Thrust Definition and 40 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. gggnano

    What's wrong with this math: A lot of thrust and almost no fuel?

    So according to this if you need a force that can lift a human and even an extremely ultra-light craft (1500 N) and have a velocity of 200 m/s you can eject extremely small amount of fuel through the nozzle: 0.0007 or less kg per second for as long as you're using 15 MPa pressure which is doable...
  2. D

    Sci-fi engine thrust calculations

    Hi all, I'm writing a technical manual for a starship in a science-fiction series I'm working on, I wanted to check with some folks here to make sure my calculations are correct concerning the ship's engine thrust. The ship has a fully-loaded mass of 5 million metric tons. Using its...
  3. B

    Function for the Thrust of a Ducted Fan

    I'd like to design a ducted fan capable of generating 800 N of thrust. Though I can do fairly high level math, I just really don't even know where to start in calculating (or at least relatively accurately estimating the thrust generated by a propeller, particularly a ducted one (as I understand...
  4. AdrianHudson

    I What is the difference between thrust and thrust density?

    The picture above has thrust density as a column and I am not too sure what that is. Can anyone explain to me what the difference between thrust and thrust density? Thank you for your answers!
  5. Julian Erickson

    I Rocket-Jet Hybrid, Rocket + Ramjet

    I read that a thrust augmentor can significantly increase the efficiency of a jet engine ( Now from my understanding, the thrust agumentor is sort of like a ramjet. Only, in this case, the cold air is being sucked in along with the hot air...
  6. ckirmser

    Could a <1g acceleration vehicle escape Earth's gravity well

    Hello, all - A question has come back to tickle my brain. Could a vehicle with less than 1G of thrust manage to escape the Earth's gravity well? I'm thinking something like Space X's Falcon 9. As it landed, with just a little more thrust, it could go back up again, I would guess. So, if it...
  7. Arjun Singh

    KiloNewton/Pound foot of thrust into Horsepower units

    Hi, I am currently studying aviation engine outputs and to make my study linear in comparative analysis with standard Automotive engines I need some expert help. Can anyone help me drive precise equations to convert: 1. Engine thrust in Kilo Newton into Horse Power and Watts 2. Engine thrust in...
  8. FreeBob

    Calculating equivalent horsepower for a jet engine

    Trying to remember some basics. I know the thrust of a jet engine. I'm thinking about equivalent HP. I can establish HP at a given speed, but what about while accelerating? I will display my ignorance here :( Power for static, non accelerating flight: Power = [Thrust x Airspeed] Thrust...
  9. P

    I Is it possible to use the vacuum to launch a rocket?

    Hey I'm new to Physics. I have a question. Is it possible to use the force generated when air entera a vacuum tube to launch something into space? Can anybody throw some light on this in simple words please. Thank You.
  10. PhysicsKid0123

    Center of mass, Newton's third law, and rocket thrust

    Can someone clarify this for me-- how is the motion of the center of mass unaffected by internal forces, as is stated towards the end of the paragraph in the picture I've provided. It seems to me that motion of the center of mass directly affected by these internal forces. Specifically, the...
  11. L

    Force produced by flow in aircraft engine

    Homework Statement Consider an aircraft turbine as in the figure below. In the reference frame of the turbine, air of density ##\rho_0## comes into the turbine with speed ##U_0## through the entrance with cross sectional area ##S_0##. In the combustion zone, air is mixed with the fuel and...
  12. GurfX

    Extreme heat/plasma thruster

    My knowledge suggests when gasses are heated rapidly, they also expand due to the new energy in the gas. Is it possible to create a thruster that is able to lift 10kg via electric heating? The thruster would allow cold air to enter the chamber, where it would then be super-heated & ejected as...
  13. A

    Could you create thrust with water vapor?

    Whilst I was thinking of hydrogen combustion jet engines. I thought of a little idea... What if you could create thrust with water vapor the same way you could with the exhaust gas of a jet engine. (NOTE: I have no experience in engineering and I only have a mild interest in it). If this is...
  14. R

    Aircraft Propeller Blast velocity while in motion

    I am working on a range extender for full size electric aircraft. It is a turbine located under the cowling, protruding only 8 inches. On my full size static model, the turbine can produce 600 watts with the prop blast v measuring 38 mph. If we could fly the plane (we can't, no wings) at 80...
  15. C

    About interference, momentum and thrust...

    [Mentors' note - this post has been edited to remove some discussion of the EM-drive. See for our current policy with regard to em-drive discussions] Hello. Imagine a closed box with reflecting walls. Inside you have two antennas...
  16. Hercuflea

    Sailboat speed question

    This is not a homework question, I'm just curious. Suppose you had a sailboat sailing on calm water. Let's say the sailboat is capable of sailing at 10 knots under the current wind conditions using only its sails. Now say the sailboat had a small propeller motor that was capable of propelling...
  17. B

    How to find force from volumetric flow rate and pressure

    1. Homework Statement Hi. This is a problem related to designing a RC hover craft. We are given a datasheet for a fan used as thrust. Sorry image post no working, url: We have to approximate the equation to a straight line through the curve...
  18. G

    Mass flow rate through a regulator

    Hi, We have a canister at a set pressure (4500psi) full of compressed air. A single stage pressure regulator is fitted to the canister that reduces the outlet pressure to 850psi. The flow from the regulator is then used in a divergent nozzle to create a thrust force capable of lifting a small...
  19. Marco97

    I Marine propeller thrust?

    Hello folks! I hope all of you are having a good day. Here is my question: How can I calculate the thrust needed by a marine propeller to move a body of about 120 kg? Also, as long we are talking about marine propeller, our propulsion is in water and not in air, so what about the rpm? Are they...
  20. J

    Speed of Hydrogen combustion out of a tube?

    Hello, I was curious about how to calculate how fast the escape velocity of hydrogen out of a tube/cylinder would be. Once end of the cylinder is closed, the other is open, obviously. Assume the cylinder is full of hydrogen at 1 atm. My thought is that you could use PV=NRT to calculate the...
  21. F

    How to calculate thrust

    Homework Statement The lorry starts from rest with an acceleration of 2 ms-2. What is the effective thrust is being exerted? Homework Equations acceleration=2 ms-2 starts from rest so initial velocity =0 ms-1 The Attempt at a Solution F=ma [/B]
  22. A

    Propeller and thrust

    Does the weight of a propeller have any effect on the thrust provided? For example, if there are are two propellers of the same size same speed but different weight, would the one with more weight have a greater or lesser thrust? also would effect do the number of blades(faces) have on the way a...
  23. C

    Nanoscale propulsion system that works in vacuum - or not?

    Moved this question from the quantum physics section to this section, since... Well it fits this section better since electrons apparently do obey conservation of momentum in the 'classical' sense. Why not produce thrust in microgravity with electrons? Plenty of harnessable electricity in...
  24. AEGIS

    High school project -- Finding mass flow rate, air velocity

    Hi, First-timer here! I'm designing a physics project that involves pumping a certain pressure of air into an empty bottle. SETUP: The bottom of the bottle has a small hole through which a thumb tack fits tightly; the top (cap-side) has a valve through which the air is inserted. The bottle is...
  25. R

    Thrust of an underpressure tank of air

    How can I calculate the thrust of an underpressure tank of air when the valve is released? If you can, please, explain in detail. Thank you!
  26. 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...
  27. S

    Need help with model rocket thrust

    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...
  28. 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...
  29. 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...
  30. 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...
  31. 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...
  32. M

    Propeller's Thrust

    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 about...
  33. 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...
  34. 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) +...
  35. 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...
  36. 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...
  37. 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...
  38. 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...
  39. 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...
  40. 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...