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. Prabs3257

    Electrostatic force equilibrium

    I was thinking that we can equate the electrostatic potential energy and the spring energy (as the force is similar to that of a spring so energy will also be 1/2kx^2 ) but i am not getting the correct ans but by equating the net force on one charge to kr i am getting the correct ans can...
  2. Prabs3257

    Is Equating Energies a Better Solution for Finding Extension Under Spring Force?

    Its a very basic problem and my friend suggested a solution that we should equate mg and kx ie mg=kx and just plug in m=8 and x=0.16 but i think that we should equate the energies like mgx=1/2kx^2 ie because at the point where mg will be equal to kx the mass will still have a velocity hence it...
  3. T

    Understanding Shear Force: How to Calculate and Interpret Shear Force Diagrams

    Hello all I was hoping some could shed some light on the idea of shear force on members. I have the following simply supported beam:- Considering only the left of the beam to just to the right of F1; my gut instinct would be to say that the shear force or failure is greatest at the...
  4. kraub

    What is the required piston force for a crane boom with specific dimensions?

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  5. jackattack825

    Normal force between stacked boxes

    Σ F= -F(gravity from earth) + F(normal from earth) -F(normal from top box) +F(normal from bottom box) = (2+5) * 2.5 The forces from gravity and it's normal force cancel out, leaving us with the normal forces from the boxes. F(net of normal from boxes) = (2+5) * 2.5 = 17.5N
  6. V

    Calculating the normal force due to moment load on a thrust bearing

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  7. T

    How can the force of impact be reduced in an egg toss game?

    So I am trying to answer a question which is about an egg toss game where two people try to throw an egg at each other without breaking it.The question is how can the force of impact be reduced so that the egg doesn't break. With respect to the F = Δ p / Δ t formula, I think increasing time of...
  8. chezholmes

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  9. Alexandra Fabiello

    Force Calculation: Incorrect Result

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  10. MacGyver Megh

    B The electromagnetic force of quarks

    If an up quark has 2/3 of positive charge and down quark has 1/3 of negative charge then why don't they add together by their electromagnetic force?
  11. Fran

    Calculate the maximum force on a wheel passing over an obstacle?

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  12. F

    I Is force a a bound vector or a free vector?

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  13. S

    Arrow strike, Avg force, Conservation of energy

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  14. M

    How to Measure Impact Force / Energy Absorption

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  15. Prabs3257

    Kinetic energy as a function of time

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  16. E

    How can a reaction force do work on someone who is jumping?

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  17. T

    How To Calculate The Force Of Water Exerted On A Full Tank

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  18. D

    Is the Equation F=2+4v Dimensionally Correct for Calculating Force?

    My teacher never actually taught us how to do this problem, so I have zero idea what to do.
  19. Like Tony Stark

    Finding the constant of this retarding force

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  20. C

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  21. E

    Does the spring force do work on the spring itself?

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  22. S

    Force on a sphere due to a conducting plate

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  23. Physics4Eva

    B Is Normal Force a Contact Force Despite Atomic Repulsion?

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  24. MrDickinson

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  25. S

    Speeding bullet, average force by post on bullet

    used a) change in momentum / time, time from from kinematics equation d = vi+vf/2 *t ... 0.1 = 300*t =3.33*10^-4 then 600/0.00333 = 1.8*10 ^5 how to proceed?
  26. Like Tony Stark

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  27. I

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  28. cs44167

    How much force do I exert on the Earth?

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  29. brsclownC

    What is the magnitude of resultant force on a car on a banked curve?

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  30. MrDickinson

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  31. brotherbobby

    External force on three blocks stacked

    The figure is shown above. In order to facilitate solution, I need to separate each block and draw the free-body diagram (FBD) with all the forces acting on it. 1. Let me start with the lowest block. Let me put its FBD as shown below. For forces in the vertical direction, ##N_3 = N_2 + m_3 g...
  32. Like Tony Stark

    Understanding Pseudo-Forces in Non-Inertial Frames

    I know that, if my ##X## axis is aligned with the arm, there is friction pointing to ##O## and the ##x## component of the weight. Then, on the ##Y## axis, there is the normal force and the ##y## component of the weight. Supposing that I am situated on the arm (non inertial frame), where is the...
  33. M

    Calculating Shear Force between a Moving Film and a Cylinder

    If I have a catheter covered in a thin sheathe (think a cylinder, covered by a thin plastic film), how should I go about calculating the shear force it takes to unsheathe the catheter from the sheath (no torque here, just the catheter moving in and out)? I've thought about strain gauges (but...
  34. M

    Calculating the torque of the Laplace force on this coil

    We first determine the Laplace force for each value ##\alpha##. $$F_{\alpha} = 5(0.3)(0.4)\sin(\alpha) = 0.6\sin(\alpha) \ \text{N}$$ We then calculate the torque at angle ##\alpha##. $$\tau_{\alpha} = \frac{a}{2} F_{\alpha} = 2.5 F_{\alpha} \ \text{N.m}$$ Then we just plug in ##\alpha## and...
  35. J

    B Exploring Force & Potential Energy of a Donut-Shaped Planet

    So, let's say you have a donut - shaped planet, so a second object can move right on top of the center of mass of the first object. Does force go to infinity? How about potential energy? Or, just take one object, divide it into elements, what happens to the central element of mass within the...
  36. S

    Correct statement about gravitational force, field and potential

    I think choice B is correct because when I draw the free body diagram of each object, there are three forces acting on each of them and the resultant force is towards the center. Choice C is wrong because the net field at center is zero. I think choice D is also correct because if the...
  37. K

    What is the normal force in A and B?

    A welded square frame consisting of four equal rods each with mass m and length 2l can move in the vertical plane by means of two small wheels in A and B that move without friction along a horizontal and vertical track, respectively. The disc is released from rest in a position where the sides...
  38. A

    Find the attractive force of gravity between two objects

    Homework Statement: Henry Cavendish succeeded in measuring the value of the constant "G" way back in the late 1700s. His method was to put two known masses at a known distance and measure the attractive force between them; then he could use Newton's Law of Universal Gravitation to find "G"...
  39. NathanRB

    Which force acts perpendicular to the side faces of an axe head?

    Say that these pictures are accurate. Personally, I think I can solve this problem, but the issue is, that I had a debate on it with my Physics teacher. This is how my teacher would solve it; my teacher says that each Fk on each side is constructed from half of F and Fx. So, F = 2 * Fk * sin...
  40. Like Tony Stark

    Find the force needed for a body on an inclined plane to be static?

    Here, I have two doubts 1) if the surfaces are frictionless, then there's no force being applied on the ##x' axis## of ##m_1## except from the weight, so it should be sliding, shouldn't it? So, there's no force that I could apply to ##m_2## to keep ##m_1## in equilibrium since any force that I...
  41. S

    Coriolis force caused by tangential velocity

    From another recent thread I learned that you see a Coriolis force if an object in a rotating reference frame moves along a tangent at some velocity v. (I was already familiar with the case where the velocity is radial). I still find it a little counter-intuitive that the force has the same...
  42. M

    Object movement under the infuence of Forces on the x,y axes

    Which could be the first step to find the V(t) ?
  43. E

    The force required to move an object (piano)

  44. Y

    Breaking down cellulose using impact force

    Generic biomass such as leaves contain a large amount of total carbohydrates, mostly in the form of cellulose. Some animals such as apes and can digest cellulose and that is how they can survive on leaves. Humans cannot digest cellulose because we lack the enzymes necessary to decompose...
  45. Newby

    Calculate the quadriceps muscle force

    Hi guys, I'm new here. So I have this biomechanics module which is completely out of my league (it's compulsory but it's not what I want to do). Could someone help with the following? It's about static and dynamic loads calculation. Calculate the quadriceps muscle force applied through the...
  46. C

    What type of diagram should be drawn when applying Newton's second law?

    Honestly I have no idea how to solve this. Can anyone help?
  47. E

    Work done by a tangential force shouldn't be zero

    Applying the dot product to the position vector and force vectors yields the result that the force vector is always at 90 degrees to the position vector, namely that it is directed tangentially. The mark scheme gives the work done as 0, however I don't agree. I believe they got this by finding...
  48. S

    Gravitation (planetary motion)

    Homework Statement: The particle is moving in circular orbit such a way that the net force (F) is always towards the point p (point p is on the circumference of circle). Find the variation of force F with respect to r. i.e find the value of n in the expression F=kr^n Homework Equations: F=kr^n...
  49. T

    Calculating the number of electrons given the force of repulsion

    Homework Statement: Two small spheres spaced 20.0 cm apart have equal charge. How many excess electrons must be present on each sphere if the magnitude of the force of repulsion between them is 3.33×10^−21N? Homework Equations: Charge of an electron e=-1.6X10^-19 C F=kq/(r^2) For this I set...
  50. Universeer

    Lorentz force between two moving charges

    Two charges are moving mutually perpendicular to each other in space with constant velocities. The moment one charge crosses over the line of path of second charge the force on 1st charge (located just behind the 2nd charge moving away from it) appear to be zero (Magnetic field due to 2nd...
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