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. Ruda975

    I Lift Force of a Rotating Sphere in the Air

    Hello, I would like to ask one question. What is the equation for the lift force of a rotating sphere when flying through the air: m = 0.25 g v = 130 m/s angular velocity = 105 rad/s radius = 3 mm air density = 1.2292 kg/m^3 air pressure = 101200 Pa air temperature = 15 °C = 288.15 K If anyone...
  2. J

    Velocity, traveling distance and friction force on a sliding object

  3. S

    Inverse square law of gravitation and force between two spheres

    I recently encountered this problem on a test where the solution for the above problem was given as follows: $$F= \frac{Gm_1m_2} {r^2} $$ (1) but $$ m=\frac{4}{3}\pi R^3 $$ substituting in equation (1) $$F= \frac{{G(\frac{4}{3}\pi R^3\rho})^2 }{2R^2} $$ where r=radii of the two spheres m=mass...
  4. J

    What is the relationship between angle and static friction?

  5. SpectraPhy09

    Plotting the graph of Friction Force vs. time (Laws of motion)

    F.B.D Of first block (I have shown only the horizontal Forces) f1(max) = μ (1kg)(g) = 0.5 * 10 = 5N F.B.D Of the second Block f2(max) = μ (3kg)(g) = 15N Now the string will become taut and the tension will start acting when f = t = 5N But for 0<f<5N there will be no motion between the 1 kg...
  6. Istiak

    Velocity along the cylinder axis

    Since the question says that "velocity along the cylinder axis" and "magnetic field perpendicular to the cylinder axis". So cross product of velocity and magnetic field becomes their magnitude. ##\vec v\times \vec B=||v|| \\ ||B||## So ##\vec F=qvB## ##mg=qv\frac{\mu_0 nI}{4\pi r}## At first...
  7. Istiak

    Find force on a particle at time t

    My attempt : ##\frac{\vec Ft^2}{2}=m\vec s## ##s=\frac{Ft^2}{2m}## ##P=\frac{W}{t}## ##k=\frac{\vec F\cdot \vec s}{t}## ##k=\frac{F^2t^2}{2mt}## ##k=\frac{F^2t}{2m}## ##F=\sqrt{\frac{2mk}{t}}## But there was an option which was ##2\sqrt{\frac{mk}{t}}##. And my assumption was that it was...
  8. rudransh verma

    Contact and electromagnetic force

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  9. rudransh verma

    Three blocks pulled by a force

    $$a= -40/(10+6+4)$$ $$a=-2 m/s^2$$ Taking one mass of 10 kg. $$T-40=10(-2)$$ $$T=20 N$$ This is correct. But if I make the eqn of the system then $$-40+T-T+T-T=20(-2)$$ I have also drawn the diagram. It looks like the second body m2 is subject to no force. But it’s accelerating. How?
  10. D

    Net force and position of objects in space

    Q1a) - My current wrong answer is <-5.9e7, -3.3e8, -2.17e8> I used the Fnet = Gm1m2 / d^2 <unit vector> But i keep getting a dif answer each time Q2a) - I thought i could find net force and then divide it by the mass, and multiply it by the time interval. However I got the answer <-4.5, 4.5...
  11. U

    Hydraulic lifting force of this arrangement of pipes

    Hello All, :) Please see the picture , input force F1 and area A1 and second area A2 are all same for 3 cases . in case 2 and 3 , red open outline represents a free-to-move , ie , "T" piece move upward for the 1st case , output force F2 should be F2=A2/A1 x F1 , by pascal's principle ...
  12. U

    B Can the output forces for F3 and F4 be the same as F2 in hydraulic lifting?

    Hello All, pls see picture , input force F1 and area A1 and second area A2 are all same for 3 cases for the 1st case , output force F2 should be F2=A2/A1 x F1 , by pascal's principle , what about output forces of F3 and F4 ? can be same as F2 ? how i calculate them ? thanks
  13. W

    Understanding the Force of Two Cubes

    The solution is : The pressure inside the solid is zero and outside it equals atmospheric pressure, 1.01 × 10^5 Pa. Thus, the force is given by: F =pA = 1.01 × 10^5 × (0.25)^2 = 6.3 × 10^3 N I do not understand why only the area of one cube is used in the solution, should it not be the area...
  14. mopit_011

    Force on three Bolts holding up a Jet Engine

    My solution was that there would be a force of 0 Newtons on the bolt as the bolt is not moving. But this answer is wrong. Where am I going wrong?
  15. S

    I Gravitational force equation derived from GR

    Hello everyone, I know that GR equations are complicated and beyond my scope. But does GR give a simple gravitational equation: Force (as we know it) as a function of distance? (without any complicated tensors). - If yes. What is the equation? Does it give us something similar to Newtons...
  16. J

    I What is the difference between charge and force carriers?

    I'm a bit confused about what difference there is (if any) between charge and force carriers. I imagine charge as a field around a particle that pushes or attracts other particles. But we're also told that bosons mediate the forces by exchanging. So there seems to be a redundancy unless charge...
  17. S

    Force required to drive the Trommel

    I have to calculate force required to drive the trommel? I don't know how will i calculate the kinetic coefficient of friction of bearings? can some please guide me?
  18. A

    I Modeling the concentration of gas constituents in a Force Field

    Say there is a gas made up of two gas molecules: Molecule A and Molecule B. Molecule A has a mass: ma and mole fraction: na. Molecule B has a mass: mb and mole fraction: nb. The gas is at thermal equilibrium and has a constant temperature throughout itself (T) everywhere. It is placed in a...
  19. G

    B Maximum Force on transom of a boat under acceleration

    I'm trying to calculate the maximum Force in PSI applied to the transom of a planing boat under acceleration using F=ma. boat mass is 300kg accelerates from 0 to 10m/s in 6 seconds F=ma -> 500N = 300kg *(10m/s/6s) = 112.4045lbf the contact area between the boat transom and motor is 1000 mm2 =...
  20. U

    Calculating Force to Push Steel Rod Up 50 cm

    Hello ,all I'm calculating the force that required to push steel rod up 50 cm into water filled steel tank . pls see picture . If i exclude negligible friction force (which is friction between steel rod and water sealing gaskets ) Total Force = Force to lift 40 kg rod + Fluid Force...
  21. Arsene11

    Newton's law question involving force and acceleration

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  22. S

    Weight of gold chain when dropped on a weighing scale

    The force exerted downwards on the scale by the chain when it is kept on it would be Fg= Mg =λLg where λ is the linear mass density However when the chain is dropped onto the scale it exerts an additional force due to its change in momentum The force exerted by each part of the chain would...
  23. E

    I Force of gravity on JWST while orbiting L2

    When the Webb is at a point on its L2 orbit, (not at L2), what direction is the centrifugal force vector compared to the direction of the combined earth-sun gravity vector on the opposite side? Is the direction of this centrifugal vector ALWAYS parallel to the sun-earth plane? or is it always...
  24. Truffle98

    Help calculating force needed for a robot's basketball shot

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  25. S

    Problem of spring block system: force vs conservation of energy

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  26. samy4408

    I Positive Charges: Explaining Motion Despite Net Force = 0

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  27. D

    How to prove that a force is conservative?

    I have done this question and also seen the model answer but i just want to check my method is ok. I differentiated the position vector twice and multiplied by m to get the force F. I then used the determinant method to find the curl of F which i found to be zero thus proving the force is...
  28. patric44

    I What is the origin of Lorenz force?

    hi guys one of my friends asked me about the origin of the electromagnetic induction, I know somehow that its related to the Lorenz force as the electrons in the conduction band of say the coil interact with the magnetic field ,which results in separation of electrons and positive ions which...
  29. S

    Force to Close/slam a steel door gate

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  30. T

    I Impulsive force and simple integration

    May I ask if the following process is correct? Given: F=ma Apply an impulsive force using the dirac delta near 0 (with F nearly constant over the tiny impulsive interval) ma = Fδ(t) This is a second order differential equation with a forcing function. However, I cannot readily integrate...
  31. A

    Unbalanced force to find altitude of airplane

    Since the airplane is flying at a constant speed, then the lift force equals the weight of the airplane. This means that the lift force prior to acceleration is the mass * gravity constant = 29400 N. When the airplane increases horizontal speed, the lift force increases to 30 kN. This means...
  32. L

    B Can Inductive Reasoning Explain the Movement of Strings on Spools and Bikes?

  33. P

    B Confused about force body diagram for 2 body collision

    I'm trying to understand Newton's third law in the context of collisions. Assume that one body has mass M kg and is traveling in the positive x direction with acceleration A m/s^2. Assume that the second body has mass m kg and is traveling in the negative x direction with acceleration a m/s^2...
  34. D

    B Why Does a Body Experience Fictitious Force on Accelerating Objects?

    Why does a body experience a fictitious force when placed over an object which is accelerating ? I mean why it doesn't just accelerate with an object... What's actually happening?
  35. A

    I Conversion of Fluid Rotational Force to Rocking Motion

    Does anyone know how to convert the parameters within constraints to equate rocking motion from fluid being mixed through consistent shaking? What I am given: Centrifugal Force Calculations: mass = 0.25 kg angular velocity = 12.57 rad/s radius = 0.045 m What is known about the bag of fluid on...
  36. I

    I Resulting force on a chamfered pneumatic piston

    I was reading up on forces on hydraulic/pneumatic cylinders, and I've been thinking of this for a while: So for a pneumatic cylinder, the force on the piston is simply: P = F/a F = P x a where a = area of the piston that the air pressure is acting on. So what would happen if the piston is...
  37. R

    I am calculating the forces on String cheese with net force = 0

    Here is the link to the question. https://www.khanacademy.org/science/physics/forces-Newtons-laws/Newtons-laws-of-motion/a/what-is-Newtons-second-law What is the magnitude of the force F1 ? What is the magnitude of the force F2 ? Here is my drawing I made At this step I am lost. ## ay...
  38. A

    B Newton's second law of motion -- Why is it F=m*a and not F=m+a?

    Why F=m*a i.e product or multiplication and not F=m+a? i.e addition or summation?
  39. Eobardrush

    Why momentum of a ball bounced off a wall increases twice fold?

    Question 2a: It is really hard for me to get my head around this. The solution of this question mentions the momentum of the ball after it rebounds is 12kgms. My attempt at this solution is as follows Before collision Momentum of ball= mv= 2x3= 6 kgms and momentum of wall= 0 Therefore Total...
  40. D

    Magnitude of force acting on wedge and block

    Clearly if ##F = 0## and ##\tan\theta > \mu_s##, then using the above equations for ##f_s## and ##n##, we get ##f_s > \mu_s n## so the block will slip. However, it seems that as long as the force ##F## is directed to the right with a certain minimum magnitude, namely ##\frac{\tan\theta -...
  41. Lunct

    B Gravitational Force acting on a massless body

    It's a well known fact that acceleration due to gravity is independent of the mass of the accelerating body, and only depends on the mass of the body it is accelerating towards and the distance from it. One can prove this mathematically very easily. F=GMm/r^2 (equation 1) but also F=ma...
  42. F

    I Mechanical power generated by a force F

    Hello, It is well understood that a constant horizontal force ##F_{applied}## applied to an object of mass ##m## over a distance ##d## in a direction that is not orthogonal to the direction of motion produces mechanical work ##W= F d ##. This work is a mechanism to inject (or subtract) energy...
  43. O

    I Fluid force from a fluid flow vs. from a fluid jet

    In fluid flow (such as wind), the force exerted on a perpendicular surface is derived from kinetic energy and is ρAv^2/2. But in problems involving a jet of fluid that strikes a plate, the force is derived from momentum and is explained to be ρAv^2, lacking the 1/2 factor. Can someone please...
  44. A

    B Is the weak nuclear force attractive or repulsive or both?

    Hi Of the 4 fundamental forces, I did not understand the weak nuclear force. Is the weak nuclear force attractive or repulsive or both? It works between two particles, that is, it is the interaction of two particles?
  45. LCSphysicist

    Electric force due to a moving charge

    I am having some problems involving the force that a source moving with speed v along the x-axis would exert on a test charge at the x axis. Moving to the frame of the source charge, we got that the electric field it exerts is $$E' = kq/x'²$$ Now, moving back to the lab frame, and considering...
  46. I

    Calculating the Force of a Jump on the Moon

    From my understanding, at an elementary physics level, the height at which we can jump depends on acceleration due to gravity and the initial velocity when we leave the ground. We can calculate our initial velocity by calculating acceleration and using the distance we bend down before jumping to...
  47. D

    Friction force on each foot and on each hand of a person

    I get how to solve (a); my method involves finding the net torque about the man's hands and setting it to zero, which can be used to solve for the normal force acting on his feet and the normal force on his hands can be solved using Newton's first law. Then divide by 2 for each to get the normal...
  48. kara123

    Finding Friction Force & Work with No Applied Force

    -i had begun by finding the normal force =147 N -then found the force of friction=99.96 N -found the work of friction=-799.68 J after that I am unsure of where to go since I don't have a force applied
  49. G

    B Resultant force in vertical circular motion

    Suppose we have a vertical circular motion with gravity according to the image below. In the leftmost and rightmost positions the resultant force is pointing diagonally down. Isn't the resultant force supposed to be pointing at the center at all times in a circular motion? What am I getting...
  50. S

    Finding the position of a middle charge to have Zero Net Force

    Hi! Given three voltages as follows; Q1 = 1C,Q2 = 1C,Q3 = 2C The distance a is 1m and b = 2m a) Find the values of the forces that are acting on Q2 I did that like this; $$ F_{12} = \frac{Q1*Q2}{4\pi\epsilon r^2} $$ $$ F_{32} = \frac{Q1*Q3}{4\pi\epsilon r^2} $$ The results are ...
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