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. S

    Gradient Force of an optical near field

    Source: Principles of Nano-Optics, for Lukas Novotny and Bert Hecht.The equations above represent the electric field in the second medium when a light hit a surface and the condition of TIR (total internal reflection) is satisfied. Actually this is what called Evanescent field. The point is if I...
  2. Saptarshi Sarkar

    Energy of particle when under a central force

    I calculated the potential energy of the particle as follows : But I am not sure how to calculate the kinetic energy. I know that if it was a satellite orbiting a Earth, I could use ##\frac {GMm} {r^2} = \frac {mv^2} {r}## to calculate the velocity v and they I could calculate kinetic energy...
  3. bravopipo

    Maximum load capacity of a time dependant Force on the surface of a metal

    Hello; What equations on mechanics can I use or study in order to measure the maximum force in Newtons the surface of the metal Steel box can hold. Details: Watch the image below, we have a metal box made of let's say steel, this box have a shape of rectangle of a thickness of for example 1cm...
  4. A

    Opposing force of the axle when a torque is applied to a wheel?

    Okay let's say we have a wheel attached to a fixed axle, free to spin, ignore friction and we apply a force on the edge of the wheel. That force creates a torque, does the axle have an opposing force to keep the wheel/axle assembly from accelerating linearly? Ive learned on this forum that when...
  5. Vivek98phyboy

    Force due to Surface tension here

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  6. T

    What force causes a balloon to float?

    When I blow a balloon with CO2, it falls as it is heavier than air. Then it is gravity that causes the balloon to fall. When I buy a balloon filled with helium gas from a store, it floats as it is lighter than air. But what force is causing the balloon to float?
  7. JD_PM

    Central force on a particle following a logarithmic spiral

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  8. O

    I Force on a rigid body inside a liquid flow

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  9. Roundandround

    Unraveling the Mystery of Mass & Force: A 180 lb Person

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  10. cemtu

    Classical Mechanics: Linear movement against a constant force

    I solved this question until the end of the "c)Find the distance until the boat completely stop" However I can not solve the integral I encounter in the solution of the last part of c). Would you please check for math and maybe my mistakes and tell me what to do? Here:
  11. cemtu

    Classical Mechanics: Finding the centripetal force acting on an object that moves within a spiral orbit.

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  12. C

    What is the tension force at the top of a spring?

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  13. Amoghgirgaonkar

    The Mystery of Purple Objects: Understanding Electromagnetic Force

    ans is opt4
  14. U

    Linear Force to Torque Conversion

  15. Saptarshi Sarkar

    A particle of unit mass moves under the action of force F=-k²/x³ ....

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  16. Q

    Coupled pendulum with external force?

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  17. K

    B Resistive force that a nail will have to overcome to penetrate a piece of wood

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  18. Hajarmq

    Rotation and spring force exercise

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  19. D

    Getting Force with distance, mass and time

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  20. A

    Force of the Ladder on a Wall Torque

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  21. E

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  22. S

    Finding the potential energy if force depends on both position and time

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  23. T

    Finding the magnitude of the hydrostatic force per unit of circumference

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  24. Jehannum

    I Gravity: Exerting Force or Warping Spacetime?

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  25. I

    I About the repulsive force between two electrons

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  26. J

    What is the frictional force on a wheel-disk system?

    The figure is in the attached image. My attempt: I(wheel-disk system) = 0.5mr^2 + MR ^2 = 0.5(0.2kg)(0.1m)^2 + (1.5kg)(0.3m)^2 = 0.136(kg)(m^2) Fnet(of object) = Ma Mg - T = Ma T = Mg - Ma Fnet (wheel-disk system) = (M+m)a Mg- Ma - Fr = (M+m)a a = 0 because system in equilibrium Mg -...
  27. D

    Missing or mistaken door slam force formula?

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  28. FEAnalyst

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  29. T

    Understanding the Point Of Action of a Force

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  30. S

    I When is weak interaction a force?

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  31. F

    Work-KE theorem and net force....

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  32. DaTario

    I On the weak force and beta decay

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  33. Huger

    Friction coefficient and the force on a syringe plunger

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  34. CheesyPeeps

    Force on side of tank filled with liquid of variable specific weight

    Homework Statement: An open tank with a rectangular side 1 m wide and 4 m high is filled with a liquid of variable specific weight, γ, with γ = 50 + 2y (N/m3), where y is measured vertically downward from the free surface. Find the magnitude of the force on the side of the tank. Homework...
  35. T

    Understanding Units of Force (Newtons and Pascals)

    Hi all I am trying to get my head around some units of force. 1) I have units of:- Kg * m / s^2 Am I correct in thinking that these are units of Newtons. So if I had 560Kg * m / s^2, then can I say 560 Newtons - would this be correct? 2) Secondly I have units of:- kg/s^2 I have no idea...
  36. T

    Engineering Understanding Force / Pressure Equation

    Hello all I am trying to understand the pressure equation. I have the following question:- I understand this, to me what this says to me is the total force acting on the wall as a result of the water of 12m is 706320 Pascals.This is where I get a little confused, I have the following...
  37. blueboo33

    Find the force while lapping a specimen

  38. T

    I Measuring the force between air molecules

    If there was an atractive force between air molecules, how could this be measured? The force should be small. In the range of the force between watermolecules (hydrogen bond).
  39. RyanRhino

    Calculate the average force used to drag a box up a ramp

    I first wrote down that 55% = Eout/Ein I also know that W = (Facos20)(4) and I substitute it into the first equation 55% = Eout/[(Facos20)(4)] But I'm missing two variables here. Did i forget something or is the question missing some information?
  40. Carbretta

    Engineering Calculating Shear and Tensile force in a rivet at an angle

    Hi all! I have used this forum a few times and it has been very helpful, however now I am stuck. I have completed the question above however I have conflicting information regarding the Tensile and Shear force being applied to the rivet. I use the following calculation for this: Shear Force...
  41. F

    Correct understanding of the tension force

    Hello, I am reviewing the concept of tension, a force that expresses the internal tensional state in a body (rope, chain, string, solid body). My understanding is that the force of tension "derives" from the stress tensor and relates (it is the product) the diagonal tensor components to an...
  42. M

    I New force of nature discovered?

    Posted on more pseudescience related sites is a story about, a group that claim to have discovered evidence of a new force of nature, with a claimed sigma of 7,7. The arxiv paper have not yet been peer-reviewed, so I am not sure if it is allowed. If not I am sorry, and will understand. I am...
  43. kolleamm

    What force makes muscles contract?

    I know muslces have fibers and all sorts of structures but how do they actually attract themselves to each other on a very atomic level? Is it some sort fo chemical bonding force or?
  44. Kaushik

    Find the force acting per unit width on the vertical wall

    A container of height 3m and width 5m is filled with water upto 2 m. It is accelerated such that the water is at the brim (it is about to spill). When it moves with this acceleration find the force acting per unit width on the vertical wall. I found the acceleration for the condition provided...
  45. Lidor

    A force exerted on a plastic ball in a rubber tube

    Hello, How can I calculate the force that must be exerted on a ball inside a rubber tube? Thanks
  46. K

    Multi-surface Frictional force

  47. D

    How to find the magnetic field and magnetic force due to a solenoid loop

    I'm not so sure how to begin with this problem. I was thinking of usign superposition. I think that the field on the conductor due to the parallel segments of the coil is zero, since Ampere's Law tells us that the field outside the solenoid is zero, right? For the perpendicular segments, I used...
  48. E

    Calculating Masses Using Gravitational Force Equations

    F=Gm1m2/r^2 2.67 = (6.67x10^-11)(m1xm2)/25000000 M1xM2 = 1 x 10^18 M2 = 1x10^18/M1 (Equation 1) From the question stem, we know M1 + M2 = 2.5x10^9 (Equation 2) So, substituting Equation 1 into Equation 2 we get: 1x10^18/m1 + m1 = 2.5 x 10^9 I'M STUCK FROM HERE ONWARDS... in the solutions...
  49. E

    Question about gravitational force

    Hello, I hope you are all very well ! Let's say a man, standing on point "0 m" throws a ball 10 m in the air. The gravitational force goes in the opposite (down (always)) of the action (up): I supposed it's -9.81 m/s². The same action but this time the man stands on the point "10 m" and the...
  50. T

    Questions about using an Inertia Wheel to apply a compressive linear force

    Summary: How to define dimensions of an inertia wheel Firstly, I have been working in aviation industry, making me to involve in the Physics a lot. For the last few weeks, There have been a problem to solve since the manfacturer had not wanted to help us by not sharing information. We have...
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