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. I

    Why do I keep getting friction coefficient as a negative?

    I mean, I know why I am getting that result(because acceleration is negative), and I know that is wrong butI don't understand how do I get the correct answer... m=5000kg Vi=10m/s -> initial velocity Vf=0 -> final velocity t=5s mi=?I first calculated acceleration(Vf=Vi+at -> a=-10/5= -2m/s^2...
  2. Venturi365

    Find the unkown tensions and masses in the situation below

    TL;DR Summary: I don't know if my procedure is correct in this excercise I've tried to solve this problem but I find my solution unintuitive and I think I might be wrong. First of all, applying Newton's Laws I calculated the value for ##T_1## like this: $$ \begin{align} \sum F_{x} &=0\\...
  3. Tesla In Person

    I Pulley question -- Three pulleys lifting a mass...

    Hi, I have this pulley question, i have to find the force F that needs to be applied to the string to keep the system in equilibrium. I found 150N. Is it correct? T_1= 300N and T_2=150N so F is 150N.
  4. U

    I If centrifugal force doesn't exist, why does a glass move outward in the fridge door?

    If centrifugal force dont exist why glass of water moves outward/toward me when I open fridge door? Glass of water moves out in relation to door and in relation to earth, so what force push glass out?
  5. H

    I Force of an Electron on a Potential Wall?

    I've been looking at a practice test for an introductory class in quantum physics, and I've found a really weird question. It asks for an estimation of the force that an electron exerts on the walls of a box of known length during a collision. This seems like an entirely nonsense thing to ask...
  6. Mike_5158

    Calculate force required to eject a sheet metal part from a die cavity

    How do I calculate the force required to eject a sheet metal part from a die cavity. Coefficient of friction: 0.35 Surface area: 521.26 mm2 Elastic modulus: 68.9 GPa Material: 3003 Aluminium Material Thickness: 0.7mm Any help would be much appreciated. Thanks
  7. S

    I Question: Interpretation of Current and Magnetic Field Using Relativity

    The current in a wire is said to produce a magnetic field and a force on a charge. It is said that the correct way to interpret the effect is because of relativity. So does that mean that that the most basic non-relativistic equations that offer basic calculations of the forces and fields are...
  8. tellmesomething

    Centripetal force direction confusion

    So far: I an having trouble in the FBD. I drew one completely opposite to one I found on google . in this image NORmal force is pointed away from the cyclist and centripetal force is pointed away from the centre . mine was the complete opposite am i wrong?
  9. U

    I Newton's 2nd law for an object in free fall

    From inertial frame, object in free fall has just one force mg. So Fnet=non zero, but acceleration =0, isnt this in "fight" with Newton 2law? Is object accelerating or not ? Can I say, yes object is accelerating but object dont "experience" acceleration?
  10. Memo

    Moment of force, rod with mass

    OA*P_A = OH*P + OB*P_B ⇔ OA*P_A = ¾*OA*P + 2OA*P_B ⇔ 5*10 = ¾*0.4*10 + 2*P_B →P_B=23.5 →m2=2.35 (kg) My result doesn't match the answer hint, and when I change the rod's centre of mass to OH=1, it fits the answer hint. How do I determine the centre of mass in this situation?
  11. S

    Towing two stacked boxes up a ramp

    Answer is (a) F ≃ 675 (N); (b) F ≃ 859 (N) (c) v ≃ 2.2 (m/s).
  12. K

    Jackhammer on Vehicle Suspension, Unsprung Mass, Tire patch load

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  13. mazia

    Questions Regarding a Cat Going Up a Ramp

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  14. yashboi123

    Force exerted on block B by Block A when being pushed on a frictionless surface

    I was just wondering why you would do mB * a to get the force A is exerting on B instead of mA * a
  15. mazia

    Question(s) Regarding Magnitude of Force (Window Washer Problem)

    So, ignore the -0.72, I was just trying to see if I had a sign error (I then remembered magnitude is absolute value) but basically: Since the weight is 12.0N, theta is 53.1, and the coefficient of kinetic friction is 0.100, I just plugged those values into the equations above...
  16. K

    Need help calculating maximum stress in a bolted assembly

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  17. D

    I [Question] Calculating the force generated by a tarp hung between two walls

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  18. P

    Problem with when to use Force and Energy. What compresses spring/

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  19. Lotto

    What force is needed to push out this slab on the bottom of the stack?

    The picture is here: I understand that friction I need to overcome is ##5mg\mu##, but why do I need to accelerate the slab on acceleration ##g\mu##?
  20. Nova_Chr0n0

    Engineering Resultant Force and Direction using Parallelogram Law

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  21. D

    What is the Resultant Force from adding these two forces?

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  22. Ggb

    B Coulumb's Law at 1 light year distance

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  23. A

    I Calculating Force on a Golf Ball when Putting on a Level Green

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  24. Jim Robison

    B Is Time a Fundamental Force in Physics?

    We all know the four fundamental forces in physics: gravity, electromagnetism, and the strong and weak nuclear forces; and there is now some discussion about a fifth, more obscure force involving muons. But I have a question; could the fifth force be something we deal with every day? Could it...
  25. N

    I Sound pressure and inverse distance law

    Hello, I am confused as to how to think about sound pressure and the distance from a sound source. Let's assume that a sound wave is omnidirectional and propagating away from a source in a sphere. We have the following two equations: Pressure = Force/Area Intensity = Power/Area Many texts...
  26. E

    Work done by non-conservative force while particle moves in circle

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  27. S

    Determining Maximum Torque in a Truck and Forklift System

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  28. doconnor17dan

    Calculations for Hydraulic Jacks lifting a load

    This cylinder is connected by a pipe to the larger diameter jack cylinder on the right where pressure p2 acts on the piston which has an area A2 and is able to lift a load equivalent to the force F2. The piston area of the hand pump cylinder is 2.0 cm2, the piston area of the jack piston is 10.0...
  29. S

    I When Water acts like Glue (flat surfaces)

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  30. jr5

    Determine Force for inclining platform

  31. Nova_Chr0n0

    Correct approach in resolving a force into its different components

    I've already got the answer and the way to solve it (parallelogram), but I'm just wondering why I cannot use the technique I've learned in the lesson torque. Let's focus on the line AB, if I use what I've learned in torque, the components would be like this: To find the force component in...
  32. K

    Design of bolts - Influence of higher free length

    Hello all, In a recent discussion, I came across this question of influence of free length (or unthreaded length) in bolts in retaining the clamping force between the elements to be joined. Out of the two proposals in the attached pic., which one will keep the two plates clamped for a longer...
  33. Lotto

    How to calculate the wind force acting on a water drop?

    TL;DR Summary: I have a water drop falling with a constant velocity ##v##, since ##mg=\frac 12 C \rho S v^2##. Wind is blowing with a velocity ##u## only in a horizontal direction. What will be its force acting on the drop? I would use this equation ##F= \frac 12 C\rho S u^2##. When I want to...
  34. Lotto

    B How will object's velocity change when a frictional force increases?

    Let's say that the mass of the objest is suddenly bigger, so when I want to maintain the constant movement, my force must increase as well. But will the velocity have the same magnitude? I think that the velocity will be smaller, so if I want to have the same initial velocity, I must apply an...
  35. J

    B Force transition through spring

    We put object on weight ang get a mass. What would that mass be if we put a spring between object and weigt, so that the spring woul shrink to half its original size?
  36. Say17

    Calculating Tension in a System of Trolleys

    Hi all, To find out the tension. First I have to find out the a. 1. step F = ma F = (m1+m2) *a F = (1+3)*a F = 4*a F/4 = a F = 10N + 50 N F = 60 N 60/4 = 15 m/s^2 2.step T =( m1/ (m1 + m2)) * F T = (1/ 1+3) * 60 T = 15 N But the final result is 20N. Thanks for your help!
  37. Slimy0233

    I Force on Body Attached to Spring at Displacement x - A.P. French

    Source: A.P. French's Vibrations and Waves I do not recognize the first equation, can someone explain how it came to be? The reasoning behind it. How can force on a body attached to a spring at small displacement x be represented as ? I know recognize F = - kx (restoring force) I realize...
  38. sophiecentaur

    A How can a 'Principle' produce a 'Force'?

    In a collapsing star, the expression for what goes on is "degeneracy pressure". The way it's put is that the Pauli Exclusion Principle just doesn't allow more than one fermion to exist in one place (state). So the star reaches a certain volume and, on the way, produces a lot of Energy. I can...
  39. C

    Explanation for Newton II giving negative mass in my Physics lab results please

    I am trying to verify Newton II. The setup I am using is, Where ##m_1 = 0.887 kg## is a cart and ##m_2 = 0.02016 kg## is a small hanging mass. There is a force sensor on ##m_1## to measure the force acting on it from the string and the acceleration of the cart. To verify Newton's Second Law...
  40. H

    Calculation of Box's Acceleration on a Trailer with Friction

    Question picture: My solution: Where: S is the lineforce Ff is the force as a result of friction a is the resulting acceleration F is the acting force The answear is supposed to be a=(F-2mg(mu))/(m+M) Any idea what i could have missed? Thanks for your help on beforehand!
  41. Mohmmad Maaitah

    Deriving force from momentum using d(mv)/dt

    How did the d(mv)/dt become the other two? Can someone explain how do we derive for new formulas in physics?
  42. paulimerci

    Find the magnitude of the electric force from 3 charges at vertices of a cube

    There are three charges with +1 μC and −1 μC, are placed at the opposite corners of a cube with edges of length 1 cm, and the distance from P to B is 1cm 2. I labeled them as A, P, and B, which is shown in the diagram below. Since we need to find the magnitude of the charge at point P and the...
  43. G

    How to find the equilibrium position of three masses (two of them fixed)?

    Question: Suppose that two bodies of masses m1 and m2 are a fixed distance d apart, and that both of them act on a third body of mass m. Find the position of the third body such that the two forces are in equilibrium. I have solved this question and obtained the answer listed in the back of the...
  44. E

    Work done pushing a spring from the side

    My question is whether I've formed the integral for the work done correctly? It just seems a bit unwieldy to me... If I call the extension of the spring ## x ##, I can see that ## z = \frac l 2 + x ## and ## z^2 = \left( \frac {l} {2} \right)^2 + y^2 ##. Combining them gives: $$ x = \sqrt {y^2...
  45. mangofan

    I Electrostatic force exerted on an electron inside a nucleus

    This is SAMPLE PROBLEM 25-7 from "Physics" by Resnik, Halliday, and Krane, in the chapter "Electric Field and Coulomb's Law". After describing the behavior of uniformly charged spherical shells: follows a sample problem: The solution to (a) goes to say that the volume inside R/2 is 1/8 of the...
  46. ARoyC

    Total Force on a Point Charge in Motion

    As the observer is moving, there will be a magnetic force. Electric Field of the Rod = λ/2πεr r̂ Electric Force on the Point Charge = qλ/2πεr r̂ Magnetic Force on the Point Charge = q(vxB) = qvB n̂ = qv(µI/2πr) n̂ = qv(µλv/2πr) n̂ = µqλv²/2πr n̂ Total Force = Electric Force + Magnetic Force
  47. gkg

    A Force Changing With Distance (bead moving on a curved wire)

    I initially tried to solve this equation using work, but was stuck in a confusing integral that didn't make sense. I am almost sure that the utilization of energy is needed to solve this equation, but I have been flustered for the past three days at solving this.
  48. E

    Work done by a normal force (or rather, work NOT done)

    This question states that the normal force of the stairs on the woman does NO work. I do not understand how this can be. I would reason like this: The woman propels herself up the stairs using her legs. Her legs push down against the stairs, and the consequent normal force pushes upwards on her...
  49. nav888

    Work done by a force down a ramp

    The mass of the bike and person is 190kg Calculate the average accelerating force from X to Y, if the bike has a velocity of 30 at point Y. I am struggling with this question, I know that Fx = Work Done, but I also know that the only way to release GPE as KE is for gravity to do positive work on...
  50. P

    I Finding the Axis of Rotation with Given CoG and Force Point

    [Mentor Note: See post #10 below for an updated problem statement using LaTeX and with a better drawing] what i want is to find the axis of rotation when the centre of gravity and point on which external force is acting is given along with the magnitude and direction of force. In the example...
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