So motion need not be explained by the
continuing force of a prime mover. He drew a graph of distance
versus time for the rolling ball, which indicated that the
distance traveled was a square of the time elapsed. He realized
that the movement of a projectile involved a horizontal and a
vertical component and guessed that the effects of falling were
independent of the horizontal motion. He demonstrated that a
projectile follows a path of a parabola, instead of a straight
line, and that it too descends a distance which is the square of
the time taken to fall. That is, a thrown object will strike the
ground in the same amount of time as an object simply dropped from
the same height.
The telescope was invented in 1608. The next year, Galileo built a
greatly improved telescope using a lens to look at the skies. He
observed that the surface of the moon had mountains, valleys, and
craters much like the earth, and was illuminated by reflected
light. He noticed that the planet Jupiter has moons orbiting it.
He noted that the planet Venus progresses through phases similar
to those of the moon orbiting the earth and that it was very large
with a crescent shape or very small with a round shape. This
apparent change in size could only be explained if Venus revolved
around the sun, rather than around the earth. Thus more credence
was given to the Copernican theory that the earth and all planets
revolve around the sun, so Galileo was denounced by the church.
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