Force Definition and 1000 Threads

In physics, a force is any influence that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of newton (N). Force is represented by the symbol F (formerly P).
The original form of Newton's second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time. If the mass of the object is constant, this law implies that the acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.
Concepts related to force include: thrust, which increases the velocity of an object; drag, which decreases the velocity of an object; and torque, which produces changes in rotational speed of an object. In an extended body, each part usually applies forces on the adjacent parts; the distribution of such forces through the body is the internal mechanical stress. Such internal mechanical stresses cause no acceleration of that body as the forces balance one another. Pressure, the distribution of many small forces applied over an area of a body, is a simple type of stress that if unbalanced can cause the body to accelerate. Stress usually causes deformation of solid materials, or flow in fluids.

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  1. Nick Tucker

    Calculating Force and Work for a Penguin Climbing up an Ice Slope

    Got a question from my science exam that I'm not sure how to figure it out. All the context I was given is attached. My attempt: Mass=26kg 26a = Force Work = 26a x 2 Work = 52aNot sure how to figure it out, as 52a is the wrong answer.
  2. Rusty_Shackleford

    Push/Pull Force of wheeled cart on an incline

    Summary:: Looking for the formula to calculate force required to push a wheeled cart weighing 227 kg up a 15 degree incline. I’m trying to find the formula for force required to push a 227kg cart with four wheels up an incline that is 15 degrees. From my physics classes I thought the formula...
  3. D

    Maximum force applied to prevent block from sliding up ramp

    I tried using Newton's first law as the net force in both the x and y directions should be zero in this case. In the free body diagram you need to consider weight, friction, normal force, and the horizontal force. I got a result that said that the horizontal force F you apply is at most W(mu_s +...
  4. M

    I Build Setup to Create Electric Damping Force

    Hello! Is it possible to build a setup (containing time dependent and independent electric fields), such that a charged particle will feel a force proportional to its velocity i.e. ##ma = -\alpha v##?
  5. N

    B Electromagnetic force of Electrons

    If you could command all the electrons in an average human body and get them to spin in synchronicity (a clockwise circle in the horizontal plane) how much magnetic force does that produce? Would it create a force against gravity and make you feel lighter? How much lighter?
  6. L

    Gravitational force - I translating the wording into the formula

    i spoke to my proffesor about it but all he said was to put 1 in m1 and m2... for r^2 since it says to quadruple to just put 4^2 I asked about the G in the equation but he said not to worry about iit and pretend its not there...
  7. C

    The Force components acting on an object

    Another user suggested adding the forces in the x and y direction then dividing by 1.4. Doing this for A) gave me 4.285 which was wrong any suggestions?
  8. fascinated

    I Calculating Force Needed to Pull Bungee Taught

    Summary:: How would I calculate the necessary force? Let's take an example where the bungee is 1000 feet long and weighs 9 pounds. How much force would be needed to pull it taught across a horizontal plane? Thanks for any help.
  9. S

    B How does curvature of spacetime affect the motion of test particles?

    If I had a chart of Cartesian coordinates and it had four axis's, t, x, y and z, how would I induce motion of a test particle by curving those axis's ? If the test particle was standing still and only moving in the t axis, how do i get it to move in the other axis's, x, y, z. I can understand a...
  10. H

    Amusement Park Centripetal Force Question.

    Hi, I just had a question about this homework question. I am not given the mass at all in any portion of the question. Fs = Fc because the static friction is the thing that keeps the rider stuck to the wall My answer came out to about 3.4 m/s for the minimum speed that keeps the rider stuck to...
  11. S

    Force exerted by rod on a mass moving in vertical circle

    (A) and (B) are obviously wrong but I think both (C) and (D) are correct. At the top, the forces acting on the mass are tension and weight, both directed downwards so the equation of motion will be: $$\text{Tension}+\text{Weight}=m.a$$ $$\text{Tension}=m.a-\text{Weight}$$ Based on that...
  12. B

    How to Measure and Display Rapidly Varying Vertical Forces from a Rotating Mass?

    how do I measure a rapidly and cyclically varying vertical force I have a rotating mass that generates centrifugal and aerodynamic forces. I want to see the variation thru one rotation at steady state. how do I measure the vertical force generated and display it on my computer screen, with a...
  13. Slipjoints

    Finding Radial Force from Free Body Diagram

    I have a question regarding a homework exercise. My professor asked me to find the radial force in the free body diagram in the image included. There is a weight Fz from above and it is assumed that it is countered by the vertical component of both the Ff (friction force) and the Fn (normal...
  14. S

    Force diagram of two rods hinged together

    Picture from the question Options: Option (B) is wrong because the both reaction forces have to be slanted since they are resultant of normal force and frictional force. I think option (C) is wrong because taking the point where the two rods meet as point P and comparing the torque produced...
  15. M

    Magnitude of the Projection of force "F" on the u-axis

    So I was watching a YouTube video preparing for a quiz on Wednesday, and I saw something that I would like clarification on. I'm pretty sure I understand what is being explained, but I just want to confirm. The figure above is associated with the problem at hand. So I understand that to get the...
  16. mmcnaught831

    How to translate force into upward hinging motion between two panels?

    Pictured below are two hinged panels that can rotate upward to form an upside-down V. In position 1, the panels are lying flat. In position 2, the panels have folded together and the joined edge is raised up. Normally, in order to actuate this hinging motion, one would need to manually lift the...
  17. wysocki

    How much force to tip over an umbrella stand?

    I'm working on a project where I have an upright post secured to a flat square base (similar to an umbrella stand). I want to know how much force would be required to start it to tip toward its left edge. Here's an illustration where the base is 10" square, 1" thick and weighs 50 lbs. There is...
  18. P

    Is the Force Diagram for a Trolley with Zero Acceleration Accurate?

    Trolley should have zero acceleration.
  19. B

    B Why don't boxers' skulls shatter from the forces of punches?

    Hi All, My question is in relation to forces that can come through movement. For example, the skull is stated to take around 520 pounds of force or around 2000N: https://www.virginialeenlaw.com/help/how-much-force-can-a-human-skull-withstand.html However, boxers can punch well in excess of...
  20. R

    Force of pressurized water exiting a hose or pipe?

    Well known examples of the force produced by pressurized water exiting a pipe: JetLev Water Propeled jet Pack. Hovering Car. I need to calculate the maximum for the thrust produced when the hose or pipe is bent rearward. Since this is similar to the case of a water bottle rocket, the guess...
  21. L

    I Relativistic Force & Velocity Relation to Acceleration

    According to this link here https://en.wikipedia.org/wiki/Relativistic_mechanics#Force , we can inverse the relation of force in terms of velocity and acceleration: $$ \mathbf{F} = \frac{m\gamma^3}{c^2}(\mathbf{v} \cdot \mathbf{a})\mathbf{v} + m\gamma\mathbf{a} $$ to get: $$ \mathbf{a} =...
  22. S

    Magnetic energy density, and pressure due to magnetic force

    Hi, The problem I am working on requires me to work out the the pressure on the outer conductor of a coaxial cable due to the current on the inner one. This cable carries a dc current of 5000 Amps on the inner wire of radius 2 cm. The outer cylindrical wire of radius 5cm carries the return...
  23. L

    How can one derive an expression for \( w^2 / k \) using \( b, p, l \) only?

    The total energy of the particle is ##u^2 / 2 - k/R##. When ##u^2 \gg 2k/R##, we take the total energy to be ##u^2/2## only. By the conservation of energy, we have: $$ \frac{u^2}{2} = \frac{w^2}{2} - \frac{k}{p} $$ Take the angular momentum expression ##l = bu##, we can replace ##u## with...
  24. timotola

    I Drawbridge falling before caught by rope/cable - Max force

    Hi, I'm currently looking into the forces exerted on a cable if the cable was to go from slack to taut due to a falling object that is pivoted about a lower hinge - such as a drawbridge but instead of slowly lowering, there is slack in the cable causing the bridge to freely rotate about the...
  25. Mr.Husky

    B How is the acceleration proportional to the removed force?

    Image above is the question. Below image depicts solution. if F1 is removed then the acceleration of that mass must be sum of accelerations of remaining forces. Right?? But answer says that acceleration of that mass is equal to acceleration of F1. I don't understand it. Can someone explain it??
  26. grandpa2390

    Block on a Spring, Nonconstant Net Force

    Just to be clear, this isn't a homework problem. it is an example problem found on page 68 of the text "Matter and Interactions" 4th edition. The solution is given in the book, but I'm having difficulty following their reasoning. according to the book the net force is not constant, therefore we...
  27. ayans2495

    2 Dimensional Motion: Net force at an angle

  28. Boltzman Oscillation

    B Deriving formula for force by thought experiment

    Hi all, I was thinking punching a round ball on a flat surface and seeing how I could determine a formula for force from it. I thought the following: 1. The ball will go further the harder I punch and thus force must be proportional to displacement d. 2. Ball will go further if it is lighter...
  29. Istiak

    Why position times mass is equal to 0 here (vanishes)?

    $$\sum_i m_ir_i$$ Why the term always vanishes? There's some more equations where the mr was vanished. But, they didn't explain why it vanish. Why the term vanish? I think that's for position 0,isn't it?
  30. LarryS

    I What types of forces are described in the standard minimal QED Lagrangian?

    In Q.E.D., the electrical part of the Lorentz Force between unlike and like charged particles is realized through the absorption and emission of photons. How is the magnetic part of the Lorentz Force realized in Q.E.D. via photon activity? As always, thanks in advance.
  31. P

    Force & Energy Changes of Air by Helicopter

    Solution 1: Force on air = Force on helicopter. ##F = \frac {dp} {dt} = v \frac {dm} {dt} = v^2 \rho A## ##P = Fv = \rho A v^3## Solution 2: Power from helicopter converted to rate of kinetic energy increase of air ##P = \frac {dE} {dt} = \frac {1} {2} v^2 \frac {dm} {dt} = \frac 1 2 \rho A...
  32. Istiak

    Why used $\cos\theta$ for $\text{y}$ axis or, gravitational force?

    >![figure 3.2](https://physics.codidact.com/uploads/B5XdWq6GbB4vwyADQdALaCrC)![figure 3.1](https://physics.codidact.com/uploads/pkmWFgoesvQaiAfv5yKj6ynB)<br/> >Mass M1 is held on a plane with inclination angle θ, and mass M2 hangs over the side. The two masses are connected by a massless string...
  33. MichPod

    I Calculating Force & Acceleration in Electrostatic Field (B=0)

    For a case of electrostatic field (B is equal zero), how should the force acting on a moving charge be calculated if we want to take into account all the relativistic effects? Also would it be correct to calculate the acceleration of the charge as a=F/m, or should some other formula be used? For...
  34. M

    Change the application pole of the moment of a force

    Good morning everyone! I am an aerospace engineering working on my thesis and i am trying to solve a little problem. In the picture you can see an "aeordynamic" body. The CFD analysis gives me the forces and the moments acting on this body. How can i calculate the momentum acting on the body...
  35. E

    B How to determine force based on pressure

    Hello In a pharmaceutical lab,a certain pressure is applied to IV bags using the equipment shown below.We need to calculate the force acting on the bags based on the applied pressure.I know the formula is F=PxA.But i am not sure what the surface area is.Should i take the whole surface area of...
  36. F

    I Questions regarding traveling speed in time and gravity as a force

    I am an Engineer, so I have some knowledge about physics and calculus. I've seen relativity in university years ago but only briefly. The majority of my knowledge in SR and GR, which isn't much, are from reading, studying and searching online myself. I have seen some definitions that I am not...
  37. Sagittarius A-Star

    I Force on Scale in Rocket Scenario: Calculation & Discussion

    [Moderator's note: Spin-off posts from previous thread have been included in this new thread. Also, the OP's re-post of the scenario for discussion has been moved to this top post for clarity.] Yes. Physically, scales measure a force (and indirectly the energy) in their frame. Consider the...
  38. N

    B Why do moving charged particles feel a force in a magnetic field?

    When I read things about magnetism on internet, I don't understand at all about one thing: If a moving particle receive a force if it's in a magnetic field, so it should accelerate, so what happen if we change the referential so that the particle now don't move? The particle shouldn't receive...
  39. S

    [Electrical force] 2 balls hanging from ceiling, angled

  40. nomadreid

    Medical Is a small tidal force on the body harmful over the long term?

    In the following page (which, despite examining a question that comes up in science fiction, raises valid scientific questions): http://pages.erau.edu/~andrewsa/sci_fi_projects_spring_2015/Project_1/Eilts_Mitchell/Enders%20Game%20Eilts/Enders%20Game%20Eilts/index_Eilts.html I encountered the...
  41. S

    [Electrical force] Electrical charge in equilateral triangle

  42. S

    [Electrical force] 2 balls hanging from ceiling

  43. R

    Force Diagrams for a Combined Mass

    I know that the ##F_{AonB} = -F_{BonA}##, but I just wanted to check something. If object A is the truck, then the x-direction should have a vector coming from the force of the engine driving the truck forward, a vector pointing in the negative direction for friction, and a vector in the...
  44. Shreya

    Force on a dipole in a non uniform electric field

    I have figured out how the force is towards left in the first case. I think it is due to the larger force on - charge. Please help me out with the second and third case.
  45. J O Linton

    B What is the distance at which gravity and the cosmological force are equal?

    In considering the excellent answers given to my previous query about a photon in a box, I was led to consider what force was needed to hold the walls of the box stationary (w.r.t. an inertial observer inside the box.). If you place a mass m on the end of a very long string of inextensible...
  46. Einstein44

    Calculating Magnetic Field Strength and Force of Eddy Currents in a Solenoid

    I have jus thought about how maybe I could sue the magnetic field strength equation for a solenoid (that I used to find the Emf in the first place) again, to find the magnetic field strength arising from the induced current: B= μNI / L where μ is the permativity of free space N= Number of...
  47. S

    Calculation of the lateral force of a trailer coupling

    Hello, i´ve got a problem with the calculation of the forces on the hitch of a vehicle and a trailer. I do need the lateral force on the hitch for the calculation of my single track model of the vehicle and trailer. I have a longitudinal model of the vehicle and the trailer. My input signal...
  48. P

    B How do I express the force of me falling 33 feet onto concrete?

    I weight 90.7kg. I fell 10.05m landing on soild concrete. how do I express the "power of my impact? in G-force? A relitive weight? I am self taught in very basic physics after a high school education.
  49. Paige_Turner

    B The Impact of Tidal Force on a Star's Magnetic Field and Supernova

    And if a star is severely stretched by tidal force, how does that affect its magnetic field and the process of it collapsing at the start of a supernova?
  50. tmalcolm

    Force pressure variance after hole is plugged?

    There is a tall cylinder filled with water. And there is a 3 in diameter hole near the bottom and water is gushing out. (assume the cylinder is continually being re-filled from the top) You work to plug the hole with a 10 inch long cylinder that is exactly the perfect diameter fit to plug the...
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