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Isnin, 25 Mei 2009

Bagaimana roket H2O boleh terbang?

Terdapat beberapa daya yang bertindak ke atas roket h2o yang perlu diketahui iaitu sebelum, semasa dan selepas penerbangan. Tapi penerangannya dalam bahasa inggeris:

What makes a rocket fly? Of course, it is the pressurized air
inside the rocket that propels it upwards, but why does adding
water increase the height of the rocket? And how does the size
of the nozzle affect the rocket? To answer these questions, we
must look at the forces which affect the rocket during its flight.

When the rocket is sitting on the launch pad, the nozzle of the
rocket typically fits over some type of rubber or metal stopper,
called a “launch rod.” For the first few tenths of a second, all of
the rocket’s propulsive forces are generated by the pressurized air
pushing against the launch rod. This pushes the rocket upwards,
until the rocket lifts off the launch pad. We call this the “launch
rod reaction force.”

When our rocket has cleared the launch pad. We no longer have a
launch rod reaction force, but our propulsion now comes from
the water inside the bottle. The pressurized air pushes against
the surface of the water, causing the water to be expelled through
the nozzle of the bottle. This creates a propulsive force, pushing
the rocket upward.

Newton’s third law of motion states: “For every action there
is an equal, but opposite, reaction.” In this case, our action is
the expulsion of the water out of the nozzle, and our reaction is
the propulsive force on the rocket generated by our action.

After all of the water has been propelled out of the rocket, the
“air pulse” occurs. The air pulse is caused by the remaining air
pressure in the bottle leaving through the nozzle, much like the
water did earlier. This force is not nearly as great as the one
generated by the water, but it is important to consider it.

From this point on, our rocket no longer has any propulsive forces.
Since it already has so much speed built up, it continues travelling
upward, until the forces of drag and gravity finally bring the
rocket to a stop. The point at which the rocket’s velocity is zero
is called “apogee.”

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