What is Forces: 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. greg_rack

    Solving a Problem: Forces Acting on P

    Hello guys, here's a problem which I'm having troubles solving. It asks for the forces acting on P when ##\theta=60^{\circ}##. I thought for this problem it would have been convenient to consider a polar reference system(r, theta). Drawing the FBD of pin P at a moment in time, we will have 3(?)...
  2. muna

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    Hey guys, help me out a bit here. I want to form 2d static equilibrium equations for a shopping cart. This is for an assignment. I'm kind of confused about the support reactions. I'm not sure how I should analyze the basket. I was going with A as a fixed support (see image) since I'm guessing...
  3. ergospherical

    I System, potential energy, and nonconservative forces: The whole story

    [Mentors' note: This thread was split off from https://www.physicsforums.com/threads/system-potential-energy-and-nonconservative-forces.1009237/] This is not a particularly helpful way to think about things; For a general mechanical system, you usually split the specified forces into external...
  4. Khalid Qasim

    Bernoulli’s Equation and External Forces

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  5. F

    I System, potential energy, and nonconservative forces

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  6. SpectraPhy09

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  7. I

    Slider Crank Force Analysis: Understanding the Equilibrium Forces and Results

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  8. M

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  9. H

    Forces and laws of motion -- Big gorilla hanging from two vines

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  10. N

    B Vector of forces (question about how a scale works)

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  11. A

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  12. TheBigDig

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  13. J

    I Car acceleration if resistance forces don't exist

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  14. G

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  15. Z

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  16. G

    To calculate the forces on a composite body

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  17. curiousPep

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  18. H

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  19. S

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  20. ronald_hinh

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  21. K

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  22. K

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  23. S

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  24. S

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  25. B

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  26. Zeeshan Ahmad

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  27. C

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  28. A

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  29. F

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  30. L

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  31. A

    B Projectile motion — Thinking about forces on a curve ball

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  32. Shreya

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  33. B

    A Measuring new forces with molecular vibrations

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  34. jackiepollock

    B Problems regarding electrostatic forces in everyday levitation

    Hello! I'm reading this part of the A-level physics book and finding a few places that I couldn't wrap my head around. They are underlined. 1) When saying oxygen, is it saying that oxygen is the most abundant element in the shoe atoms? 2)I am not too sure why the force per atom is shared...
  35. L

    B Inertial Frame of Ref & Forces: Understand Special Relativity

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  36. Pratyeka

    B Do Gravitational Forces Increase for Objects Moving at Light Speed?

    Since an object's apparent mass increases as it approaches the speed of light, does it's gravitational forces also increases? (From a stationary observer's point of view)
  37. M

    A Moments and forces in different frames of reference

    Good morning! I know this may sound a little odd, because there is a theorem regarding it, but i have this question. Basically, a CFD analysis gives me the value of the forces and the moments, as a function of fuselage's orientation, in a particular frame of reference. How can i calculate the...
  38. almoga

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  39. H

    I How do forces change with speed?

    Hey dear physics community :) I ask myself what exactly happens to forces between materia when the materia hits near lightspeed. I know, that for an objective bystander watching let's say elon in his rocket with 99,99999% the speed of light, that the time goes slower, the mass of the rocket...
  40. F

    Four fundamental forces of physics -- explanation for dummies please

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  41. J

    Cam forces acting on a linear motion bearing with nonlinear forces

    I have a machine I am designing that for all intensive descriptions, is a simple press designed to compress loose product into a puck like shape. The press force comes from a roller bearing mounted to a piston shaft, the rod sliding through a rigid linear bearing and the piston on the end of...
  42. T

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    Can someone please help me understand where I am going wrong. I've checked my answer many times and do not understand what I am missing
  43. Richard Spiteri

    B Exploring Buoyancy: Investigating External Forces and Neutral Buoyancy in Water

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  44. I

    Chemistry Intermolecular forces between NO particles

    The answer is dipole-dipole and London dispersion forces, but I only chose London dispersion forces. How would you determine whether there is a large or small electronegativity difference between N and O? And therefore how would you determine whether the N-O bond is polar covalent or non polar...
  45. M

    Should I consider internal forces for this hinged structure?

    Summary:: A hinged structure applied with a load, should the structure totally been calculated in order to find the resultant force? Hello, Two situations, the first is a simple structure with a 20 N load at point C. The moment-equation is composed next to it. Second situation: A hinged...
  46. M

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    Summary:: Hello all, I need help with this question, ill attach the equations i managed to solve. How do i continue from there?
  47. R

    How to interpret the center of aero forces on a sports car?

    Hello. I am working on a physics project for a simulation title and have stumbled upon on an interesting challenge. Below is the example from wind tunnel data of a Dodge Viper GTS sports car. Wheelbase: 2,44m Lift front axle: 54kg Negative lift rear axle: 26kg Can somebody please explain to...
  48. S

    Hurricane forces — Comparing the force from a 60 mph wind to a 120 mph wind

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  49. G

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  50. D

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    Summary:: Require to determine the designated forces using principle of virtual work ( unit force method ) I have no idea how to determine the multispan beam using virtual work, if I start to analyse the subsidiary portion BC member, the Yc can be calculated and following by the Ma... it seems...
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