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. IMadeYouReadThis

    I Best way to create artificial forces

    First of all hello everyone, I'm a recent graduate and now I am a mechanical engineer (WEEEEE) and wanted to embark in a project that involves creating artificial forces (Newton's third law kind of forces). The project basically must have something to counter forces exercised by a hand, i.e. if...
  2. C

    Having trouble calculating reaction forces for this truss.

    Homework Statement Calculate reaction forces for truss. Truss is attached in picture. Homework Equations ΣFx=o ΣFy=0 ΣM about reaction point=0 The Attempt at a Solution attached in picture
  3. S

    Why do conservative forces MUST depend on the position?

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  4. Evangeline101

    Forces 2 dimensions: How far have the tugboats moved the log

    Homework Statement Two tugboats are pulling on a large log, as shown in the following diagram. The log has a mass of 250 kg and is initially at rest. How far have the tugboats moved the log after 10 s? Homework Equations c2 = a2 + b2 - 2abcosC c = (a2 + b2- 2abcosC)1/2 The Attempt at a...
  5. T

    Block Placed on Top of Another Block - Finding Max Force

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  6. F

    I Sum of internal forces equals zero

    This is probably a very trivial question, but my brain isn't "playing ball" today so I'm hoping someone can help me with this. Suppose I have a system of ##N## mutually interacting particles, then the force on the ##i##-th particle due to the other ##N-1## particles is given by...
  7. physea

    I How does the Capstan Law Determine T1 and T2 When the Capstan is Rotating?

    Hello! Capstan law is T2=T1e^μθ. I have problem identifying T1 and T2 in various situations: 1) when the capstan is not rotating 2) when the capstan is rotating how can I identify which side is T1 and which T2? thanks!
  8. Biker

    B Normal Force: Questioning the Physics Behind It

    In the past I used to understand it in some kind of way. But it doesn't make a lot of sense sometimes. In high school, we usually take examples where the object is placed in an incline and the Normal force is equal to mg cos theta where theta is the angle of the incline. It should equal to that...
  9. E

    Pseudo forces and negative acceleration

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  10. M

    Forces appearing on the pipe when a fluid flows in it

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  11. G

    B Quantum Model of Contact Forces

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  12. J

    How to find the forces acting on the pivot point ?

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  13. L

    Newtonian mechanics; word problem; calculate forces

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  14. C

    B How can we tell that "fictitious forces" are not real?

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  15. V

    Understanding Forces on a Toppling Bicycle Wheel

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  16. ramzerimar

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  17. E

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  18. E

    B Elevator action-reaction pair/normal forces

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  19. B

    Force Direction: Understanding Upward Motion on Lowering Objects

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  20. nso09

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  21. E

    Name of the forces caused while driving a car

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  22. S

    Forces that cause acceleration due to conservation laws

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  23. B

    What forces causes the top book to accelerate horizontally?

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  24. komarxian

    Calculating Electrical Force on Alpha Particle Near Gold Nucleus

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  25. K

    I Simple Fulcrum Force Calculation Question

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  26. Blockade

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  27. Blockade

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  28. Blockade

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  29. Blockade

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  30. Blockade

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  31. S

    Double pulley Atwood machine (with 3 masses)

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  32. Z

    Forces - Concerning Spindles with Out of Balance Loads/Help

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  33. B

    How Do You Calculate Tension in a Rope Pulling a Box with Friction and an Angle?

    1. Homework Statement You are pulling a 39kg box on a level floor by a rope attached to the box. The rope makes an angle of 21 degrees with the horizontal. The coefficient of kinetic frictions between the box and the floor is 0.23. Calculate the magnitude of the tension in the rope needed to...
  34. S

    Rotational work and forces like static friction and tension

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  35. S

    Why do conservative forces try to reduce potential energy?

    I do not understand the reason why a conservative force always "tries" to reduce the potential energy of a system at its minimum (forgive me if I said it in a wrong way). The explanation I gave me is: since for a conservative force, from the definition of potential energy, W=-\Delta U that...
  36. faradayscat

    Bridge Forces: Identifying Compression vs Tension | Homework Help

    Homework Statement How would you determine whether a member is in compression or tension given the bridge with external forces below? Homework Equations None.The Attempt at a Solution I don't need help finding the forces, I need help in figuring out compression/tension. [/B]
  37. I

    Dynamics Skier on a Slope Problem

    Homework Statement A skier on a slope inclined at 4.7 degrees to the horizontal pushes on ski poles and starts down the slope. The initial speed is 2.7 m/s. The coefficient of kinetic friction between skis and snow is 0.11. Determine how far the skier will slide before coming to rest. Answer...
  38. I

    What are the forces acting on a child pulling a wagon up an inclined hill?

    Homework Statement A child is pulling a wagon of mass 7.38 kg up a hill inclined at an angle of 14.3 degrees to the horizontal. The child applies a force parallel to the hill. The acceleration of the wagon is 6.45 cm/s^2 up the hill. Friction is negligible. Determine the magnitude of (a) the...
  39. E

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  40. Jonski

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  41. S

    Rubber on a rotating disk (angular velocity, forces)

    Homework Statement We place a rubber on the edge of a rotating disk. What forces act on the rubber? At what angular velocity, why and in what direction will the rubber fly off the disk? Homework Equations http://images.tutorvista.com/cms/formulaimages/83/angular-speed-formula111.PNG The...
  42. P

    Trajectories, equation of motion and forces....

    Setting a cartesian system how can i get the equation of the trajectory of an object knowing the forces acting on that object? Example: If F= GMm/r^2 and let be the sun at the center (point (0,0,0)) of the cartesian system how do i get the equation of an ellipse in this system? ( x^2/a^2 +...
  43. G

    For 2) wouldn't there also be an equal and opposite force on block B by block A?

    Three blocks, each of mass 13 kg are on a frictionless table. A hand pushes on the left most box (A) such that the three boxes accelerate in the positive horizontal direction as shown at a rate of a = 1.4 m/s2. 1)What is the magnitude of the force on block A from the hand? 2)What is the net...
  44. Biker

    B Rocket Hovering Equation: A Balance of Forces

    I was just scrambling and thought of rockets. So I came up with an equation for (hovering). Note: This might be totally wrong. Okay so we have a rocket with fuel with a mass of M. There is gravity acting on it so I need a force to balance things out. F - Mg = 0 F = Mg What I have learned is...
  45. KarminValso1724

    B Why do the 4 forces have the strength that they do?

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  46. Maka42

    Velocity change due to load dropped vertically onto trolley

    A trolley is moving at a constant speed down a track, with no net force acting upon it. A heavy load is dropped vertically on top of the moving trolley. What happens to the trolley's speed? a) It stays the same, b) It decreases, c) It becomes zero, d) It is impossible to say, e) It increases...
  47. B

    Calculating Launcher Mass from Projectile Acceleration

    Homework Statement A projectile launcher fires a projectile horizontally from a platform which rests on a flat, icy, frictionless surface. Just after the projectile is fired and while it is moving through the launcher, the projectile has an accelleration of 25m/s^2. At the same time, the...
  48. B

    Force magnitude and direction Problems

    Homework Statement When doing force problems, you're sometimes asked to solve for the magnitude and direction of a given force acting on an object given the mass of the object, its accelleration, and the other forces acting on it. However, the force that you need to solve for could be...
  49. L

    Force required to pull a curtain out/in?

    Hi there, I am currently trying to work out what force I will need to pull the curtain out and in (in the system shown in the attached illustration) so that I can calculate the torque required to turn the black cylinder component and therefore find out what motor I will need. I am simply...
  50. alexandria

    Forces - calculating the net force

    Homework Statement Homework Equations The Attempt at a Solution c = ([32.0 N ]^2 + [38.0 N]^2 - 2 (32.0 N)(38.0 N) cos70° ) 1/2 c = 40.5 N (is this correct?) SinA / 38.0 N = Sin110° /40.5 N (im unsure how to solve this part) A = ?? net force = 40.5 N (East ? North) I am very confused...
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