What is Thrust: Definition and 344 Discussions

Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that system.
The force applied on a surface in a direction perpendicular or normal to the surface is also called thrust. Force, and thus thrust, is measured using the International System of Units (SI) in newtons (symbol: N), and represents the amount needed to accelerate 1 kilogram of mass at the rate of 1 meter per second per second. In mechanical engineering, force orthogonal to the main load (such as in parallel helical gears) is referred to as static thrust.

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  1. M

    Find Thrust on Cube Half-Filled w/ Water & Oil

    Homework Statement A closed tank in the shape of a cube of side root 2 is half full with water and half with oil of relative density 1.2. The tank is placed on a horizontal table and is then tilted about one edge until the faces about this edge are inclined at 45 degrees to the horizontal. See...
  2. Jonnyb42

    Illuminative Thrust: Can Light Provide Measurable Propulsion?

    If light has momentum, is it possible to have an intense enough "flash light" to provide measurable thrust?
  3. N

    Static equilibrium thrust bearings

    Hi all, I have a question regarding thrust bearings. For my statics class we've been tasked with finding equilibrium forces for a modular band saw. The thing I'm having trouble with is the many bearings in the part. My only question is that if the only known given force is tension in a pulley...
  4. B

    Deriving Thrust from Newton II for Rocket Motors

    Homework Statement Derive from Newton II the thrust (the force produced by the rocket exhaust) achieved by a rocket motor which ejects material with constant velocity u and mass ejection rate a. Homework Equations The Attempt at a Solution Not sure...I know how to derive vf =...
  5. A

    Is the Thrust Problem on an Airbus A320 Jetliner Unsolvable?

    Homework Statement An airbus A320 jetliner has a takeoff mass of 75,000 kg. It reaches its takeoff speed of 82 m/s in 35 s. What is the thrust of the engines? You can neglect air resistance but not rolling friction. (The force of rolling friction is given by Fr = \mur N Homework Equations...
  6. A

    Calculating Needed Thrust for a Moon Landing

    Homework Statement A landing craft of mass 12,000 kg prepares itself for a Moon landing. When at a vertical distance 160m above the Moon’s surface it’s downwards velocity is 15 m/s. A retrorocket is fired to give the craft an upward thrust to slow its speed to zero as it meets the...
  7. A

    Orbital Mechanics - effect of thrust on v, R, a

    Homework Statement A spacecraft orbits around the Earth at a tangential speed v and a radius R, in accordance with the equation a_{c} = \frac{v^{2}}{R} . a) If the spaceship's engines exert a force parallel to its instantaneous vector of motion, what is the effect on the quantities...
  8. T

    What is the flow velocity of a rocket engine's thrust chamber?

    Hello. I am trying to find the thrust chamber flow velocity for a rocket engine, but no literature seems to be able to come up with a solution for this. The best I have found is "Rocket Propulsion Elements" which states that the value probably lies somewhere between 200-400 ft/sec. But in...
  9. M

    Simple thrust measurement stand

    I have a thrust producing engine and I would like to measure the thrust from it as accurately as possible without needing the use of scales, rollers, load cells, etc. Anyway a friend of mine suggested I suspend the engine from four wires so that the wires are vertical when the engine is...
  10. K

    Formula for thrust force on helicopter

    can anyone please give me the formula to calculate the thrust force exerted by the rotor blades of the helicopter on the air
  11. Z

    Minimum thrust of engines at lift-off

    Homework Statement Hi there Rocket has a total mass of 3.4 x 10^6 kg at lift-off. The first stage contains 2.0 x 10^6 kg of propellants which is consumed at a rate of 1.4 x 10^4 kg s Find the minimum thrust of the engines at lift-off? I would have thought that you needed one more...
  12. E

    How to Calculate Thrust for an Airplane Takeoff?

    Homework Statement An Airbus A320 jetliner has a takeoff mass of 75,000 kg. It reaches its takeoff speed of 82 m/s in 35s. Homework Equations F=ma V/t=a The Attempt at a Solution I am completely lost on this question. I have seen numerous examples on the internet, with the exact...
  13. M

    Why is the thrust force equal to the change in momentum of the rocket?

    Hello People actually i want to make sure of this explanation The external force acting on the rocket is zero Therefore : F = mdv/dt+vdm/dt=0 Therefore mdv/dt=-vdm/dt=Fimp(Impulse force or thrust force) Well I have an explanation for this but I'm not sure about it The external...
  14. O

    Solving for Lunar Landing Craft Thrust

    Homework Statement A 8.73 × 103-kg lunar landing craft is about to touch down on the surface of the moon, where the acceleration due to gravity is 1.60 m/s2. At an altitude of 217 m the craft's downward velocity is 16.5 m/s. To slow down the craft, a retrorocket is firing to provide an...
  15. G

    Why Single Direction Thrust Ball Bearings Can Only Be Used in One Direction

    This isn't a homework question, but something I'm interested to know that my engineering corespondance doesn't mention. I'm aware there is both single direction and double direction thrust ball bearings but can anyone tell me why can a single direction thrust ball bearing only be used in one...
  16. A

    Pulse Jet Propeller Thrust Calculation

    Hello everyone! I recently visited the Air Force museum in Ohio and saw their Pulsejet Helicopter. It was intriguing how they attached a pulsejet to the end of each propeller tip. Since then, I’ve been wondering if two pulsejets could be used on a general aviation propeller. I’d like to...
  17. E

    Calculating Thrust of a Rocket

    I am usually bad with calculations, so please help me out. It's not a homework, merely my interest... So, let's say I have a tube with some air pressure in it and I open up one end of the tube so the pressurised gas exits it in one direction... (basically a rocket) Pretty simple, huh? :D...
  18. M

    Child jumps on a cart, cart slows down, find mass of the cart and thrust force

    Homework Statement A cart is driving on straight tracks with a velocity of 2 m/s. In the opposite direction, with an angle of 60º according to the tracks, a child with a mass of 2 kg is running with a velocity of 2m/s, he jumps on the cart and stays there. - Find the mass of the cart, if its...
  19. J

    How Much Thrust Does a 1W Flashlight Emit?

    What would be the thrust from a 1W light output flashlight, assuming light is not scatered at all. I'm not sure but if it depends on the wavelength, assume it only emits 500nm light. and if I were to put a perfect mirror right infront of this flashlight would the mirror receive the same...
  20. wolfspirit

    Calculating Thrust for Rocket Weight & Altitude

    This is my first posting - I don't know whether its on the right section but I have a question is there a formula to work out how much thrust you need to get a certain weight of rocket up in the air, also for the rockets altitude? Thanks
  21. P

    Rocket Thrust Balancing Gravity

    Homework Statement A rocket (initial mass m0) needs to use its engines ot hover stationary, just above the ground. If it can afford to burn no more than a mass (lamda)m0 of its fuel, for how long can it hover? If the exhaust velocity is 3000 m/s and lambda is 10% how long can the rocket...
  22. C

    How Is Thrust Calculated for a Jet Engine in a Lab Test?

    Homework Statement A jet engine is being tested in the laboratory and it is found to consume 20 kg of air per second while using 0.2 kg of fuel per second. Given that the exit velocity of the gases is 500 m s-1, calculate the thrust generated by the engine. Homework Equations F = M(V-U)...
  23. B

    Calculating Average Thrust Force for Airplane Take-off

    Homework Statement The take-off speed of a given airplane is 250 mi/h. If the take-off weight is 110,000 Kg, what is average the thrust force exerted by the engines? Homework Equations w=mg ,F=ma , F=mW The Attempt at a Solution the mi/h confuses me and I don't know which...
  24. S

    Resultant thrust and overturning turnning moments

    Homework Statement A vertical sluice gate is 5 meters wide and 3 meters deep. calculate the resultant thrust and overturnning moment when the water is level with the top edge of the gate. Density water = 1000kg/m^3 Homework Equations Newton's First Law F = ma Moment = Force x...
  25. T

    What is the equation for approximating propeller thrust at a known RPM?

    Is there some equation i can use in order to approx. find the trust created by a prop at a known RPM?? -Tom
  26. P

    Hydrostatic Thrust Calculation for Trapezoidal Retaining Wall

    Homework Statement A trapezoidal mass concrete retaining wall 6m high,1.5m wide at the top and 3m at the base retains water to its full height. calculate the hydrostatic thrust on the retaining wall and a factor of safety against oveerturning. take the density of water to be 1000kg/m3 and the...
  27. K

    Thrust needed for Orbit of a satellite

    Homework Statement A satellite is fitted with a station keeping rocket capable of producing thrust of 500N. Its speed is 500Km/hr. Mission control wishes to increase the radius of orbit by a factor of 0.5. For how long should the rocket be fired to achieve this? (The weight of the satellite...
  28. Q

    Centripetal thrust need at high-speed

    Hi Relativists My puzzle is inspired by Stephen Baxter's novel "Ring" in which the starship "Great Northern" flies out and back to Earth in a proper time of 1,000 years, but on Earth 5,000,000 years have passed. The description in the novel suggests that the starship flies in a loop, so I...
  29. jhae2.718

    Practical examples of fludic thrust vectoring

    This may be more relevant to aero than general mech e, but since it has to do with propulsion I figure that this is the best section to post this. Does anyone here know of any practical example of a fluidic thrust vectoring engine for aircraft? From research all I have been able to...
  30. P

    Helicopter tail rotor thrust requirement

    How can you calculate the amount of thrust needed by the tail rotor of a helicopter to counter the torque of the main rotor?
  31. E

    Propellor Thrust Calculations for P-51 Mustang Simulation

    Hello everyone This is my first post. I am currently making a simulation of a P-51 Mustang in Blender3d. ("www.blender.org"[/URL]) as the other ones are from the Wright section of the NASA website as well. If someone could explain these in simple terms for me (as I am only a tenth Grader) (or...
  32. V

    Calculate Jet Engine Net Thrust (F(N))

    I was given some notes on aircraft performance that states the equation for finding the net thrust of a jet engine. ---------------------------------------------------- It states (words in brackets are subscripts): F(N) = m dot (air) + m dot (j) V(j) - m dot (air) V F(N) = net thrust...
  33. Y

    Thrust calculation for hovercraft

    hello to u all out there (sorry for the misspelling, english is not my native language) i'm mechanical engineering student and I'm working on my final project which is design of a light hovercraft (acv). i was wondering how do i calculate the power needed to make it go forward.?? do i...
  34. H

    What's the purpose of thrust balance in Turbo Fan Engine?

    What's the purpose of "thrust balance" in Turbo Fan Engine? I'd like to know about the purpose of the Thrust balance system in commercial Turbo Fan Engine. Can you tell me the major role of thrust balance system? Also, the relations between thrust balance system and compressor / main bearing...
  35. B

    Acceleration Time if Thrust is Variable (polynomial)?

    Hi Everyone; I hope this is the right forum. Here's the issue... with fixed pitch propeller aircraft, thrust is not a constant, and changes (among other variables) with the speed the aircraft is travelling. The thrust available can be calculated using a polynomial. How do I integrate the...
  36. H

    Thrust for Car Acceleration: Understanding Piston Engine Force

    Can thrust be used to describe the force used to accelerate a typical car (piston engine)?
  37. J

    Soft drink bottle using compressed air for thrust to act like a rocket.

    Hey! This is the first time I have used this forum so I hope it all goes well and I am sorry if I break any rules on my first attempt. I have been given a question which I believe will involve quite a lot of work, so I thought I would get some suggestions as to where I need to start...
  38. M

    Calculating Jet Engine Thrust and Power | Rocket Thrust Question

    Homework Statement A jet aircraft is traveling at 246 m/s in horizontal flight. The engine takes in air at a rate of 77.0 kg/s and burns fuel at a rate of 4.00 kg/s. If the exhaust gases are ejected at 633 m/s relative to the aircraft, find the thrust of the jet engine and the delivered power...
  39. C

    Rocket Car: Constant Force Despite Acceleration

    recently i came across quesiton: a rocket car movves on str horz track. half of car mass is propellent, during run, propellent consumed at constant rate and ejected at constant nozzle velocity the answer says that force is constant but accel is increasing however i got a major question: by...
  40. S

    Can a Compressor Alone Generate Thrust in a Modified Jet Engine?

    What if someone took a jet engine and took out the combustion and turbine mechanism. Then that person found an outside source to power the compression mechanism. Can the compression mechanism alone produce significant thrust? That is, with an outside power that does not add heat into the system...
  41. J

    Finding Thrust from aircraft, need rolling friction

    Homework Statement An Airbus A320 jetliner has a takeoff mass of 75,000 kg. It reaches its takeoff speed of 82 m/s in 35s. Find the Thrust of the engines, don't worry about air resistance, but rolling friction is substantial. Homework Equations Fnet=mass*acceleration a=(82/35)...
  42. W

    Prop Thrust Qs: Find Answers to Static Thrust, Velocity Relation & TO Dist Calcs

    The following are a few questions that i have come across while writing takeoff distance code: 1. Assuming a known static thrust, how will this thrust vary as the airspeed increases? ex. Is the relationship linear? quadratic? how can i determine the coefficients of the "thrust in terms of...
  43. D

    A question about thrust VS mass

    I've always wondered about something. If there is no gravity or resistance in space, than why does it take more thrust to move a 1 ton object than a 1 pound object. Shouldn't thy both both be equally easy to move since neither has any weight in space?
  44. M

    Rocket Engine Thrust Formula Help

    hello, does anyone know how to derive the ROCKET ENGINE THRUST formula: T = P/R AV + (P-B)A i know you need to use F=ma and Momentum flow rate equations to get the first place. but what do you do after that? Any help would be greatly appreciated. Thanks, Michael
  45. Z

    Why is this wrong THRUST? i showed work

    why is this wrong...THRUST?? i showed work! Homework Statement A rocket for use in deep space is to have the capability of boosting a total load (payload plus the rocket frame and engine) of 2.25 metric tons to a speed of 10 000 m/s. If a different fuel and engine design could give an...
  46. K

    KrisDucted Fan Thrust: Understanding Jet and RC Engines

    :confused:Hi all, I’m new here; my name is Kris aged 53 in Norfolk, UK. I’ve been in engineering design all my life so they few theories and ideas I may submit for comment do have some sound basis. Anyway, today lesson (for you to teach me) concerns Jet Thrust and ducted fan motors. I...
  47. K

    Compare Net Work Done During Plane Dive & Climb

    A plane is diving toward the ground and then climbs back upwards as shown below. A lift force acts perpendicular to the plane's displacement, s = 1.7 x 10^{3} m, which should be taken to be the same for each case. The engines of the plane exert a thrust as shown which has the same magnitude...
  48. V

    GE90-115B Turbofan Engine: Thrust Analysis

    Hi, i am trying to increase the jet engine thrust. today most of the aircrafts are using high bypass ratio turbofan engine. thurbofan engine delivers thrust in two steps one: hot exhuast gas second : by pass air how i have to find the thrust developed by the bypass air? how i have to...
  49. S

    Rocket Thrust From a Spring (Work)

    Homework Statement A 11.7 kg weather rocket generates a thrust of 240 N. The rocket, pointing upward, is clamped to the top of a vertical spring. The bottom of the spring, whose spring constant is 560 N/m, is anchored to the ground. (a) Initially, before the engine is ignited, the rocket...
  50. M

    Formula for calculating turbo jet thrust?

    Can anyone tell me some formulae that i can use for finding the thrust in a remote control turbojet engine if the area of the intake is 196.35cm square and the exhaust is 78.5cm square and the pressure increases by 31 times?
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