What is Thrust: Definition and 343 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. Find thrust from water jet

Water jet comes from nozzle A=1m2, water speed is v=20m/s, density of water 1000km/m3, calculate thrust Is it possible to find thrust from this data? T=mass flow x v ? = 20m/s x 1m2 x1000kg/m3 x 20m/s= 400 000N ? Is more effective to use bigger nozzle A and slower water speed then use small...
2. Why is the thrust equation same under gravitational force?

The homework statement isn't exactly as is mentioned above. The actual problem statement is as follows: This is problem 3.8 from John R. Taylor's Classical Mechanics; however, my question is not related to the main problem itself but one particular aspect of it. Now, in the same textbook (John...
3. Rocket thrust equation in under-expanded nozzle

Hello, so the thrust equation goes like: F = (m dot)*v_e + A_e*(p_e - p_a), where F ... thrust [N] m dot ... mass flow rate [kg/s] v_e ... velocity of exhaust [m/s] A_e ... area of the exit nozzle plane [m2] p_e ... pressure of the exhaust at the exit of the nozzle [Pa(a)] p_a ... ambient...
4. Can the thrust of Ion Thruster be increased at the cost of speed?

Based on the little I know ion thrusters seem extremely impractical on earth, even because speeds over 20,000-30,000+km/h will result in immense friction and fire, so why not cut the high speed somehow and increase thrust which is abysmall? For example: the ions passing through a medium?? Wider...
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I Does Pulse and Glide only work with manual transmissions and a kill switch?

When car drive uphill, gravity/weight has drag component, that is reason why you must add more throttle compare to ligther car at same constant speed uphill. So logicaly car increase fuel consumption. But if you drive downhill, gravity/weight has thrust component, so your top speed("terminal...
6. 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...
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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...
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B Why does a stiff boat rudder produce forward thrust when pumped left to right?

In small sailing boat like optimist is well know technique when there is no wind, rudder pumping which push boat forward.You just need push-pull rudder left to right with fast movement. 1) Rudder is stiff(not flexibile like flippers for diving),so why rudder produce forward thrust if high and...
9. Bi-propellant Liquid Fuel Engine Pressures Before Thrust Chamber

Been reading Rocket Propulsion Elements 9th Edition and got approval from my university to design a bi-propellant liquid fuel rocket engine for my senior design project, and I've been understanding everything so far but I haven't quite found an answer to how the pressure works throughout the...
10. Help with thrust and HP needed to hover 300 pounds at 30' off the ground

If i wnat to lift/hover my self up 30ft off the groud (i am 110 pounds) how much HP would i need and how much would i need to lift/hover 300 pounds. Please answer TYSM
11. I Understanding the thrust generated by a typical jet engine

I was reading propulsion chapter 9 of Anderson's Flight book (http://213.230.96.51:8090/files/ebooks/Muhandislik/Anderson J.D. Introduction to flight (8ed., MGH, 2016)(ISBN 9780078027673)(O)(929s) EAs .pdf) and came to Figure 9.18 b) & c), Figure 9.19 (I cannot post the image here due to...
12. I Is the classical ideal rocket thrust equation correct?

Hello! I have recently found this fascinating article: https://zenodo.org/record/3596173#.YJ1ttV0o99B The author claims that classical equation for rocket thrust in incorrect because F is not equal to ma for a changing mass. Neither my professors nor me can see any errors. Do you think this...
13. Engineering Contact mechanics - Thrust bearing

Hello, I am doing some contact mechanics and I had an example in my Lecture notes about a simple thrust bearing with three balls where the bottom plate is stationary, the top plate rotates with angular velocity w, and the cage rotates with angular speed Ω. It says by inspection Ω =w/2 but I...
14. I Apollo 11: Torque & Thrust of LM RCS Systems

I'm writing a simulation software for the Apollo 11 missions, I'm not allowed to mention my website because of forum rules but you can see it in my profile. I am trying to now implement the RCS systems into the LM. The LM is the lander such as the one called "The Eagle" in Apollo 11. What I...
15. EDF Rocket with Thrust Tube: Physics Explained

Hi everyone. I am tasked with making an EDF rocket for a university project. The end of the rocket has a set of flaps that redirect air to control the rockets trajectory, seen in the image. The 90mm EDF itself is located near region 1.. I would like to know why, the physics behind it, a smaller...
16. Help With Understanding Thrust Calculations (rifle muzzle brake)

Let me start off by saying I decided to post this in the aerospace engineering thread because it directly deals with thrust, even though it is not for a plane or similar. I have two equations that I can use to calculate the force on a baffle of a muzzle brake, Equation 1, from The Engineering...
17. Thrust of Jet Plane: Why Is -313m/s^2 Wrong?

What is wrong with saying that since the speed of fuel goes from 0 to -313m/s (rel to ground) in 1s, then its acceleration is -313m/s^2. This leads to wrong answer according to author's solution but I don't see why.
18. Thrust Ball bearing and Needle Bearing

Hello all friends, My questions about the these two types of bearings. I know that what is purpose of usage. But I don't know where can I use them. If someone knows information about that, please inform me. Thanks you all.
19. I Orbital maneuver by applying a thrust in the radial direction

The author of my textbook writes that a spacecraft 's "thrust in the radial direction at perigee changes the energy but not the angular momentum". Such a thrust increases the eccentricity of the elliptical orbit of the spacecraft because ##\epsilon \equiv \sqrt{1+2EL^2/\mu C^2}##, where...
20. Ship thrust required to move out of the plane of our solar system

Hello, We know that most celestial objects in our solar system are in the equatorial plane of the sun. So too, does most of our spacecraft orbit in this plane as it explores our solar system. For a spacecraft already traveling away from the sun and towards the outer solar system, how hard...
21. B Thrust vs Gravity: What's Missing?

This is a conceptual problem. Consider two identical rocket ships in a gravitational field with no atmosphere. Ship A is hovering at a fixed altitude, ship B is ascending at a constant vertical velocity. Since neither ship is accelerating vertically, the thrust required of both should be the...
22. Understanding High Thrust of Vacuum Rocket Engines

Why do vacuum rocket engine always producing high thrust than sea level rocket engine ? for example spacex's merlin vacuum engine produce more thrust than merlin sea level engine. And it is due to the big nozzle with large area in vacuum engine because when the flow reaches mach 1 in the throat...
23. Momentum Thrust of an Over-Expanded Rocket Nozzle

Hi All, I'm trying to get a better understanding of the momentum thrust given by an over-expanded rocket nozzle (I realize this case voids the isentropic flow assumption used for the 1D isentropic gas expansion equations typically used for rocket engine design since the normal shock is not an...
24. Doubt related to buoyant force and fluid thrust force

(this problem is slightly modified from the original problem.) There is a contact force(friction and normal force) between the wedge and the walls of the container and there is a fluid thrust acting on the side of the wedge in contact with the fluid( this force is normal to the slanted surface...
25. How do ramjets produce thrust?

against what pressure produce thrust in ramjet if it is just hollow tube?
26. A jet engine's shaft is neutral in the direction of thrust?

I think i read somewhere that jet engine shaft is neutral,because forces at turbine and compressor cancle out,so that mean axial berings don't have force on it in direction of thrust!? (this can't be true,becsue in that case thrust will be zero...) But if this is true ,against what pressure...
27. Propeller thrust with backwards air flow

The Blackbird wind powered car travels directly downwind faster than the wind speed powering it. Typically a 10 mph wind from directly behind it will cause it to travel at about 30mph. I am trying to analyse how the car accelerates from rest. I know how it travels faster than the wind speed so...
28. Complex motion equation (projectile with changing mass and thrust)

I need an equation to predict the flight path of a changing mass projectile under changing thrust. Any thoughts?
29. Solving the Mechanics Puzzle of Meshcherskii: Understanding Thrust and Drag

"Collection of Problems of Mechanics" by Meshcherskii.I see how the answer could be arrived at because each successive drag increases the number of ropes that must be used, but what I don't understand is why the thrust and drag of the tug doesn't play a role in the number of ropes required.
30. Effect of thrust force on torque?

If I have a motor that is turning a shaft with only a small torque required but the shaft is also being forced into the motor, axially at a large force, what is the effect on the motor here? If Faxial is large, does this effect T and how does this effect the motor?
31. Prop disc thrust uniformity in turns vs wing position

I would like to know what is the current consensus on the effect of the position of the wing relative to a tractive propeller disc's uniformity of thrust (the focus configuration would be WWII fighters).
32. Personal Jet Boat Water Craft Thrust Question

Assume a jet boat or personal water craft (JetSki, etc) has a movable propulsion nozzle. This nozzle can be moved vertically so that the water jet driving the boat forward can be either above the surface or below the surface of the water. Further clarification. You are speeding along on your...
33. Calculating the normal force due to moment load on a thrust bearing

Hello all! I have a mathematical question for you. I'm trying to design a thrust bearing that can withstand axial and moment loads. I've added a picture of a similar design. The design consists of two rings (grey) and sliding pads (blue) fixed on the bottom ring. The top ring slides over the...
34. Underwater thrust formula?

I'm trying to determine the force needed for one object to displace another object underwater. Specifically, Object A strikes Object B hard enough to jettison it from the seafloor up to sea level/land, let's say the Pacific coastline. I have a timeframe in mind, density & mass of the two...
35. 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...

37. Do surfaces ahead of propellers decrease thrust?

Hi! I have had this question for ages, nearly impossible to find anything on the web. My experiments confused me even further! Its concerning the blockage effects of surfaces ahead of a propeller. For example let's consider the usual dual vectoring propellers on the sides of airshipcars like...
38. Thrust of a large ship's propeller accelerating the ship

Hello. Not sure how to even begin with this question honestly. Didn't learn anything about thrust regarding this topic so it got me dumbfounded. Here's how I try to interpret it: I'm assuming that the thrust created by propellers = net force of the ship, where I can use F=ma to find...
39. Does thrust get cancelled by a rotating crank?

I have a frame which supports a crank rotating through 360°. The crank lifts a 30 kg weight 540 times a minute ( 540 rpm). As the crank moves 0° to 90° the weight is accelerated to full speed which means it has thrust but then from 90° to 180° it is slowed to a stop then from 180° to 270° it is...
40. Thrust on an triagular lamina emersed in a liquid.

I feel there is a really obvious flaw in my logic but i can't pin it down So i have to find the thrust on the lamina which is basically force of bauyancy F(bouyancy)= Vρg Now volume of the triangular lamina is its rea into its hieght. v = Ah hence F = Ahρgsome information i feel i didnt take...
41. Thrust 6.05MN, mass 4,520,000 lbm, what is the acceleration?

if the first stage provides a thrust of 6.05 mega-Newtons [MN] and the space shuttle has a mass of 4,520,000 pound-mass [lb Subscript m], what is the acceleration of the spacecraft in miles per hour squared [mi divided by h squared]? Equation: F=ma conversions: 1000m=0.621mi 3600s=1 hour I'm...
42. Hydrostatics Pressure - Finding thrust and resultants

Homework Statement I'm getting stuck with this one and in need of some direction! Obviously I'm not looking for a direct solution, but maybe a outline of what I should be doing? (I'll attach an image in a few minutes) <Image here incoming!> Known data: d2 = d1 / 2 F = thrust force (N) Pa = ρ...
43. Calculate the resultant thrust and overturning moment

Homework Statement A vertical retaining gate 2metres X 24metres hinged about the bottom edge of a dry dock has water to a depth of 21 metres on one side. Calculate the Retaining Force at the middle of the free upper edge of the gate to keep it shut in the vertical position. With the density of...
44. How can we determine the thrust generated?

Homework Statement How can we determine the thrust/ propulsive force generated? We know that: There is C02 inside a given Volume V and we know the mass M of the gas inside the volume. We know that we release the gas from a hole of diameter 1.6 mm. Homework Equations PV=nRT ∑F= dp/dt ∫u(t)...
45. 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!
46. I Rocket-Jet Hybrid, Rocket + Ramjet

I read that a thrust augmentor can significantly increase the efficiency of a jet engine (http://www.pulse-jets.com/phpbb3/viewtopic.php?t=931). 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...
47. 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...
48. 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...
49. Thrust and Centre of Pressure

[Moderator's note: This thread was created by moving posts from another thread, hence no homework template] The name "centre of pressure (COP)" indicates representative pressure will act through this point for a vertical plane inside liquid. If so, then total thrust= vertical area of the plane...
50. B Thrust Calculation: 1000 psi Tank, 1 in² Removed

Let's say we have a tank with 1000 psi pushing in all directions, if we remove one square inch from an end, now the tank has 1000 psi more at one end than the other. Does this mean that there is a 1000 lb push in the opposite direction of the removed square inch?