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. R

    Work Done By a Spring's Restoring Force

    Hello all. Right now I am taking physics 1 and were doing the Work-Kinetic Energy Chapter. I was just reading the derivation for the work done by a spring's force. I understand how to get the result but what i don't understand what to make of it. I understand that because a spring's force...
  2. M

    Force between two neodymium permanent magnets

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  3. S

    I Calculating force when landing on a beam

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  4. H

    Question on pulleys force and rope pulling

    I have a question about the following 33 and 34. For number 33 I think the answer is B because you have to life up against the force of gravity. While with A you have gravity helping you out. The correct answer is A but I am not sure how. for 34 I think B because you have an extra pulley so...
  5. E

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  6. naushaan

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  7. R

    Maximizing Repulsive Force with an Electromagnet

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  8. K

    Is non-linear Tension Force possible?

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  9. J

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  10. K

    I Horizontal Tension Force equation

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  11. SpaceThoughts

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  12. jamiebean

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  13. jamiebean

    What is the contact force for a 20kg object with an acceleration of 2.7?

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  14. Haorong Wu

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  15. R

    Force acting on the contact area?

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  16. coldadler

    How can I calculate the reaction forces of a torsion spring on a wall?

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  17. R

    Spring force after fixating with limited stiffness

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  18. MustafaTekinay

    How much force does a moving car exert on to the road?

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  19. brotherbobby

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  20. M

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  21. Bengineer

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  22. K

    I Nuclear Force Behavior: Confusing Isospin Dependence

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  23. archaic

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  24. V

    Tension forces of two wires in comparison to the gravitational force

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  25. chriscarson

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  26. chriscarson

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  27. Leo Liu

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    If a block slides down an inclined surface under the presence of the kinetic friction, does that mean the total energy lost by the block is equal to the work done by the kinetic friction? Thanks in advance.
  28. T

    How to calculate jump height from the force and a person's weight

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  29. H

    B Blunt force vs cutting force in penetration

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  30. JPakt

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  31. Zouatine

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  32. S

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  33. F

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  34. Like Tony Stark

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  35. r-swald

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  36. K

    Buoyant force and a water column

    Recently I viewed the Searaser video at After watching it, I feel the numbers given in the video could be wrong but not sure. So I'd like to know how I can calculate the amount of water pushed by the Searaser device at some height in one wave shot e.g. at 100 ft, 200 ft and 300 ft above sea...
  37. jisbon

    Dealing with magnetic force into the page?

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  38. K

    I What is being plotted in the nuclear potential formula by Samuel Wong?

    Hello! In Nuclear Physics, Second Edition, by Samuel Wong he shows a plot of the nuclear potential (see attached) but he also gives a formula (also attached) for the most general way of writing the nuclear potential. In that formula, we have the coefficients depending on r only, but the overall...
  39. Amik

    Spring force question with a mass suspended on a spring

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  40. SchroedingersLion

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    Greetings, I am struggling with an exercise to the Langevin equation. Suppose we are given the following differential equation for a particle's 1D time-dependent momentum ##p(t)##: $$\text{d}p = -\gamma p \text{d}t + F(r)\text{d}t + \sqrt{C\gamma}\text{d}W $$ with a constant ##C##, a...
  41. E

    How can I calculate the tension force?

    This is my attemp of solution: Since the formula to calculate the tension is T=mg I first calcualted the weight of the bridge with the ecuation W= mg m=W/g m= 18,000 N / 9.81 m/s m= 1834 kg So T=(1834)(9.81)= 17,991 N But this seems no logical to me because the Tension force is a bit less...
  42. Like Tony Stark

    Reaction force acting on a rod

    Hi, I have a doubt about reaction forces... I've attached a picture that shows two similar situations. The first one shows a rod left with an angle ##\beta## while it is on a smooth surface. The second one shows a rod leaning on a smooth surface and wall. My question is: why is the reaction...
  43. ari-anne

    Finding distance from velocity, force, momentum, mass, and time

    I solved a and b fine, I just don't know where to start c a) i=Ft i=change in p and p=mv so i=90=45v so v=2m/s b) same thing just using the other mass i=90=70v so v=1.3m/s c) v=d/t so 1.3=d/1.5 but that would be d=1.95 and the answer key says d=.96m
  44. synMehdi

    Understanding Unbalance Force in Rotating Systems

    I would like to undertand more the force caused by unbalance in a rotor, assume that the bearing is represented with 2 springs like above: The geometrical center of the rotor ##O## is equivalent to it center of gravity ##C_g## and the center of the stator (bearing) ##O'## The rotor is perfectly...
  45. J

    Canonical ensemble and Force on the Walls of a box

    Hi everyone, this is my first message after presentation so please be merciful if the notation is somewhat messy. Here's my attempt at a solution: As for points 1) and 2) I used the definition of partition function $$Z = \frac{1}{h^{3N}} \int e^{-\beta \mathcal{H}} d^3p d^3q$$ and the fact that...
  46. K

    How to Calculate the Force Required to Lift an Arm

    Hi, Hope one of you might be able to help me with some calculations :) I'm trying to calculate the amount of force required to lift an arm, based on weight, distances and angles. I made a sketch to illustrate my problem. where: Lac = Length of arm Lab = Distance from "anker-point" to...
  47. Julius Ceasar

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    This is a puzzle to me, time dilation seems to be stating two different times can exist (at least), i am asking if this is the case not demanding it is so, please help. I do not have a science background so i will be listening closely to what those that do, have to say. Momenta Similar to the...
  48. R

    Can the Normal Force Produce a Torque on an Object on an Incline?

    Hi everyone I can't understand how normal force produce torque isn't normal force acts normally on the plane so the perpendicular distance in case if it was like block will be zero, so normal force doesn't produce torque. "case of box"
  49. B

    Analyse the cutting force of this bolt cutter

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  50. S

    Find the force so that all blocks are at rest with respect to each other

    Free body diagram one each object: Block 1: Normal force upwards, weight downwards, tension to the right, friction to the left Block 2: Normal force to the right, tension upwards, weight downwards, friction upwards Cart: Contact force with block 1 downwards, contact force with block 2 to the...
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