain a certain aspect of physics which they cannot explain.
It is supposed to be the force which causes a car traveling around a curve
to slide out of the curve.
What causes a car to slide out of a
curve?
Now that you know that this is not due to the imaginary
centrifugal force: While inertia is not a force, it is a
body's natural resistance to change. In this scenario, the car's inertia
is causing it to attempt to travel straight, thus resisting the curve and sliding.
What causes the interference patterns of
waves?
The interference pattern seen, when light goes through a double slit for
instance, is due to either constructive or destructive interference. If
two monochromatic waves meet in phase then there is constructive
interference; hence a bright spot seen in the pattern. If two monochromatic waves meet out of
phase, then there is destructive interference: hence a dark spot in the
pattern.
Would a pendulum's period be greater on the moon or
the earth?
The period of a pendulum would be greater on the earth because of the greater effect of gravity. The
period of a pendulum is dependent upon the formula T= (L/g)^0.5.
What is escape velocity?
Escape velocity is the velocity required for an orbiting satellite to escape from the gravitational
pull of the earth. This is determined by applying the formula V= (gr)^.5.
Why does hot water freeze faster than cold
water?
The freezing process is more pronounced in water with higher temperatures. The
reason hot water cools (and thus freezes) faster than cold water is due to
various properties of liquids. Hot water evaporates faster than cold
water. The mass loss incurred by evaporation makes cooling occur more rapidly. The other
properties are convection, dissolved gases, and conduction.
Why do mirrors reverse left and
right?
The answer is simple: mirrors do not reverse left and right. What you are
really seeing is the reversal of in and out. This is easy to explain using
a coordinate plane. Left and right are on the x-axis. Up and down are on
the y-axis, and in and out are on the z-axis. The z-axis is where reversal
of the object's image takes place.
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