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. N

    Could one use magnets to create friction and thrust

    if I had a motor with a pendulum and a magnet at the end of it, and attached to this motor was a frame holding a another magnet that is close enough to the pendulum to exert force on it when it is horizontally positioned would that force make friction with the inside of the motor creating thrust...
  2. J

    Is thrust linearly related to propeller-pitch?

    Simple question, Given a constant speed, is the thrust of a propeller linearly related to it's pitch?
  3. B

    How Does Rain Affect the Momentum and Speed of a Moving Cart?

    Homework Statement An empty cart travels at 15 m/s as the rain begins to fall. The rain goes into the cart, and adds 10 kg of mass per second. 1) Will the rain cause the momentum of the cart to change? 2) Write an equation for the speed of the cart as a function of time. 3) How fast will this...
  4. evan-e-cent

    At what pressure does steam exiting a nozzle reach mach 1

    I am planning to build a Hero's steam engine or Aeolipile. This is the steam engine invented by the Greeks about 2000 years ago. It is attributed to Hero or Heron (10-70 AD) but was also referred to in 15 BC. My grandfather build one for a show. I have inherited it but rather than try to repair...
  5. ScramjetCCO

    Continuous thrust orbit changes

    Most threads about making orbit changes assume impulsive changes in velocity (short period bursts). What if one wants to increase the radius of a circular orbit with a very small constant thrust? I assume the thrust should be applied tangentially in the direction of travel, but what would be the...
  6. Gbl911

    Center of Lift vs. Center of Thrust

    I have been thinking about the CoL and CoT on rockets. I came to the conclusion that they are in the exact same spot on the rocket since your thrust and lift come from the same thing in the same place, the engine. I read some forums on other websites but didn't get a clear answer. It would be...
  7. S

    How Does Adding Mass Affect the Thrust of a Model Rocket?

    Homework Statement Hi. I'm in high school physics, and as I'm only 2 months in, I still don't know much. We launched a model rocket as an experiment and I need to find the thrust after adding 100g of mass to the rocket's body. The engine is an Estes A8-3. My teacher told me that its thrust is...
  8. P

    What Is the Required Thrust Force to Launch a 590 kg Rocket?

    Homework Statement A 590 kg rocket is at rest on the launch pad. What upward thrust force is needed to accelerate the rocket uniformly to an upward speed of 28 m/s in 3.3 s? Homework Equations V = Vi + at F = ma The Attempt at a Solution I'm just confused about what "thrust force" actually...
  9. R

    Find maximum thrust of a rocket blasting off

    Homework Statement A 2.49×104-kg rocket blasts off vertically from the Earth's surface with a constant acceleration. During the motion considered in the problem, assume thatg remains constant. Inside the rocket, a 14.5-N instrument hangs from a wire that can support a maximum tension of 37.3 N...
  10. Kushwoho44

    Fluid Dynamics: Static Thrust on a Conv-Div Nozzle

    Homework Statement The attempt at a solution Hi all, I am tasked with finding the static thrust generated by this convergent-divergent nozzle. The stagnation pressure is known the inlet. Now, personally, I would've thought drawn a control volume around the entire nozzle. And then said...
  11. T

    Compressed Air Reverse Thruster

    Hello everyone, I'm attempting to determine the impulse that can be generated by expelling compressed air from a pressure vessel stored aboard a moving craft through nozzles in the nose of the craft. The vessel has a forward momentum of roughly 2,000,000 Ns. EDIT: For semantics sake, consider...
  12. J

    Thrust imparted from a photon?

    If I produced a material that neither absorbed nor reflected light. Or at least did so to an extremely miniscule amount and set it in space and hit it with light. Would there be any thrust imparted unto it? If so would it be significant? My initial thoughts would be that sense it is massless...
  13. rickitek

    Questions about thrust in pressurized environment

    is the thrust equation F=MA applicable only in atmospheric condition? can we use this equation in vacuum or pressurized space, thanks!
  14. G

    Forces induced by a vehicle wheel on the ground

    Hi, I was wondering whether anyone can help with a question I have about the forces acting on a car wheel and the forces the wheel induces on the ground surface. The way I understand it, a car wheel traveling on a flat surface has the following forces acting on it: -vertical force due to the...
  15. C

    Who is pushing who in Newton's Third Law of Motion?

    I read this description of thrust on gcsescience.com; "Hot gases are forced downwards through the rocket's jets which pushes the body of the rocket upwards.This is an example of Newton's Third Law of Motion. " I've learned already that Newton's 3rd law states that for every action there is an...
  16. D

    How to calculate net Thrust of rocket

    Trying to calculate the net thrust of a rocket taking into account the force due to gravity. So I presume this is the calculated Thrust minus the force due to gravity. Known data so far is that the rocket gets to escape velocity (11,200 m/s) after 5 minutes (300 secs). Acceleration for this is...
  17. Pyrus

    Calculating Thrust on Curved Surface of Cylindrical Vessel

    Homework Statement A large cylindrical vessel contains water to a height of 10 m. It is found that the thrust acting on the curved surface is equal to that at the bottom. If atmospheric pressure can support a water column of 10 m, the radius of the vessel is:- (a) 10 m (b) 15m (c) 5 m (d) 25 m...
  18. ali nemati

    Maximum Thrust force in submarine

    I am designing a submarine in low scale that the max propeller OD is 10 cm, means from center of shaft to propeller edge I have around 5 cm distance. I am trying to find the maximum thrust as this submarine suppose to pull an object inside water pipe. I need to find optimum rpm ,blade number...
  19. R

    Axion thrust by enhanced scattering

    Axions in theory are uncharged, spin 0, very light particles, and have a very small scattering cross section when interacting with photons. But there is a very interesting article about a strong enhanced scattering of neutral particles. "Resonant radiation pressure on neutral particles in a...
  20. A

    Torque & Force required to slide a gate

    Greetings all, I am trying to build a sliding gate operator. I have this wiper motor which says, 24v dc, 64rpm, nominal torque- 4Nm. Max weight of gate to be 400kg, sliding on a steel rail (Not sure how to consider rolling resistance or Co-eff of friction) . Max pull force to be achieved by...
  21. Q

    What is a good power source for a personal flying machine?

    Hello, I am trying to build a personal (one-manned) propulsion system that will allow individuals to fly above the trees, preferably fast, and for long amounts of time. I plan to do so using propellers. The power will need to be plentiful and long lasting. These are some options that I am...
  22. M

    Calculating Propeller Thrust for Custom-Made Drone

    I would like to know how does the general equation about propellers thrust look like. How should I calculate the force to be big enough for a lift off? The object (a drone) is located in a spacecraft , which means the gravitational force is 0. Are there more variables that I should concern...
  23. D

    Human capacity for G-forces, Energy calculation, and thrust

    I hope this is the right place for this... Question #1. How much can the human body stand multiple rapid G-force changes. Like let's say I made a vehicle that you could make sure all your body parts were 100% secured and it could move freely in space in any direction what would be the result of...
  24. mootz

    Horsepower needed to lift 600 lb load, w/8 motors

    Good day Geniuses. im building a drone prototype for an agricultural project. approx. weight will be 600 lbs, using my own 8 rotor design. trying to determine rotor size and motor power required to fly such a device at 30 feet. would also be interested to determine an approximate wind speed...
  25. E

    Variable mass calculation of thrust for a water rocket

    Homework Statement I am trying to derive the formula for time varying thrust given that I know the initial mass/volume of water in a water rocket. Knowns will include initial pressure, initial volume of water, and nozzle cross sectional area. Homework Equations Bernoullis equation: (p/ρg) +...
  26. A

    Force of Friction on Boat w/ Thrust

    Homework Statement A boat moves across the water at a constant 30 mph towards the west. If the motor is generating a thrust of 500 M then the force of friction on the boat must be... a. 500 N to the east b. 500 N to the west c. less than 500 N to the east d. less than 500 N to the west...
  27. O

    Principle of linear momentum for a rocket

    Homework Statement vertical rocket start: F_thrust (simple F) Δm (fuel consumed per Δt) m_tot the relative velocity of the gas w is demanded. Homework Equations vgas=v+Δv+w, w<0 m(t)=mtot-Δm*t The Attempt at a Solution rocket acceleration. F-G=m(t)*a(t) a(t)=F/m(t)-g first...
  28. S

    Thrust in Newtons (aviation)

    Given that an engine's rated power is 160 HP (~119kW), how can I express thrust (T) in Newtons, if aerodynamic drag (D) requires weight expressed in Newtons as well to ensure consistency when calculating power available (Pa) and power required (Pr)?: D = (\frac{1}{2}\rho...
  29. pixartist

    Calculate thrust of a rocket in order to approach and keep a position is space ?

    Okay, first of all, I'm not very good at maths, so I will have to talk in programmer terms here. I have the following issue: A small rocket is moving in space, and I want it to move to and stay at a location in space, similar to a quadcopter. No as far as I see it, I have the following variables...
  30. B

    Help with compressed air thrust

    I'm working on a kinda-sorta confidential device. I would like to know how much psi is required to lift approx. 400 pounds 120m (about 393ft and 8 13/32 inches) into the air. The thing I'm working on is still in the designing stage, so don't worry about the specifics of individual thrusters and...
  31. A

    Blade Runner -- Prosthesis propulsion question

    Hi there. I have come to this forum to try and find someone able of helping me with some (im sure) basic Physics. I'm trying to work out the Physics behind the Prosthetic carbon fibre legs that Oscar Pistorius uses, a diagram would be incredible! I want to know what calculations would be...
  32. M

    Looking to fly. need speed. Have other dimensions

    Hey everyone, I have a theoretical problem. I have a box. Rounded off but not greatly aerodynamic. It is 800 kg including propulsion. I have wings with a max of 2.25m long and a max width of about 2m wide. This is the length of the box. I need to know how fast the box needs to go with those...
  33. kq6up

    Straightforward and Rigorous Rocket Thrust Derivation

    I have noticed many of the thrust derivations in textbooks I have seen do not do a straightforward derivation of rocket thrust. The all seem to use the same trick with infinitesimals in a sort of binomial form. For reference: Taylor, "Classical Mechanics" Pg. 85. I am working on a rigorous...
  34. R

    Thrust from model engine exhaust

    I’m interested in your views on whether any significant thrust could be obtained using the cooling air and exhaust gases from a model aircraft engine. International class control line speed models (known as F2A) achieve speeds of around 300 km/hr using 2.5cc engines and tuned pipe exhausts that...
  35. P

    A question about the thrust of light

    Hi everyone I am a layman at physics am would be very grateful if someone could assist me with a question about propulsion. The question arises from an article I recently saw discussing NASA's testing of a Cannae Drive...
  36. Q

    Calculating Speed of a Rocket Using Mass and Thrust

    Hi guys, I would like to count sth., but to do that i need a speed of thing. The promblem is that I've got mass ~150 gram (0,33 pound), enginee thrust 1700 gram (3,75 pound) which work 4 seconds (it moves up) and I don't know how to count this. Do you know, it is possible to count speed based on...
  37. Rookie

    Rocket Thrust, Acceleration, Velocity and Altitude

    Having some trouble with this problem. I'm not sure if the first part is correct, I just need some feedback on that. Also I'm not sure how to calculate velocity or altitude after 1 second. Any help would be awesome! Homework Statement A rocket has an initial mass of 4000kg, of which 3000kg is...
  38. G

    Inefficiency from redirected thrust?

    I am trying to figure out how much thrust would be lost in redirecting it. I understand that that harrier jets redirect their thrust downwards to generate upward thrust but surely they lose some efficiency due to turbulence and friction inside the redirection duct. My question is how much is...
  39. T

    Thrust produced by a steam rocket

    I'm trying to calculate the thrust produced by a steam rocket, but I don't have that much information to work with (or at least information I don't know what to do with). It's 2m long and has a diameter of 1m, and it's constantly filled with water at a rate of 170.344L/sec, which is...
  40. H

    Thrust (pitching and plunging)

    Hello, i am wondering a situation; how does the thrust occur in pitching and plunging motions? thank you for reply.
  41. C

    Validity of rocket pressure thrust term

    My first post, and a very long one... I have problems understanding the prolific use of a certain term in the rocket thrust equation and its validity. The general rocket thrust equation contains a term referred to as the pressure thrust. It is calculated as (p_e – p_a)Ae where p_e is the...
  42. C

    Thrust and acceleration of a launch vehicle

    Homework Statement Here is the data I have been given; mass = 3.4*10^6 kg (at lift off) mass of first stage propellants = 2.0*10^6 propellant consumption rate = 1.4*10^4 kg/s g = 9.8 m/s/s Find the thrust of the engines at lift-off. Homework Equations a = T-mg/m The Attempt at...
  43. N

    Calculating Thrust Needed for 200g Model Rocket Acceleration

    Homework Statement What thrust does a 200g model rocket need in order to have a vertical acceleration of 10.0m/s^2? A) on earth? B) on the moon, where g=1.62m/s^2 Homework Equations The Attempt at a Solution I am not sure of an equation to use for this problem
  44. X

    Calculating Exhausted Mass Velocity in Rocket Thrust Manipulation

    Hey everyone, so I'm just wondering if you guys can articulate the term "velocity of lost mass" from the rocket. After a few massaging on the equations(derivatives and integrals stuff) i found that to manipulate the thrust, one must manipulate the burn rate AND the "velocity of loss mass". all i...
  45. R

    How Do You Calculate Static Thrust from Fan Specifications?

    Hello, How is it possible to calculate the static thrust from a fan given power, radius, air density, and propellor efficiency? I've did some research and found various equations that all gave me varying results. Does anyone know what the real static thrust equation is? Thanks...
  46. R

    Calculating the thrust required to turn a submarine deep in the water

    Dear All, I am designing a AUV and trying putting a bow thruster in the front. I am kinda confused that how much power do I need to turn my AUV by a steady angular velocity. Could anyone pls help me with this. Regards
  47. E

    What is the Optimal Nozzle Exit Pressure for Maximum Thrust in a Turbojet?

    Hello, Im wondering if an analytical proof exists that shows why maximum thrust in an ideal turbojet is obtained when the nozzle exit pressure is expanded to the ambient pressure. As in the equation.. F = mdot*(Ue-Ua) + Ae*(Pe-Pa) my intuition tells me that we'll have to take a...
  48. H

    Calculate Thrust of Rocket: Homework Statement

    Homework Statement A rocket has an initial mass of m0 = 30,000 Kg, from which 80% is fuel. The fuel is being burned at a rate of R = 200 kg/s and the gas is expelled with a velocity of vrel = 1.8 km/s. The velocity of the rocket is calculated by: v = vrel* ln \frac{m0}{m0 - Rt} - gt...
  49. 3

    Power and Thrust of a Motor/Propeller

    I'm having some issues finding the relationship between power and thrust of a motor of a standard propeller based aeroplae. I've found two simple relationships that both make sense, but both (seem to) contradict each other. Thrust is equivelant to change in momentum: T = Mdot*v Power is...
  50. F

    Momentum in a space shuttle and thrust

    Homework Statement The space shuttle, with an initial mass M = 2.41 x 106kg, is launched from the surface of the Earth with an initial net acceleration a = 26.1 m/s^2 . The rate of fuel consumption is R = 6.90 x 103kg/s. The shuttle reaches outer space with a velocity v0= 4632m/s, and a mass...
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