[male announcer]
"T-minus 13, 12, 11, 10, 9, 8,
"go for main engine start,
6, 5, 4, 3, 2, 1,
and zero and lift-off
of space shuttle Atlantis."
How is a rocket launched
into space?
How can it push itself upwards
when there doesn't seem
to be anything to push against?
It relies on the fact
that every force
has an equal and opposite force.
This fact was first noticed
by the British scientist
Sir Isaac Newton,
who was inspired by nature
to create rules
about such forces.
One of these is known
as Newton's third law.
This law states that when
an object pushes one way--
the action--
an equal forces pushes it back
in the opposite direction--
the reaction.
The engine of a rocket
relies on Newton's third law
to propel the spacecraft
through the air.
As the fuel
inside the rocket engine burns,
it produces a hot, fiery gas.
As more gas is produced,
the pressure increases
and the gas exits
the exhaust nozzle at high speed.
The gas is pushed backwards,
away from the rocket,
and because every force
has an equal and opposite force,
as the rocket pushes
the gas downwards,
the gas pushes the rocket
upwards.
As long as the engine
keeps forcing gas
out of the bottom of the rocket,
the higher and higher
it will fly,
through the atmosphere
and all the way into space.
So it's thanks
to Newton's third law
that we have lift-off.
