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. A

    Calculate the minimum force required

    I tried taking the components but got stuck there on what value of theta I should take
  2. G

    Analysis of a Figure to Calculate Force and Moment

    Figure: My attempt at a Solution: $$\overrightarrow{TFD}=TFD\dfrac{(-0,16\widehat{i}+0,11\widehat{j}-0,08\widehat{k})}{0,21}$$ View from above: We calculate ##D##: $$\sigma =90-\arctan \left( \dfrac{0,07}{0,240}\right)=73,74\, \textrm{º}$$ $$d=0,16\cdot \sin (\sigma)=0,1536\, \textrm{m}$$...
  3. samy4408

    I I found 2 formulas about surface tension -- which one is correct?

  4. G

    Tainter Damper Figure: Analyzing Forces

    Figure: Attempt at a solution: $$b=12\, \textrm{m},\quad H=8\, \textrm{m}$$ a) $$F_H=p_{CG}A=3767040\, \textrm{N}=\boxed{3767,04\, \textrm{kN}}$$ $$A=8\cdot 12=96\, \textrm{m}^2$$ $$p_{CG}=\rho_g h_{cg}=39240\, \textrm{Pa}$$ b) $$F_V=mg=\rho_g V$$ We calculate ##\theta \rightarrow 8=10\cdot...
  5. A

    Calculating Energy Dissipation for a Moving Object Using Integral Calculus

    Since ##F = -b * v## I said ## F(x) = -b*v(x) ## Also x(0) = 0 and x(T) = ## \frac{1}{3}aT^3 ## I made the integral ## ΔE = -b* \int\limits_0^\frac{aT^3}{3} v(x) dx ## I wanted to replace v(x) with v(t) somehow I first tried ##v(x) = ax^2## but then realized that was wrong Then I tried using...
  6. G

    Total force that a fluid exerts on a cylinder

    Figure: I have calculated the density of the cylinder: ##5479,0\, \textrm{kg}/\textrm{m}^3##. Attempt at a Solution: $$d=0,12,\,\, L=1,1,\,\, D=0,122,\,\, e=0,002,\,\, c=0,02,\,\, b=0,4,\,\, a=0,7$$ $$\omega =100\, \textrm{rpm}=10,472\, \textrm{rad}/\textrm{s}\quad e=0,122-0,12=0,002$$ We...
  7. J

    Hollowed out sphere exerting gravitational force

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  8. G

    Resultant force and centre of pressure in a tank

    Figure: a) CASE A ##\rightarrow p_a=101300\, \textrm{Pa}## $$F_{\textrm{res}}?,\,\, y_c-y_{cg}=y_{cp}$$ We find ##h_{cg}\rightarrow h_{cg}=3+h## $$h=0,75\cdot \sin (30)=0,375\, \textrm{m}\rightarrow h_{cg}=3,375\, \textrm{m}$$ $$p_{cG}=\rho_{H2O}gh_{cg}=33108,75\, \textrm{Pa}$$ We calculate...
  9. S

    Tetrahedron with 3 points fixed, and force applied to 4th

    My approach to this problem is to recognize that the tetrahedron being still means that net torque is zero and net force is zero. Fd is given Fa + Fb + Fc = -Fd Fa X a + Fb X b + Fc X c = <0,0,0> This can be split up into a series of 6 equations, 2 for each component. However, this is where I...
  10. FEAnalyst

    Gear teeth force from the rotation angle

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  11. dextercioby

    I Extending Newton's laws -- Is the concept of force still defined?

    It is argued that the correct interpretation of Newton's 2nd Law for one body of mass ##m## reads "The dynamics (i.e. vector sum of all external forces acting on the body = "all its interactions") dictates the kinetics (i.e. time derivative of the momentum vector = "motion")", under the...
  12. Crunge

    The maximal normal force (Friction with slanted surface)

    The problem that I immediately ran into was how I would calculate N without knowing Fmax. I didn't think the y-component of N would simply be the same magnitude as mg. After being stuck for a good while I even tested if it was, by dividing the magnitude of mg with cosθ, which of course ended up...
  13. Idontknowhatimdoing

    Normal force at the top of a vertical loop -- Circular Motion Dynamics

    From the equation for centripetal force, I can see that the centripetal force is proportional to v^2. Does this have something to do with why there is a normal force at the top? Does the velocity of the object require there to be a normal force? If so, why is that the case?
  14. S

    How to find minimum possible mass

    Unfortunately, this is not the right answer.
  15. Elementard

    Force of spring equation problems

    m=6.00Kg K=145N/m a=1.80m/s Fp=Fs ma=-kx (6)(1.8)=-(145)x x=-0.0745m I’m just wondering why I see some people make Fs=kx instead of -kx? isn’t the force of a spring a vector?
  16. P

    Rolling mill force calculations

    Hi, I'm building a rolling mill for flattening out bits of steel and I'm trying to make sure it's not going to break. I know that with a 1500w motor geared down to 60rpm (2pi rad/s) i end up with 239Nm of torque. 239Nm working at a radius of 0.0375m gives 6369N of force generated at the edge...
  17. theanswer2physicsisu

    Force and Kinematics -- Accelerating a 10kg box vertically

    I realize that there is a downward force of gravity weighing the object toward earth’s surface, equaling F = mg (downward). The upward force would have to be something at least as much as the downward force in order to lift the object up ”such that it is accelerated from rest to a velocity of 5...
  18. K

    I Understanding Three Force: Definition and Application

    We define four force as one which satisfies : ##\mathbf{f}=m \mathbf{a}## where ##\mathbf{a}=\frac{d \mathbf{u}}{d \tau}##. The quantities in bold face are four vectors. Hartle pg 88 defines a three force as : ##\frac{d \vec{p}}{d t} \equiv \vec{F}## Where ##\vec{p}=\frac{m...
  19. F

    I Reaction force of and its relation to normal force and friction

    Hello, When we consider a block sitting on a surface, the gravitational force ##W## and the normal force ##F_N## are applied to the block. Both equal i magnitude and opposite in direction. We call the normal force the reaction force exerted by the surface on the block. Now we consider the...
  20. F

    I Distributed Forces and force density....

    Hello, Forces can be concentrated (when acting at a single point) or distributed (when acting over a surface or line). In the case of distributed forces, we can find the resultant concentrated force by calculating a surface or line integral of the force density ##f(x)## w.r.t. an area or length...
  21. M

    Calculating the force that a permanent magnet exerts on a particle

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  22. jaumzaum

    I Does the electrical force also respect the Kepler Laws?

    I was wondering if the electrical force, which is a radial force that depends on the inverse of the distance squared, also respect the Three Kepler Laws? If so, what will the constant for the third law be?
  23. Th3

    B What’s the necessity of the strong force?

    To put it simply: Why do we have the strong force? If the goal of the fundamental forces (in a heavily generalized sense) is to bring particles to a lower state of energy, how is the strong force participating to this? Could it be due to atoms being a very stable configuration? If this is the...
  24. S

    B Can gravitational force have influence on objects at infinitely long distances?

    Can gravitational force have influence at objects at infinitely long distance? Is gravitational force in the form quantum packets?
  25. babaliaris

    I Pendulum Tension Force -- How to calculate the full vector?

    Hello! I'm trying to understand how this pendulum works. I found this video that explains how to calculate the T force from the rope. He uses the preservation of kinetic and potential energy in order to find the magnitude of the velocity and then using Newton's second law, he calculates the T...
  26. N

    I Exploring Magnetic Force: Magnet vs. Wires

    I understand the iron fillings become little magnets all pointing in the same north south direction similar to the spin aligned electrons in the permanent magnet. Similarly, a compass near a wire traces out the magnetic field lines ie North/South. My question is how do I reconcile the fact that...
  27. Z

    How to solve for face pressure on Roller 3 using the force pushing 1

  28. josephsanders

    I Tangential electric force at a surface

    Suppose you have an infinite plane of charge. If the surface charge density is uniform, would the tangential electric force always be zero, even if it is not a conductor nor static? My thought process for this is that if you look at each point charge and draw the electric field lines, then at...
  29. J

    Lorentz Force In Capacitors

    I am searching online for resources regarding studies done on the effect of the Lorentz force due to short circuit faults in capacitors. Although a DC-link capacitor only sees the ripple, there would be high current during a fault. Since F=(qE + JxB), I am curious what the effects of the high...
  30. W

    Tilting a 55 Gal Plastic Drum: Calculating Force Needed

    I have been tasked with tilting a plastic 55 gallon drum that contains lube to an angle of about 20 degrees. I would like to use pneumatic cylinders as air is readily available here. The plastic barrel has a 23.5 inch diameter and is 35 inches tall. The barrel and contents weighs 450 pounds...
  31. Ahmed1029

    I Is electromotive force always equal to potential difference?

    In the case motional emf, there is a static magnetic field and a rectulgular loop that goes into the field region, then current is produced. There is no electric field, but there is an emf. However, Griffiths states that emf is equal to the potential difference between the source endpoints. But...
  32. E

    B Normal Force Discrepancy for Wedge Vs. Ramp

    I have seen a few posts on this subject before, but none have really answered my question. For clarity, I will refer to the 1st example as a wedge, and the second as a ramp (although both are of course inclined planes). With both examples that I outline below, we will assume no friction, and a...
  33. Ahmed1029

    I Wave number, frequency, and velocity in dispersive waves

    1) If I generate a dispersive wave, will it have well-defined constant wave number and frequency? Ones that don't change in time? 2) does the velocity of any point on the wave stay constant in time? 3) How does force interact with waves? Does a free wave act in analogy with free particles...
  34. N

    Convert moment force at lever support

    I am trying to determine if a clamp holding a lever with a mass at one end can experience zero or reduced torque either by balancing the forces or converting the rotational torque into another form such as linear, I’ve looked at counterbalance with Steadicams etc. but I believe this just...
  35. R

    Engineering Dynamics Problem with a Driving Force, 2 Wheels, a Spring and a Damper

  36. T

    I What is the difference between the resistance force and the friction coefficient?

    Hi I have been wondering what is the difference between resistance force and friction coefficient. While doing research online I could not find a clear answer. Maybe someone here will now:bow:
  37. old fart

    Calculating Force Needed to Raise Steel Tower

    How did you find PF?: looking for simple formula to calculate force needed to raise steel tower. I am not on social media and have no idea how to use a forum. at almost 80, I find having to hand crank a ham radio tower up and down to be challenging. I must lay it down to work on the antennas...
  38. T

    How Is Cylinder Force Calculated to Rotate a Beam with a Horizontal Load?

    I am trying to calculate the force required to lift/move the beam clockwise from the shown position. I have a force (F1) acting at the end of the beam, 5,000lbs pushing to the left, as shown. What is "Fcyl", or the force required by the cylinder to life the beam with the acting load, and rotate...
  39. Differentiate it

    Friction causes a torque - then why do we sum it as a regular force?

  40. Jorrie

    A Cosmic Tidal Force: Measuring CTF With Strain Gauge

    In order to make it as simple and non-controversial as possible, I propose a setup where inhomogeneity and change of reference frames play as little role as possible, i.e. in free space and with its center of mass comoving. I'll call that point the origin and set up my lab there. Rockets...
  41. mopit_011

    B Equivalence of Frictional and Applied Force

    The following passage is from Halliday Resnick Krane in Chapter 3 which is about dynamics in one dimension. "We can measure frictional forces. By placing the body on a horizontal surface where it experiences a frictional force, we could attach a spring and pull the body with just the right...
  42. U

    A The force from the energy gradient

    From this post-gradient energy in classical field theory, one identifies the term ##E\equiv\frac{1}{2}\left(\partial_x\phi\right)^2## as the gradient energy which can be interpreted as elastic potential energy. Can one then say that $$F\equiv -\frac{\partial...
  43. MrSimp

    B Does Force Travel Faster Than Light?

    Imagine a plane 1 light minute across. Now imagine 1 person on either and of that plane. Between them, is a thin indestructible bar that is 1 light minute in length. In the center of this plane, a simple device has a wire that leads to a motion sensor on the left side of the bar. If the left...
  44. C

    I Is there traction force between moving electrons & copper wire?

    Common sense: walking on road, there is traction between shoes & earth. I'm wondering: same thing for electric current's electrons & copper wire?
  45. AK93

    Required force to hold or pull inclined object downwards.

    Can somebody help me to solve this problem and guide? I need to calculate minimum force (F) (Newtons or kilograms) is required to pull down object (K1) to (K2), or to hold it in position. Angle between (K1) and (K2) = 50 degrees. Using mounting points (P1) and (P2). (K1) mass = 3.5 ton, (A)...
  46. Rikudo

    Fictitious force in a binary stars

    I have a difficulty in understanding the question. Fictitious force is a force whose motion is described using a non-inertial frame of reference. Which frame is the question referring to?
  47. G

    Find the Upward Force of a Boat with 6 People Aboard

    Apply Principle of Archimedes - upward force is equal to the weight of the volume of water displaced. Density (boat) = 120 kg/(3x1x.24)m(3) = 500/3 kg/m(3) Density of water = 1000kg/m(3). Density (water)/Density of boat = 1000 kg/m(3)/(500/3) kg/m(3) = 6. So density of water is 6 times the...
  48. MatinSAR

    Question about Elastic force and Buoyancy force

    Suppose a wooden cube with a side of 10 cm is connected to the bottom of a water container by a spring. If the density of wood is 0.6g/cm^3 and the density of water is 1g/cm^3 , what is the elastic force of the spring? Is it 4N or 6N ? I think the answer is 4N … But the book says it is 6N ...
  49. D

    Resultant pedal force (FRESULTANT) Force tangential to the crank arm

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  50. E

    B Pressure through a curved hose - expected results?

    Hello, I am doing some quick experiments testing how pressurized air behaves when being ejected from a straight vs. curved object, and I am wondering if this is the expected behavior and a possibly quick explanation of why this would be behaving this way... I am using the model below and...
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