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Thrust
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{{otheruses}}
'''Thrust''' is a reaction
force (physics) force described quantitatively by
Isaac Newton Newton's
Newton's laws of motion Second and Third Law. When a system expels or
acceleration accelerates mass in one direction the accelerated mass will cause a proportional but opposite force on that system.
Mathematically this means that the total force experienced by a system accelerating a mass ''m'', is equal and opposite to the mass ''m'' times the acceleration ''a'' experienced by that mass:
:''F = m·a''
Examples
Image:aeroforces.jpg thumb|250px|Forces on an aircraft
An
aircraft generates forward thrust when the spinning
propellers blow air, or eject expanding gases from a
jet engine to the back of the aircraft. The forward thrust is proportional to the (
mass of the air) multiplied by (average
velocity of the airstream).
Similarly, a
ship (or reverse thrust) when the propellers are turned to accelerate water backwards (or forwards). The resulting thrust pushes the ship in the equal and opposite direction to the sum of the
momentum change in the water flowing through the propeller.
A
rocket (and all mass attached to it) is propelled forward by a thrust force equal to, and opposite of, the time-rate of momentum change experienced by the exhaust mass accelerating out from the combustion chamber through the rocket nozzle. This is the exhaust velocity with respect to the rocket, times the time-rate at which the mass is expelled. Of course, for a launch the thrust at lift-off should be more than the weight, and with a fair margin, because a "slow launch" would be very inefficient.
Each of the three
Space shuttle main engines can produce a thrust of 1.8
meganewton MN, and each of its two
Space Shuttle Solid Rocket Booster Solid Rocket Boosters 14.7 MN, together 34.8 MN. Compare with the mass at lift-off of 2,040,000 kg, hence a weight of 2.0 MN.
The
simplified Aid for EVA Rescue (SAFER) has 24 thrusters of 3.56 N each.
See also
*
Gimbaled thrust, the most common thrust system in modern rockets
*
Thrust-to-weight ratio
*
Thrust vectoring
Category:Aerodynamics
Category:Force
de:Schub
es:Empuje
fa:رانش
fr:Poussée
it:Spinta
he:דחף (כוח)
ja:スラスト
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