What keeps them up?
How do an airplane’s wings help it stay in the air? What keeps a
satellite up?
Airplane wings have a special shape. They are curved on top and straight
on the bottom. This shape is what helps lift the plane up.
When the plane starts to move, the wings cut through the air. The air
moves over the curved top of the wing and under the straight bottom. The
air moving over each wing pushes down on it. And the air moving under
each wing pushes up.
The curved top of the wing is longer than the straight bottom. The air
moving over the wing has to travel farther than air moving under it. So
the air going over the wing moves faster. And the faster it moves, the
less it pushes. As the push over the wing gets weaker, the push
under the wing begins to lift the plane. So the plane leaves the
ground. As long as the plane keeps moving, the wings lift it and help it
to fly.
Far out in space, a satellite circles the earth. What keeps it from
falling? And what keeps it from sailing away?
Two kinds of forces work to make the satellite circle around the earth.
One is the tremendous push of the satellite’s speed— thousands of
miles (kilometers) per hour. Without this push, gravity would pull the
satellite back to earth.
The shape [ot]{.smallcaps} me wings helps an airplane to fly.
The other force is the pull of the earth’s gravity, which reaches far
out into space. Without this pull, a satellite would travel in a
straight line, away from the earth.
Gravity pulls the satellite toward the earth. But the speed of the
satellite pushes it outward. When the push and the pull are even, the
satellite can’t sail away from the earth—or fall back to the earth,
either. Instead, it speeds around the earth, making a circle in space.
