What is Propulsion: Definition and 290 Discussions

Propulsion is the action or process of pushing or pulling to drive an object forward. The term is derived from two Latin words: pro, meaning before or forward; and pellere, meaning to drive.
A propulsion system consists of a source of mechanical power, and a propulsor (means of converting this power into propulsive force).
A technological system uses an engine or motor as the power source (commonly called a powerplant), and wheels and axles, propellers, or a propulsive nozzle to generate the force. Components such as clutches or gearboxes may be needed to connect the motor to axles, wheels, or propellers.
Biological propulsion systems use an animal's muscles as the power source, and limbs such as wings, fins or legs as the propulsors.
A technological/biological system may use human, or trained animal, muscular work to power a mechanical device.

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  1. mimi10

    How to become a propulsion engineer?

    As an entry level graduate, I'm exploring some ways to become a propulsion engineer. How can I become a propulsion engineer? What all should I consider to learn (both concept wise and software) ? What are other roles related to the path of a propulsion engineer that one must try?
  2. ksh93

    I Can a permeable but non-magnetic rotor be used in an electric motor?

    Let's say, the disc has a circumference of 1m, made of steel, or copper if you like. The stator has a north and a south pole facing the surface of the disc, let's say at the perimeter of the disc, one perpendicular to the left and one perpendicular to the right ie opposite sides of the spinning...
  3. Trikenstein

    I Swimming in space, it is a possible propulsion?

    Let's imagine a space tourism program where there is a fun part, the tourist can wander freely in space with a jetpack. Let's assume I stray randomly in space, floating leisurely in zero gravity. Then I detach my jetpack, just the time to make a selfie. While fiddling with the phone to setup...
  4. JoeDGreat

    What is the rocket's initial acceleration?

    Help me solve... I'm getting errors here..
  5. D

    Shifting from Mechanical Engineer to Aerospace Engineer

    Hello, Has anyone here started out as a mechanical engineer and shifted to an aerospace engineer? How necessary is an aerospace engineering degree to get into that field? What are some of the barriers that would exist for a mechanical engineer and how would you best get into that field? I am...
  6. klwong

    I Moving Spacecraft propellent less?

    Assuming there are four robot inside a stationary spacecraft (mass 2 ton) , robot A has an electric gun that can shoot iron balls weighing 1kg at a speed of 8m/s. These balls collide with red balls at a 45-degree angle in a two-dimensional elastic collision. Each ball has a mass of 1kg. The red...
  7. Erik1801

    Realistic fast Interstellar Propulsion Methods

    This is my first time posting, so please excuse any mistakes. I am grasping at straws here. I am working on a Hard-Sci Fi novel, plot, arcs, characters etc. are all worked out and i decided to take the deep dive in terms of Realism. For instance, there are no Fusion reactors. All that is...
  8. C

    NASA What is the propulsion method for the metallic orb?

    Here is a video of the metallic orb captured by a US drone. Wondering about the physics of how such an object could fly.
  9. Astronuc

    Nuclear Thermal Rocket (NTR) propulsion

    NASA, DARPA Will Test Nuclear Engine for Future Mars Missions - But then that's been stated periodically in the past. https://www.nasa.gov/press-release/nasa-darpa-will-test-nuclear-engine-for-future-mars-missions Obviously we won't be sending a manned mission to Mars by 2020 or 2024, and...
  10. D

    ESA's Dual Stage 4 Grid Ion propulsion

    I have found remarkably little information about ESA's Ion Drive in collaboration with Australia: https://en.wikipedia.org/wiki/Dual-Stage_4-Grid https://www.esa.int/gsp/ACT/doc/PRO/ACT-RPR-PRO-IAC2006-DS4G-C4.4.7.pdf Reference...
  11. S

    Exploring Propulsion with Light & Magnetic Fields

    while browsing for new propulsion methods I found the following interesting: https://en.wikipedia.org/wiki/Radiation_pressure "Radiation pressure (also known as light pressure) is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the...
  12. Austin_Tx_Rockets

    Does the discharge coefficient of an injector depend on the fluid?

    The discharge coefficient is the ratio of the actual discharge to the ideal discharge and can be measured experimentally. If one were to experimentally measure the discharge coefficient using water, would this value be constant for all incompressible fluids? What does the discharge coefficient...
  13. Abheer Parashar

    Rotating Detonation Engine, the future of aviation propulsion?

    Hello everyone, I am Abheer and I am a high school student. Few days back I saw an article about RDEs (Rotating Detonation Engines). The article said it is the future of aviation propulsion. I want to ask, is it really so that RDEs are future or the low/high bypass turbofan engines will continue...
  14. Astronuc

    The Future of Rocket Propulsion, What To Do About Emissions

  15. J

    B How is efficiency defined in rocket propulsion?

    Whicle has 4 wheels, inside is oval closed room with fan that blow inside air to the wing. Wing produce difference in static pressure in direction of travel. Will vehicle move forward or not? If I look just at pressure difference at wing, vehicle will move forward but I know from Newton 3 law...
  16. J

    I love Octonions as well as alternative propulsion ideas

    How did you find PF?: Google Hi folks! Title sums it up pretty well. Alternative propulsion is cool, despite the amount of woo that tends to permeate the topic. I enjoy finding first-principles solutions for far-out claims.
  17. V

    Trouble with a Rocket Propulsion question (Variable Mass & Momentum)

    I chose to set the upwards direction to be positive and dM/dt = R = 190 kg/s, so I can solve the problem in variable form and plug in. With the only external force being gravity, this gives M(t) * dv/dt = -M(t) * g + v_rel * R where M(t) is the remaining mass of the rocket. Rearranging this...
  18. E

    New type of rocket propulsion design, and why it might not work?

    Hi, *Excuse the crude visualization and possibly imprecise description - I'm not a rocket scientist :) So, I have a friend that has come up with a "new" concept for a rocket propulsion design, and although I have a hunch that it might not work better than existing designs I cannot really...
  19. L

    B Space propulsion without mass ejecting

    When the pulse is given at A, the box move to the right. When it is absorbed at B, the box stop.
  20. D

    Laser Propulsion in space -- please see the attached diagram....

    Please help me understand why this is a concept that has not been studied? The laser sail is really the only info I can find in this area using a laser from a fixed source. Using liquid nitrogen to cool the mirrors and reflecting lasers off of them for propulsion. I'm a Doctor of Pharmaceutical...
  21. Limebat

    Need help on model HHO propulsion systems

    Hey all, Lime here. I've been getting into HHO for a while, and I think I almost have my DIY generator up and running (waiting on eBay 18650 batteries). I was thinking a fun little project is to play around with a few concepts with my new found combustion source. Anybody here know a good way to...
  22. yucheng

    Rocket propulsion equation: what's the error here?

    Equation for rocket motion: $$\frac{d \mathbf{P}}{d t} = M\frac{d \mathbf{v}}{d t} - \mathbf{u}\frac{d M}{d t}$$ But $$\mathbf{F}=\frac{d \mathbf{P}}{d t}=M\frac{d \mathbf{v}}{d t}$$ So $$M\frac{d \mathbf{v}}{d t} = M\frac{d \mathbf{v}}{d t} - \mathbf{u}\frac{d M}{d t}$$ And $$-...
  23. R

    How to set the Magdeberg hemispheres in motion (propulsion)?

    This is about the famous, classic experiment of Magdeburg hemispheres with the Wikipedia link below: https://en.wikipedia.org/wiki/Magdeburg_hemispheres. "The experiment was designed to demonstrate the vacuum pump invented by Otto von Guericke - but also the tremendous 'strength' of the...
  24. A

    Rocket propulsion explained only through pressure differential

    Fluid can exert force to object(move object) only through pressure and tangential stress caused by viscosity. if we look at balloon rocket ,here is Newton 3 law action-reaction,but this 3 law as usual don't tell nothing how fluid really exert force to the ballon.. it exert through pressure...
  25. A

    Will "centrifugal propulsion" works?

    image veichle with 4 wheels ,beams rotate about point " A",each weight can slide radialy on own "beam" ,so weights rotate in cirlce but with different tangential velocity .Different tangential velocity produce greater "centrifugal force" in one part of circle ,so weight "push" at veichle...
  26. lucas pentland

    Net forces on a boat (propulsion, water and air resistance)

    2500 N [south] + 3200 N [south] = 5700 N [south] 5700 N [south] - 6000 N [north] = 300[north]
  27. Parkerrhees

    Electromagnetic fluid acceleration as effective rocket propulsion?

    Let me preface this by saying I have no background in physics or any of the above other than hours and hours of reading. Could someone explain why (if a method was developed) we couldn't use EFA as a thrust system for a rocket? My reasoning is instead of using fuel to fight gravity and push...
  28. fRod57

    How can I make a simple inductive MHD thruster in water simulation?

    Homework Statement:: Simualte the behaviour of water around an mhd inductive thruster Relevant Equations:: https://www.comsol.fr/paper/download/45837/Pintus.pdf Where can I start this simulation ? What is the required software ? [Mentor Note -- thread moved from the technical forums]
  29. fRod57

    Use of hard drive magnets to build an MHD propulsion ship

    In order to build a small mhd propulsion ship for a physics project, I'm wondering if the magnets we find in hard drives carry enough magnetic field power to function in such an experiment.
  30. M

    Is ablative laser propulsion a better option than Ion engines?

    I’m trying to find something that can replace Ion engines in my Star Wars story. Ablative laser propulsion seems like a good bet because it works in both atmosphere and a vacuum and just seems better than Ion engines.
  31. S

    I Would a rover on an asteroid float away because of the low gravity?

    I’m wondering if a lander/rover landed on an asteroid with a very low gravity, and we wanted to make said rover move around the asteroid, would it “float” away because of the low gravity? Wouldn’t the normal force and the gravitational force equal 0? If we added a propulsion system, how would we...
  32. X

    SpaceX Supersonic electric propulsion systems for airliners

    Tesla+SpaceX= supersonic VTOL suborbital electric jet? “I have an idea for a vertical takeoff and landing supersonic jet.” — Elon Musk, every time the subject of electric planes comes up, to include almost never using the VTOL abbreviation for some reason that’s probably very unimportant. —...
  33. hagopbul

    Weird nuclear propulsion concept

    Hello all: I have a small question about nuclear propulsion , why everyone are trying to use it ,and why this wired choice of nuclear option , retrofitting a nuclear reactor to mount it on the rocket , isn't that a little dangerous , why they don't use other option or research it , there is few...
  34. M

    NASA Which of these methods is the best bet for space propulsion?

    1.) Ion drive 2.) Black hole starship 3.) Fusion Rocket 4.) Fission sail https://en.m.wikipedia.org/wiki/Fission_... 5.) Halo drive https://arxiv.org/abs/1903.03423 6.) Horizon drive https://www.tsijournals.com/articles/pro... 7.) Pitch drive, Diametric drive, Disjunction drive...
  35. M

    Which of these methods of propulsion is “best” for future spaceflight?

    Summary: Which of these hypothetical propulsion methods is the best for a spacecraft during Interplanetary flight? Let’s just assume all at this point are cost-effective at the time. Consider the •Safety of the engine •The speed •The efficiency 1.) Monoatomic hydrogen propulsion 2.)...
  36. X3FeynmanAlfven

    Physics Masters Degrees that eventually lead to a career in Plasma Propulsion

    Hello, just wanted to know what is recommended after undergrad Physics to get into a career developing electric propulsion systems, or anything to do with Plasmas and future propulsion devices?
  37. X

    Fusion aerospace propulsion systems for the near future

    Let’s ditch chemical fuel (even like scramjet, aero spike and SABRE) and venture to the future, for only thus we can become a multiplanetary species, and establish a true interplanetary/interstellar transit system. For atmospheric ascent: 1.Fusion reactor (thermal power)+Thermal ramjet...
  38. Anand Sivaram

    Question About Electric Aircraft Propulsion

    I have been thinking about this subject for some time now, based on the following considerations 1) Many companies are working on Electric Aircraft Propulsion, high energy density Li-Ion batteries are used to power Electric motors and they drive propellers. This is the approach every one is...
  39. Avaro667

    Magnetohydrodynamics Propulsion

    Hey guys. I wanted to ask your opinion about something . I'm interested in MHD propulsion and i know so far that has been inefficient against the usual propulsion systems up to today. Do you think it worths someone getting deeper into it ? I'm thinking how awesome would a practical...
  40. G

    What are the likely first forms of relativistic spacecraft propulsion?

    I've been interested in relativistic spacecraft since news of the Breakthrough Starshot project announcement a few years ago. Breakthrough Starshot's method of laser propulsion still has many technical hurdles needed to be crossed. So I'm wondering what you guys think the first forms of...
  41. anorlunda

    Remarkable New Marine Propulsion Systems

    I recently came back from a cruise on MS Eurodam. The ship was equipped with two 17.6 MW Azipod propulsion systems. The captain explained a bit about them in a Q&A session, and I researched a bit more because I'm curious as an engineer. I'm sharing it here on PF for the benefit of other...
  42. S

    Is black-hole propulsion really feasible?

    Here is a video that dicsusses it, but it sounds awfully science-fictiony to me.
  43. A

    What is the Research Focus of Tony Nelson in Water Dynamics and Engineering?

    Water, is my interest ,in it swimming ,surfing in Sydneys' Pacific rollers to feel the turbulence ,SCUBA , boats, pumps ,pipes, Hydrodynamics, treatment, mini-hydroelectric generation. Currently working on improvements to sculling with unique "scullocks" foils on the blades of oars. Human...
  44. Gabriel Mota

    B Constant Off-Center Propulsion (without gravity)

    Hi, How to calculate the position in time by applying a force, like a Thrust, not in the center of mass: I only know about the linear and angular formulas: Pos/rotation = 1/2 * F * Time^2 I have struggled finding topics about this maybe because i don't know the correct nomenclatures and maths.
  45. A

    How does ion aircraft propulsion work?

    I saw a video on youtube and it explains in a vague way how the system works, so there is a potential difference between two sets of electrodes and air between them is ionized in the presence of the E field but how muhc is it ionized? Because I get the impression that the ionization is not in...
  46. O

    A How are positrons used for fusion propulsion?

    Hi, I recently came across Positron Dynamics, a company working on a fusion propulsion system. You can watch this presentation given at Breakthrough Discuss 2018. They also got a grant from NIAC. Rather than trying to create and store positrons, they use Na-22 as a source. They also patented...
  47. S

    What is the best method for electromagnetic propulsion?

    I mean by the best the one that use the least energy to produce the grater force capable of carrying weights . Say you have a pulley attached to a ceiling with height of 3 meters, around the pulley is a string that attached to a 30 kg weight and on the other side of the string you want to use...
  48. F

    I Paddle convex and concave sides and forward propulsion

    Hello everyone, In stand up paddle boarding, the correct way to use the paddle when moving forward is to have the paddle convex side facing rearward while the paddle pushes water backward. This is explained by the fact that the paddle generates a lift force pointing backward if the convex side...
  49. isukatphysics69

    Solving Squid Propulsion with Momentum Conservation Equation

    Homework Statement Homework Equations p=mv j=Δp[/B] The Attempt at a Solution I am confused as to how to approach this problem. so it looks like squidwards mass is changing from 1.2kg to 1.1kg after he shoots out the water from his butt. I know that momentum is conserved so 1.1*2.7 -...
  50. A

    What to study for ion propulsion?

    What all branches/sub-branches of physics and mathematics are required to atleast understand the technicalities of ion propulsion ? Please elaborate .