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The fastest animal is a peregrine falcon. When it dives
through the air, it can reach a speed of over 300 kilometers
per hour. The fastest piloted plane is the SR-71A. In 1976,
this plane reached a speed of over 7,000 kilometers per hour,
Looking for something still faster? In 2005, scientists
spotted a star leaving our galaxy. The star was traveling
almost 2V2 million kilometers per hour. However, none of
these come close to the fastest thing in the universe—light.
Light travels at almost 300,000 kilometers per second.
That's faster than one billion kilometers per hour!
Light is a type of energy. It travels as waves. It can travel
through clear solids such as glass and plastic. It can also
travel through some liquids. This is why you can see your
feet when you are standing in a pool or a clear lake.
Light can travel through
solids and liquids that are
translucent. Glass and
water are both translucent.
Brick is not translucent.
Neither is melted chocolate.
Light can't travel through
bricks or chocolate. This is
why you can't see through
bricks or chocolate.
Light can also travel through
gases. You can see things all
around you because light can
travel through the air, which
is made of gases.
Light can also travel through a
vacuum—a place where there
is no matter at all.
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