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. F

    I Relativistic speed of a rocket with constant thrust

    I try to calculate the speed curve of a relativistic rocket driven by a 100% efficient engine with constant thrust, when traveling to a distant star. All equations I can find consider constant acceleration, which of course is not working, since the ships mass decreases when the fuel is used...
  2. K

    Thrust required for a Car driven by a propeller

    Out of curiosity, If suppose a car is driven/propelled by Propeller, how much thrust would be required to get it rolling or moving, then drive at 30 MPH, at 60 MPH and at 100 MPH? Consider the car weighs 6000 lb including passengers. If same car is inclined at 30 degrees, how much thrust is...
  3. 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...
  4. FreeBob

    What is the Career of a Retired Chief Technologist in Servo/Mech R&D?

    BSME Missouri University of Science and Technology (was University of MO at Rolla) '78 Retired after 32 year career in disk drives Chief Technologist managed about 150 electrical, mechanical and computer science engineers developing servo mechanics for hard disk drives Two boys, one graduating...
  5. 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.
  6. M

    I on my rocket engine thrust equation

    I have been working on a rocket engine and I have cad models and everything and I am getting ready to build it. Then, I was running over the numbers one more time and I realized that the thrust I was getting was completely different from what I should have been getting. The big problem is the...
  7. R

    Rocket thrust force calculation

    Homework Statement A rocket has weight 10,000 kg and it needs to carry 5000 kg with acceleration 3.5 m/s². How much thrust force is necessary for the rocket to have a flight from Earth to space? Homework Equations F=ma[/B]The Attempt at a Solution I try that, According to Newton's law, (...
  8. R

    Equilibrium Question -- Thrust versus Lift....

    Homework Statement Given: Thrust: 103000 N Lift = ? Weight = 86500 N Resistance = ? Homework Equations I'm just to figure out the value of resistance and lift. The Attempt at a Solution I can't seem to figure out a way to find out resistance, but with lift I believe it has something to do...
  9. A

    Thrust Bearings and Smooth Journal Bearings reaction moment?

    Ok, so this is an undergraduate level question probably but consider this R. C. Hibbeler's Textbook on Mechanics of Materials says this about thrust bearings and smooth journal Bearings : In other words, it says nothing about reaction moments. Now this chart has other 2D connection types...
  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. P

    Relating propeller thrust, power, and rpm together

    Hi All, I am involved in a research project regarding electric aircraft. I've done a fair bit of research into this but am having trouble keeping all the different parameters and how they affect each other straight in my head. Fundamentally I am putting together a model whose parameters I can...
  12. C

    I Rocket equation: is there an optimal thrust?

    This is my first post. I looked through many threads and could not find an answer to the question below. Well known equations in rocketry are: Delta Velocity = Ejection Velocity * ln (Final Mass / Initial Mass ) and Net Thrust = Mass Ejection Rate * Ejection Velocity – Current Mass *...
  13. Martin Skkinner

    What is Tapered land thrust bearing?

    I came across the word Tapered land Thrust bearing while reading about Babbitt bearing manufacturing. Can anyone help me with a layman's definition? How is it different from tilting pad?
  14. 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...
  15. M

    80,000,000 Pound Thrust Rocket

    I ran into the Sea Dragon Rocket that was cooked up on paper in 1962, could this have worked efficiently and if so could it have made it to where we would have been much further along in manned space and the ability to launch over sized payloads... Thanks...
  16. S

    "Net Forward Thrust": What does it mean in this problem?

    Homework Statement An airplane of mass 1.2 x 10^4 kg tows a glider of mass 0.6 x 10^4 kg. The airplane propellers provide a net forward thrust of 5.4 x 10^4 N. What is the glider’s acceleration? Homework Equations I The Attempt at a Solution Let T = tension on glider from airplane. M= mass of...
  17. GurfX

    Can space lasers power aircraft with unlimited range?

    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...
  18. 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...
  19. P

    What is the exhaust pipe diameter required for the given exhaust speed?

    Homework Statement The problem: Here is an approximate reaction for burning hydrocarbons in air: (CH2)n + 1.5*n O2 + 6n N2 -> n CO2 + n H2O + 6n N2 (n is an integer) The (CH2)n approximates the fuel, and everything on the right is the exhaust. The atomic masses of hydrogen, carbon, nitrogen...
  20. H

    B Propeller thrust in restricted air flow environment

    looking at where to start understanding how the thrust/lift generated by a specific propeller (hypothetical one) changes as a function of surrounding air pressure. obviously the lift will go to zero as air pressure decreases. as pressure increases, modeled by say mounting the propeller inside...
  21. W

    Calculating Axial Thrust for a Wheelchair Axle

    I'm in the process of calculating my combined stress on an axle I am designing, I have calculated the bending and torsional stress, however I need to calculate the direct stress in the axle. In order to do this I need to know the axial thrust in my axle, I understand what axial force is but I am...
  22. Xilus

    I Can Angular Momentum Create Forward Movement?

    OK so a trust can produce a torque, But two torques can't produce a thrust? There is no way to convert angular momentum into forward momentum.
  23. J

    Rocket Engine: Centripetal Force to Vector thrust

    Hey guys, I'm new to the forum and I have a question that has stumped several of the professors at my school. My idea is to use an electric motor with a solid rocket engine on a thrust stand to spin the exit cone. The concept would make use of centripetal force to increase the pressure of...
  24. P

    B How can a glider or an airplane do a loop without thrust

    I have to admit I am not good on physics but I am willing to try to understand how is possible for a plane or a glide that's falling without thrust applied downward to make a loop (by changing direction or using the elevators on the tail of plane, like in this picture. I am try to write a...
  25. Daquicker

    Minimal altitude to start a “Suicide Burn” - variable thrust

    Homework Statement I'm trying to calculate the absolute lowest safe altitude above a planet's surface to start firing the thrusters on a simulated lander in order tot just reach vCraft = 0 at the planet's surface. The force the craft's thrusters responsible for desceleration generate is...
  26. 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...
  27. C

    About interference, momentum and thrust....

    [Mentors' note - this post has been edited to remove some discussion of the EM-drive. See https://www.physicsforums.com/threads/nasas-em-drive.884753/ for our current policy with regard to em-drive discussions] Hello. Imagine a closed box with reflecting walls. Inside you have two antennas...
  28. Hercuflea

    Sailboat Speed Question: Can a Motor Increase Speed Beyond 10 Knots with Sails?

    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...
  29. tomwilliam2

    A Integration of velocity and thrust angle equation

    This is from a physics textbook, a chapter on rocket launch velocities, but really the question is how to integrate the first equation to get to the next. The way I was approaching it was like this: From ## V \frac{d\gamma}{dt}=-g \cos \gamma## Integrating from ##t=0## to some ##t##...
  30. BigREDgrin

    How do I Calculate Average Thrust when given t, v, delta m

    Homework Statement During a .0050 second time period a rocket expels 1.000kg of gas at a velocity of 5000 m/s. Calculate the rockets average Thrust, as well as Impulse. http://imgur.com/a/uE9dVI am going to use this note for reference on a test and want to rock solid about it. 2. Homework...
  31. 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. http://imgur.com/6liZSid Sorry image post no working, url: http://imgur.com/a/6XLwL We have to approximate the equation to a straight line through the curve...
  32. 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...
  33. N

    B Calculate Speed over Time: Net Thrust of 5.25 m/s & 124 Secs

    This should be a painfully simple question, and yet, I can't find the answer. once you have calculated the net acceleration force of an object, how do you figure out how fast it will be going over X seconds? example (taken from here...
  34. M

    B Leaf Blower Thrust for Bike: 450 cfm @120 mph

    Hi I want to make a leaf blower powered bike, And I need to know how much pounds of thrust Would I get from one leaf blower that puts out 450 cfm at 120 mph? Please help me solve this problem (Your help will be highly appreciated)
  35. cosmonium

    I Can Heat Differential Generate Thrust?

    This is an experiment I have wanted to do for a few years now but don't have the necessary equipment. GR tells us if you have identical objects with the same weight exactly when they are at the same temperature, then when one object is heated, it will weigh more. This is because the...
  36. Marco97

    I Marine Propeller Thrust: How Do I Calculate It?

    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...
  37. 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...
  38. F

    What Determines the Thrust of a Lorry Starting from Rest?

    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]
  39. S

    Thrust in a Water rocket (or any rocket?)

    I was debating with a friend, who insisted that the thrust in a rocket is merely due to the fact that a force PxA would have acted on a plate that sealed the nozzle. This force would have exactly balanced its counterpart "disk" on the other side of the chamber. After removing the seal, we are...
  40. A

    Thrust angle calculation for off-centerline airplane engine

    This isn't for any particular project or assignment, but I've tried solving this in the past and haven't figured it out. Say you have an RC seaplane, like the one pictured, with the engine mounted well above and aft the CG. You're going to need to angle it down a little to counteract the...
  41. A

    Propeller Weight & Number of Blades: Effects on 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...
  42. P

    Lift vs Thrust Force: How Is More Lift Than Thrust Possible?

    The thrust of an airplane changes the speed of the airplane, or you can look at it as it is increasing the airspeed relative to the airplane. The airspeed across the wings is only as much as the thrust allows it to be. The airspeed across the wing is what produces thrust, and I realize how it...
  43. J

    A 300 kg rocket sits on a launch pad. What is the thrust nee

    Homework Statement A 300 kg rocket sits on a launch pad. What is the thrust needed to obtain a thrust to weight ratio 3:1? Homework Equations The Attempt at a Solution 300.0 kg x 9.817 m/s2 = 2945.1 N i know this is not the correct answer, but i have no idea where to start. can someone...
  44. C

    Rotor blade thrust - torque and angular velocity

    Imagine a motor, spinning a rotor blade around and around and around and around and around... How does the angular velocity of the rotor blade, and the torque affect the thrust produced?
  45. 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...
  46. B

    Can't figure out solution -- Space probe with engine thrust vectors

    Homework Statement A space probe has two engines. Each generates the same amount of force when fired, and the directions of these forces can be independently adjusted. When the engines are fired simultaneously and each applies its force in the same direction, the probe, starting from rest...
  47. jdawg

    Find the thrust from the engine

    Homework Statement A static thrust stand is to be designed for testing a jet engine. The inlet conditions for the test are an inlet area of 1 {m2}, inlet velocity of 250 {m/s}, and gage static pressure of -22.5 {kPa}. The expected conditions at the 0.3 {m2} outlet are an exhaust gas velocity of...
  48. T

    MHB Starting with center of thrust to find amount of force on each point?

    I'm playing a game, From the Depths, that let's you build your own helicopter blades (and put them on ships that you build) and program in LUA. I did some searching and found: Calculating the Center of Thrust on Multirotors | Flite Test Currently, there is no way to tell how much lift a given...
  49. 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...
  50. 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!
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