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.

View More On Wikipedia.org
Recent contents Top users
  1. Luja

    B Understanding Newton Force: Real World Examples

    I would just like to get a perspective on how much is an x amount of Newtons, like in real world examples. I know everyone says 100N is about equal to the force of a 10kg object being set on you, but this example really only gives perspective on downwards force. For example I calculated the...
  2. H

    I Force due to acceleration and time flowing differently

    in special relativity we have moving reference frames resulting in a different flow of time in each reference frame. This we can explain because we use the fact that the speed of light is the same in all reference frames, leading to the Lorenz transformation giving the amunt of slowdown of time...
  3. V

    B How does exchange of elementary particles result in a force?

    Homework Statement:: I came across the following in an online article. I am unable to understand how these elementary particles cause a force to exist. "Each of the four forces results from the exchange of force-carrier particles.". Above statement is taken from...
  4. V

    How can the force of a normal reaction be electromagnetic?

    I do understand that gravitational the electromagnetic force between two electrons or protons is very large compared to the gravitational force between them. I can see this by looking at the equation of gravitational force (##F= \frac {Gm_1m_2} {r^2}##) and the equation of electrical force given...
  5. L

    Conducting rod in equilibrium due to magnetic force

    I am having problems understanding point (b) so I would like to know if my reasoning in that part is correct and/or how to think about that part because I don't see how to justify the assumption ##v_y=0\ m/s##. Thanks. I set up the ##xyz## coordinates system in the usual way with ##xy## in the...
  6. R

    B Mathematics involving a gravitational force

    It's been more than 60 years since I attended high school, and I am trying to learn and understand concepts in Newton's physics that were not taught and were not part of the school curriculum during the 1950's. It is my understanding that the current mathematics taught and used in our...
  7. F

    I General expression of wind force on a sail....

    Hello everyone, In trying to better understand how sailboats work, how they can sail upwind (not directly), how the go faster than the wind speed, I have been thinking about the magnitude of the wind force and its equation: $$F_{wind}= \frac {1}{2} \rho_{air} A v_{wind}^2$$ Instead of ##...
  8. link223

    Friction Coefficients: Determining Force Direction?

    Do I determine this from the friction coefficients? Such that because mu_b > mu_a I know that it'll push on B because it has a bigger friction coefficient. such that this has nothing to do with the mass of the blocks? or does it? f.e. can I take it to be in an arbitrary direction and then...
  9. pandatime

    Work done in elevator problem — is it positive or negative?

    Hi! So, I've actually already solved this problem.. for the most part. I have split up the work into two sections, floor 0 to 10, and floor 10 to 15. From floor 0 to 10, I did ## F_{elevator} = w_{pass.} + w_{elev.} ## ## F = (70)(20 (num. of pass.))(9.8) + (800)(9.8) ## ## F_{elev.} = 21560N...
  10. Jun

    How can I calculate the maximum impact force on the helmet?

    I am studying the force that helmets have to withstand. If I drop a 5kg head model and helmet at 1.064m on an anvil and the impact time is 0.005 seconds, how do I get the 'maximum' impact load on the helmet?
  11. T

    A Is Gravity Just the Electrostatic Force?

    I read this paper and this is iindeed a very interesting hypothesis. The implications of this theory if true are enormous! Please comment! Is Gravity Just the Electrostatic Force? <crackpot link deleted>
  12. pandatime

    Finding the Right Spring Force: A Tale of Error and Redemption

    What I've done so far is find the spring force through ##F_s = -kx## ##F_s = -111*16.7## ## = -1853.7N## My conclusion was that since this is the spring force, the tension force must be just the negative of that so ##1853.7N## because the net force has to balance out, but I am horribly...
  13. mcconnellmelany

    Investigating Lagrangians and Constraints for Tension Calculation

    I had used the same constraint as the solution manual says. So my two Lagrangian would be ##L_1=\frac{1}{2}m_A\dot{x_A}^2+\frac{1}{2}m_B\dot{x_B}^2+\frac{1}{2}m_C\dot{x_C}^2+m_Cgx_C+T(x_A+x_B+2x_C-c)## whereas c is just a constant. Of course, I have to write my Lagrangian using constraints...
  14. Rikudo

    Distribution of normal force in this problem

    It is crystal clear that we need torque equation to solve this. But, in order to do so, I need to know where the normal force is located. As far as I'm concerned, normal force is not distributed equally. If this is true, then I suppose this problem is unsolvable? (Though the book says thay it is...
  15. M

    Upward force of float moving in an arch under water

    a float with 5 pounds of water displacement is resting on the bottom of a pool of water 10 feet deep. The float is tethered to the bottom of the pool via a string that is pulled tight lengthwise and so is also laying on the bottom of the pool. The string is 4 feet long. If the float is...
  16. jackmrrabbit

    I Calculating Hydrostatic Force on valve cavity in a Solenoid Valve

  17. mcconnellmelany

    Find dissipative function for the non-linear force f=-bv^n

    For a nonconservative force, What would be the dissipative function for a force f=-bvⁿ in Lagrangian (Where v is the velocity) [#qoute for a nonconservative force f=-bv The dissipative function is D=-(1/2)bv² ] Since ##f=\frac{\partial D}{\partial \dot x}## so the dissipative function should...
  18. L

    B Wanting to do some impact force experiments

    I have 3d printed some 25mm cubes all with the same parameters. what i want to do is take some different weight dumbells, and drop them all from half a meter onto a cube. My goal is to collect data and see at what impact force the cube fails. For me, failure will be when layers break apart, not...
  19. Victor Correa

    I Terminal Velocity proportional to the Drag Force 𝑚𝛾𝑣² in free fall

    Can anyone help me? I know that's wrong, but i don't know where. Thanks for your attention so far.
  20. StoneBored

    How to get the transfer function for force transmissibility of a wall?

    Hi, I am trying to get the transfer function from a wall between rooms. From one side I have the force of a hammer as an input ,and in the other side of the wall (next room) I have an accelerometer. Is it possible to get the TF without know the damping, stiffness and mass of the wall partition...
  21. Y

    I What is the minimum force required to lift an object?

    A person stands on a scale. The scale reads his mass 60 kg . Now this human moves up his body short distance like someone tries to pick a fruit from a tree. The scale will start to increase by small forces x N in which the total read of the scale is 600+x N *. The force he exerts on the scale is...
  22. Svelte1

    How is the slope of the shear force equal to the negative of the load?

    At any point between A and C the point load is negative (downwards), in the shear force diagram: positive is upwards, so this slope is negative. The equation says the slope should be positive. Is this something to do with shear force sign convention?
  23. A

    I Translational force of a pulley

    Below is a pulley with mass and a string around it where the tension of one end of the string is 20 N and the tension of the other end of the string is 60 N. I know there is a net torque due to the differing tensions of the string, so I am wondering what the translational forces are on the...
  24. mcconnellmelany

    Is it possible to find Tensional force from Lagrange?

    Lagrangian principle is easier to solve any kind of problem. But we always "forget" (not really. But we don't take it into account directly.) of Tension in a system when looking at Lagrangian. But some questions say to find Tension. Since we can get the equation of motion from Newton's 2nd law...
  25. C

    B Newton's third law (equal and opposite force)

    Something about Newton's third law confuses me, when I hold my phone and I move it around it's velocity is changing, therefore because Newton's first law it's acted on by a force, and because Newton's second law, the force is directly proportional to the mass and acceleration of that object...
  26. C

    I How Does Centrifugal Force Affect Objects on a Rotating Disk?

    I believe I understand centripetal force, acceleration is necessary for something to spin in a circle because things normally want to continue moving in a straight line (Newton's first law), so a force is necessary to keep something rotating. If you have an object fastened to a rotating disk it...
  27. S

    A Motorcycle, the force exerted upon from collision

    Synopsis, The insurance company wants to repair this 3-year-old motorcycle with 3400 miles on the odo father taking this hit. The motorcycle was modified with an aftermarket "engine guard," which was made out of powder-coated steel tubing and bolted directly to the frame which is made out of...
  28. D

    Home project: Kilogram Force on wheel bearings

    Hi all. I'm designing a custom spare wheel carrier for my 4wd and currently seeking knowledge on which bearings to use, so I need to work out what force on the bearings will be when it's open (closed will be locked and fully supported!) The example image is simplified for calculation. Close...
  29. C

    Difference in clamping force between bolts and screws

    Hi everyone, I’m trying to figure out the clamping force of a set of screws that thread into a plate. My question is: Would this calculation differ from calculating the clamping force of a bolt with a nut? What would be the difference in how the fasteners/members would react to a tensile...
  30. N

    B Centrifugal force spinning Basketball

    Hi, Looking for Centrifugal force on water droplets on my spinning Basketball at 33 RPM, 45 RPM and 78 RPM
  31. A

    Understanding Driving Force in the m2 Equation: Explained by Experts

    I am having trouble understanding why the second term in the m2 equation, b1(x'2 - x'1), is a negative term. Given that this force is the reason why m2 is moving in the first place, why is it not considered a driving force? I think that I don't have a clear understanding of what driving force means.
  32. N

    The connection between potential energy and force

    Hi, if the force is the derivative of potential energy, does it mean that the force is equal to mg and with a constant gravity, it will be the same at any height? But in real life, F (or mg) would be different on the Earth's surface and 400 km above it (~8 m/s^2). So, this formula is used to...
  33. T

    I What is the relationship between force and potential in particle interactions?

    Suppose I have some interaction potential, u(r), between two repelling particles. We will name them particles 1 and 2. I want to find the force vectors F_12 and F_21. Would I be correct in saying that the x-component of F_12 would be given by -du/dx, y-component -du/dy etc? And to find the...
  34. correction_tape

    Finding the Magnitude of the Force Acting on an Object

    So far, I've only attempted the first number: F = (4kg) [(-4+2t)-0]/t ? Been thinking how to cancel out the time, but I really have no idea how to proceed. Was I supposed to cancel it even? Can someone please help and tell me how you would answer this? (And maybe show a solution as well so I...
  35. Y

    Graphical Impulse calculation from the graph of force verus time

    hello i would like to get some help with this problem. At first it try to calculate the impulse by the area but i found it too difficult Then i try to solve it by the forumla J= F(t-t0), but the problem is that i don't know what F is so i try to solve it like this F10) = 8 F(33) = -13 so EF =...
  36. chane

    The necessary inclined force to rotate an object around an axis

  37. ROOT0X57B

    Force of brake pads on a wheel

    [Mentor Note -- thread moved from the technical forums to the schoolwork forums] I have a hollow-cylinder wheel model, braked with brake pads located at a distance d of the wheel's center axis. The brake pads have a contact area S. They are also forced towards the wheel with a pressure p. The...
  38. alejo ortega

    Resistive force exerted on a sphere (air resistance)

    i don´t understand the question
  39. L

    Force to apply to a loop moving away from a current-carrying wire

    What I have done: (1) ##\Phi(\vec{B})=\int_{S}\vec{B}\cdot d\vec{S}=-\frac{N\mu_0 il}{2\pi}\int_{s=h}^{s=h+l}\frac{ds}{s}=-\frac{\mu_0iNl}{2\pi}\ln(\frac{h+l}{h})## so ##\mathcal{E}=-\frac{d\phi(\vec{B})}{dt}=-\frac{\mu_0iNl^2v}{2\pi h(h+l)}## so...
  40. ols500

    Linking moments with friction force for a sliding block

    Hi so with this question, I am really confused. Even from the start. Like it doesn't tell us where the force is acting on. From top of block, middle of block etc? And I know how to determine the direction of moment for something on a pivot, not in this scenario though. The answer is A. They did...
  41. LCSphysicist

    Understanding the Radial Attraction Force between Two Electric Dipoles

    I am extremelly confused with this question: Basically suppose we have two electric dipoles, parallel to each other, as follows in the figure: I am supposed to show that the force is attractive and radial. But I am not getting how it can be radial (pointing toward each other)! See, the force...
  42. Yossi33

    Need Help with Physics Moment and Force Questions

    hello, i struggle with this kind of questions and i don't understand the way of thinking and how to solve this. in the first picture i don't understand why Moments about point Aare a*F1 because there is the 2 P forces that do moments.? in the second problem i can't understand why there are 3...
  43. A

    B Gravity-like Force: Is Another Force Weaker Than Gravity?

    Is it true that if there was another force similar to gravity (dependent on the stress-energy tensor) then it would have to be weaker than gravity? If so, why?
  44. J

    I Momentum, impact force and Earth

    Suppose two objects, A and B, with large lengths LA and LB, and masses MA and MB, collide at time t0. Both objects before collision are vertical and aligned concentrically, being object B positioned initially at a higher z coordinate than object A. The bottom end of object A is rigidly...
  45. M

    B Angled Rod w Float Attached -- Force of Float

    Hi! A ridged rod is submerged in water at a 45 degree angle toward the bottom of a tank of water. The upper end of the rod is fixed to a pivot point and so, the lower end of the rod is able to move around that pivot point. The lower end of the rod has a float attached to that displaces 50lb...
  46. Pipsqueakalchemist

    Mechanics of machine force analysis with analytical method

    So I was looking at this example problem in my textbook and I don’t understand how they got -168.1 degrees. The part I’m confused with is the first part of the 2nd picture, there’s a coma in the inverse tan, I don’t know what that means.
  47. S

    Calculate the charge on an oil droplet

    The book gives an answer of Q = 3.2 x 10^-19C I get an answer of 6.67 x 10^-19C. Workings below:
  48. E

    Yes! Calculating Friction Coefficient

    Fg = m * g: Fg = 30 * 9.8 = 294 N Fnet = m * a: Fnet = 30 * 1.2 = 36 N Fax = Fnet + Ff: Fax = 36 + 10 = 46 Fa = Fax / cos(angle): Fa = 46 / cos(25) = 50.75 Fay = Fa * sin(angle): Fay = 50.76 * sin(25) = 21.45 Fn = Fg - Fay: Fn = 294 - 21.45 = 272.55 Ff = mu kinetic * Fn, solving for...
  49. A

    I If there is no force being applied can there still be a net force?

    If there is no force being applied can there still be a net force? For example, supposed you apply a force F forward on an object on a frictionless plane, the moment you stop applying the force, the object may still be accelerating towards its final velocity but there is no applied force. So if...
  50. D

    B Creating Artificial Black Hole: Force Requirements

    In a hypothetical deep space experiment in the distant future with appropriate safety precautions in place, how much force/power/energy would be required to create an artificial 1000kg black hole? I haven’t the faintest clue & this isn’t for homework. Where would I even begin looking for an answer?
Back
Top