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

    Problems about magnetic field, electromotive force, induced current

    Hi, I was practicing some problems on the magnetic field and the electromotive force, when I got stuck on these two exercises. Could you help me figure out how to proceed? In the first problem, I tried to find the magnetic field flux by multiplying the induced current for ∆t and R. Should I now...
  2. P

    Does "internal force" have 2 meanings in physics?

    My understanding is that gravitational fields produce an "internal force" (weight) on objects and hence gravity cannot change the total mechanical energy of an object. But in a free falling situation there is no other internal force cancelling it out, so it does not seem to be an internal force...
  3. T

    What is the Correct Distance with Force from Both Sides?

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  4. P

    Using Lorentz Force to derive V = E/B

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  5. Vash25

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  6. E

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  7. F

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  8. L

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  9. Ale_Rodo

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  10. R

    How to find electromagnetic force between nucleus and electron?

    Hello, I'm new here and honestly I'm not a physics student. I'm studying engineering and so, understand little of physics. I am trying to find the bond force of graphene's free electron. That means, the electromagnetic force by which the electron is bound to the nucleus. I can only calculate it...
  11. L

    Mass vs Mass as a Force (Weight)

    Been thinking about mass today and came up with a question. Why is that objects on this Earth describe its weight in Kg, g, mg, Mg? IE 2.2Lbs is 1Kg. So why do we name the 1Kg to be mass, but the 2.2Lbs we call weight. Both have to be a unit of force if there is a conversion factor between the...
  12. B

    How to solve mass-spring system when affected by torque in a pulley?

  13. V

    How to get gravitational force on a gaseous particle?

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  14. Max2020

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  15. silverrahul

    B Force between 2 Point Charges Across Frames

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  16. H

    Verifying Force Calculation Methods: 1/2 mv^2 vs. m*a

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  17. guyvsdcsniper

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  18. V

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  19. B

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    I've gone about getting the arclength S = 1.103m The formula for average force is F = m * (Vf – Vi) / t I know the mass and the initial velocity, but I don't know where arclength comes into play. I'm assuming Vf and T is referring to the moment that the ball leaves the pitchers hand, but I...
  20. imbadatphysics212

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  21. K

    I Is gravity action at a distance or is it a local force?

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  22. J

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  23. NoFaceJack

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  24. H

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  25. Hacker Jack

    B Scientists may have discovered a new force of nature?

    Thanks to BBC for making it readable for a layman link to the article: https://www.bbc.com/news/56643677
  26. M

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  27. cel123456

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  28. E

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  29. V

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  30. appmathstudent

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  31. TonyCross

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  32. O

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  33. Kaushik

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  34. J

    Capacitor exercise -- Calculate the force needed to withdraw the dielectric

    First, I think that I need to calculate the capacitance. It is ## C=\epsilon_0*\frac{l*w}{d}-x*\frac{w*\epsilon_0}{d}+\epsilon*\frac{x*w}{d} ##. After that I should calculate the potential energy. It is ##U=\frac{1}{2}*C*V^2 ##. After that I should take its gradient to get the force. So ##\vec F...
  35. D

    Confused about some basic mechanics principles (force , PE)

    Hi - i am confused about the following basic mechanics principles Consider a large cubic mass ( mass M ) on the ground with a small cubic mass ( mass m ) placed on top of it. The surface between the 2 masses is frictionless 1 - if a push (apply a force ) to the large cube does the upper...
  36. P

    Magnetism used as a repulsive force

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  37. O

    B Gravitational force between two masses

    Hello everyone. Probably this question is trivial, but nevertheless I am confused about Newtons law of motion: $$F=G\frac{m_1m_2}{r^2}$$ Now, some sources say, that F is the force between the two masses m1 and m2. Other sources say, that F is the force that m1 exhibits on m2. But isn’t this a...
  38. yourheartandsoul

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    I figured out that the pressure is 8.0442x10^7 Pa and I’m not sure how to approach the second half of the question. I’m thinking I use the formula F=PA but I’m realizing it’s not saying that .15m is a diameter or a radius.
  39. R

    Force required to drive a fence post into soil

    Homework Statement:: what force is required to drive a 6ft(1.8 m) 4 inch (100 mm) post 2 ft into the ground? I'm wondering how different soils affect driving ability and where I could find information on soil resistive force. A 20 ton hydraulic tractor mounted cylinder is used to press the...
  40. H

    What is the force exerted by the pivot on the stick?

    If exerted a force at 60 cm, should the force F2 be the opposite direction of F1? Thanks!
  41. H

    The magnitudes of the applied force F and the frictional force f of a wheel

    I calculate in this way as follows and get a correct answer. Howere I am not sure if I am using the right way. F R = (½ MR^2 + MR^2 ) a/R F = 3/2 Ma F - f = Ma f = 3/2 Ma - Ma = Ma/2
  42. rcgldr

    I Rail gun - point of application of force?

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  43. bo reddude

    I Physics of exercising and forces felt

    Let's imagine an ideal scenario where you're lifting your own weight in its entirety. Let's say a woman weighing 100 lbs. Suppose she's doing an idealized handstand and pushup from that position. So she's lifting 100 lbs. Let's say ideally all of the forces are on her arms only. Do these forces...
  44. P

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    I have 2 methods, which give 2 different solutions: Let sigma = charge per unit area Let plate 1 be the left plate, plate 2 = right plate. Method 1: Because they are insulating, consider the electric field at 3 regions; region 1 to the left of plate 1, region 2 between the plates, and region 3...
  45. P

    Why is the pressure on a charged sphere only exerted on the contact area?

    The force per unit area (Pressure) on a part of the sphere is given by F = (E outside + E inside)/2 * Q = 0.5 (kQ/R^2) * (Q/ 4piR^2) = (Q^2/ 32pi^2 e0 R^4). I understand the above line. The solution then says this pressure is exerted on the contact area between the 2 spheres, as given by...
  46. P

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  47. M

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  48. Goz83

    I Force required to open a swinging gate

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  49. J

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    I accelerate charged particle ##A## causing virtual photons to travel to distant charged particle ##B## which feels an electromagnetic force proportional to ##A##'s acceleration (for a classical field description of this effect see https://www.feynmanlectures.caltech.edu/I_28.html Eqn 28.6)...
  50. hquang001

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