What is Force: Definition and 1000 Discussions

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. D

    Effect on net torque and net force on spools

    I think both spools will land about at the spot x (there aren't any horizontal forces causing them to land away from the x). Also, I think student 2 might be the closest to being correct, but I'm not sure if they're entirely correct; isn't it possible that force doesn't only go to translational...
  2. ergospherical

    I Non-"00....0" components of charge density for a spin-s force field

    It is given that the charge density of a particle of charge ##q_0##, world line ##z^{\mu}(\tau)## (and 4-velocity ##u^{\mu}##) in a spin-##s## force field is a ##s##-tensor\begin{align*} T^{\mu \nu \dots \rho}(x^{\sigma}) = q_0 \int u^{\mu} u^{\nu} \dots u^{\rho} \delta^4[x^{\sigma} -...
  3. rudransh verma

    Confusion with force components

    x component of ##F_3## ##F_{3x}= m a_x- F_{1x}-F_{2x}## = ##ma\cos 50-F_1\cos(-150)-F_2\cos90## y component of ##F_3## ##F_{3y}= m a_y-F_{1y}-F_{2y}## =##ma\sin50-F_1\sin(-150)-F_2\sin90## And so on… My question how we can represent it in diagram ##F_1\sin(-150)##. I suppose...
  4. Iwanttolearnphysics

    About steel balls of different masses and net force

    I don't understand why the answer is B. Here's my thinking: Since it wasn't mentioned that there's any other force aside from the drag force, then Fnet = Drag force I know that Fnet = ma, and since they have different masses, Fnet must be different for both balls? Acceleration cannot be...
  5. F

    How a force is amplified in a lever from the standpoint of internal stresses?

    Hello, While trying to understand how a lever truly works and a force can be amplified using a larger lever arm, I read a thread on how levers amplify forces (https://physics.stackexchange.com/questions/22944/how-do-levers-amplify-forces ) and the discussion involves stresses, internal torques...
  6. A

    I Normal force and details of the Earth holding up an object

    It's a simple application of Newton's third law to show that the Earth indeed does accelerate towards an object as it falls towards earth. M_o is the mass of the object M_e is the mass of the earth From the third law (and ignoring air drag): M_e * a_e - M_o*g = 0 (with a up-positive...
  7. vibha_ganji

    B What Happens When The Applied Force Equals the Static Friction Force?

    In my teacher’s notes, it said that when the applied force on an object equals the maximum static frictional force, the object begins to move at constant velocity. My question is if both the applied force and the frictional force cancel as they are equal in magnitude, what force accelerates the...
  8. kara123

    Newton's laws of motion -- Force of gravity on a skydiver

    I think you would do force of gravity= mass x acceleration acceleration of gravity= 9.8 m/s mass 75 kg 75kg x 9.8 m/s =735 N i don't know if that's right but i have no idea how to calculate it after he lands, any help would be greatly appreciated!
  9. jonas_biermann

    B Calculating the torque needed to rotate a drum

    Imagine this: You have a drum with a radius of 12cm, around that drum is a toothed belt which is connected to a motor. The drum weighs 10kg The motor should be placed under the drum How would I calculate the amount of torque needed to rotate the drum I don't have any idea how to calculate this...
  10. DadoNoah

    Calculating force on a syringe plunger for a viscous fluid?

    I'm currently working on a precise glue/resin dispenser, and I'm trying to derive an equation for the force one must exert on a syringe plunger as a function of the desired flow rate Q, and also accounting for the fluid viscosity and the syringe barrel and needle geometry. I've attached a scan...
  11. I

    Lab Experiment - Puck Impact on Wall, Analyzing Force

    Please see attached image. This was a lab performed where a puck hit a wall shown on the page, the difficulty I’ve had is being able to see when and for how long the puck hit the wall as it is needed to find the average force in the system. Each dot on the page is 30milliseconds apart.
  12. lela

    Is the force exerted by a pivot always towards the center of mass?

    I thought that the force by the pivot A on the pole AB would be the reaction force to the x-component of the gravitational force on AB. This would mean that the force by the pivot would be parallel to the pole, but in my notes from class the force vector seems to be more along the bisector of...
  13. Z

    How to calculate differential work done by a force in circular motion?

    My question is, is this correct, and if so, why the minus sign?
  14. Induana

    Gravitational force equals centrifugal force?

    Book says that correct answer is d) but I can't understand why. If the result of gravitational and centrifugal force is 0N then there is no force that would keep those objects inside the spacecraft orbiting around the planet. Or am I just completely wrong? Thank you for your help.
  15. Elementrist

    B Magnetic force driving a small iron ball

    How can I calculate the force from magnetic field of a solenoid, grabbing a small iron ball? I want to use the good old simple F=ma formula in order to calculate the ball's acceleration. But can't find a formula to somehow convert the known field quality (in unit Tesla) to Force (in unit...
  16. Dezzi

    Electric field problem -- Repulsive force between two charged spheres

    I attempt to solve the problem in the picture below.
  17. S

    Bobsled Impulse and Force -- ELASTIC collision problem

    I attempted to do mvf-mvi to find the impulse, but had trouble figuring out what to use as v (where does the angle of 3degrees come in?), and thought that there had to be more to the problem considering the other details I was given. I then attempted to maybe calculate the kinetic energy lost...
  18. S

    I Gravity: Force or Acceleration?

    I’ve watched a few videos recently that explained that gravity is not a force rather it is caused by time dilation because clocks tick slower closer to mass. Objects will follow a geodesic through spacetime and require a force to move them away from a geodesic - so the surface of the Earth is...
  19. P

    Understanding the Coriolis Force: How to Calculate It

    I know that the perpendicular force is the Coriolis force, but I don't know how to get it
  20. V

    Force acting on a charge across a hybrid medium

    The force on charge ##q_2## will depend on the electric field in medium with dielectric ##K_2##. Electric field in this second dielectric due to ##q_1## is ##E = \dfrac {kq_1} {K_2r^2}## where r would be the distance from ##q_1##. So, the electric field at the point where charge ##q_2## is...
  21. C

    Calculate force to open a door with a gas spring

  22. D

    Seemingly simple equilibrium problem - force balance

    For this problem we are asked to find the tension in the cable BE and the compressive force in beam CE. We are given that ## \angle C = 40 \circ##. We are also given that CE = 10 meters and vertical BC = 6 meters. My solution is to find BE using the law of cosines, from which I get $$BE =...
  23. j19063dc

    Finding the resultant force, moment, and x-y coordinates

  24. K

    A Cyclic coordinates in a two body central force problem

    (Goldstein 3rd edition pg 72) After reducing two body problem to one body problem >We now restrict ourselves to conservative central forces, where the potential is ##V(r)## function of ##r## only, so that the force is always along ##\mathbf{r}##. By the results of the preceding section, I've...
  25. S

    I Base Motion and Vertical Beam - Basic Reaction Forces?

    So I am trying to understand how to estimate the amount of deflection [D] the vertical beam shown above would experience if the base it is attached to is accelerating at a constant acceleration [a] of 9.81 m/s. I assume the Force [F] would be equal to weight of the vertical beam (mass x...
  26. 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.
  27. 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...
  28. 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 +...
  29. 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##?
  30. 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?
  31. 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...
  32. 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?
  33. 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.
  34. 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...
  35. 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...
  36. 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...
  37. 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...
  38. 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...
  39. 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...
  40. 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...
  41. 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...
  42. 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...
  43. P

    Is this force diagram correct?

    Trolley should have zero acceleration.
  44. 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...
  45. 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...
  46. 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} =...
  47. 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...
  48. L

    Central force field derivation

    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...
  49. 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...
  50. 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??
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