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Introducing Physics
The force of gravity is a basic aspect of physics. Scientific tests of
the effects of gravity have long proven that the acceleration of an
object falling through the atmosphere is about thirty-two feet (9.8
meters) per second. Newton believed gravity worked because ev-
ery object has a degree of attractive force on every object around
it. The more massive the object is, the greater the force of the at-
traction. The Earth, being the most massive object around, exerts a
very strong force on the objects that sit on its surface. Astronomers
believe the force of gravity on other planets can be calculated by
comparing the size of those planets to the Earth. We can see from
watching the leaping antics of humans on the moon that a gravi-
tational force draws the people back to the surface, or else when
they jumped they would have flown off into space, never to be seen
again.
blow was the result of a vicious attack, clearly meant to harm the victim.
Physics proved that Bell was lying.
Think about this for a moment: a tennis ball dropped from the top of New
York City’s Empire State Building, which stands 1,453 feet (443 meters)
high, falls for about 9.5 seconds before it hits the ground. At the moment it
hits the ground, the ball will be moving along at about 305 feet (93 meters)
each second, or approximately 208 mph! Why is the ball moving so fast?
Most people quickly answer: gravity. But what is gravity, and how can we
predict the speed the ball will reach during the fall? The answer is simple:
we use our knowledge of physics.
