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. M

    Piano rolling down a slope

    Albeit the simple question, I am a bit confused on whether the correct answer choice is (B) or (C). When the piano is slowing down, shouldn't the force received by the piano be a bit greater than the force received by the man?
  2. Mohmmad Maaitah

    Stress on a pipe

    Hi, I've problem thinking about this problem isn't the force acting on "nothing"? how can there be any stress, I'm lost!
  3. mister i

    B Can the force of gravity overcome the Planck force?

    Can the force of gravity overcome the Planck force? I remember that a long time ago I read that in the universe the Planck force was the maximum force that could be reached. But when Sagittarius A and the black hole at the center of the Andomeda galaxy approach, I have made the calculation that...
  4. C

    I Work done by a non constant force over a non constant angle

    I was just wondering if I needed to set up this double integral or not. I've never seen anywhere people setting up double integrals for calculating the work.
  5. C

    Magnetic Force in Parallel Magnet Setup: Exploring the Strength of Attraction

    Imagine two parallel lines of five magnets each, spaced a few millimeters apart. In the first line, all magnets have their north poles facing one direction. In the second line, each magnet's south pole faces the corresponding north pole of the first line, but the magnets are offset by one along...
  6. S

    B Newton's 3rd Law interactions with 2nd and 1st Law Partners

    I was over on the stack but got asked to move over here. https://physics.stackexchange.com/questions/804903/newtons-3rd-law-force-on-a-rocket I've been at it all day trying to understand what partner forces are and how you can have a change in force with regard to them, or why gravity is...
  7. Juanda

    I Pushing a rod in a magnetic field

    I will present the case as an exercise because I believe it will be easier to understand that way. I didn't know if I should post it under the mechanics or electromagnetism sections because I am actually trying to link both. Since it feels like a fairly simple problem, I considered the Classical...
  8. M

    Help calculating force required to flange a cylinder

    Need help in calculating the force required to flange a cylinder outwards around the perimeter by approx. 5mm. Cylinder is either Aluminum or standard Mild Steel. Thank you.
  9. K

    Dark side of the moon...

    Dark side of the moon! I can understand that Selena Gomez I've been down the darkest alleys Saw the dark side of the moon in Wolf or Transformer movie use that phrase, But this is US Space Force, of all people! US Space Force
  10. Ineedhelpwithphysics

    Sign of Work (Negative or Positive)

    Im confused I did 850*9.8*14.7 = 1.2x10^5 Why is it not negative since the force is opposite to the motion?
  11. S

    Spinning a Bucket to measure gravity with the parabolic surface of the water

    I did (A) by balancing force on point p (in the figure). I found slope , tanθ = (w^2)x/g. I dont know what to do next. Pls help
  12. R

    B Help with science experiment magnets/force/acceleration/speed

    Sorry, I guess I should have remembered all of this from my school days, but right now I have forgotten so much that I need some help. I am developing some simple experiments for school children (age ca. 12). This one involving magnets. I am not asking for detailed calculations, that is way...
  13. MatinSAR

    Find force as a function of position: F=F(x) using v=v(t)

    If we consider ##v=-3t^2## then: $$x=-t^3$$$$a=-6t$$ Using ##t=-x^{1/3}## we have : ##a=-6(-x^{1/3})=6x^{1/3}##. My answer suggust that ##F=Ax^{1/3}## but in options we have ##F=-Ax^{1/3}##. Can someone guide me where my mistake is?
  14. W

    Two masses on a slope with a connected tension force

    I derived an equation but I have no idea how I can find the mass of the unknown without the normal force in either the x or y direction
  15. chwala

    Calculate the magnitude of driving force on the car

    My approach is as follows, let ##D## be driving force and ##F## the force resisting motion, then ##D-F = 850 × 0.3## ##D = 250 + 255## ##D = 505## Also, Force parallel to the road is given by, ##F_1 = 8500 \cos 78^0 =1767.24 N## Therefore, the magnitude of Driving force is given by, ##F_1 +...
  16. S

    I Conductors and circuits for nuclear force

    Is it possible to create something like a circuit powered by the strong nuclear force rather than the electromotive force of a battery? If so, what would be examples of some conductors and resistors that could go in such a circuit?
  17. C

    Force on a charge from a nearby charged rod

    Hi! My attempt at this solution was: ∫dF = k*q*Q / 2L ∫ (1/r^2) dy and we know that r^2 = D^2 + y^2 based on the diagram. Here is where I start getting confused. I looked at a different physics forum post and the mentor gave this equation: I am mainly confused with the math. How did he end...
  18. R

    What is the y-component of the force by the floor on her during the collision?

    A previous question I got correct was: During this time interval, what is the y-component of the average net force on her? It was just 2625, and I thought question 2 would be the same answer but it wasn't. Not sure what to do.
  19. A

    I Do the plates of the capacitor exert a force on each other?

    Do the plates of the capacitor exert a force on each other due to opposite electrical charges? Consider a planet capacitor. A simple calculation shows that this force must be very large. If you are not convinced of the magnitude of the force, I will give a simple example.
  20. C

    E&M: Forces resulting from Charges at the Corners of a Cube

    My first attempt at solving: I divided up the point charges based on the radius away from point A. 1 charge was s*sqrt(3) away, 3 charges were s*sqrt(2) away, and 3 charges were s away from point A. q remained constant. Therefore, my F_total was: F_total = k * [(q^2 /...
  21. M

    Force between poles of two magnets

    The Biot-Savart law gives us the magnetic field created by an electric current. We can calculate the force exerted on a moving charge by this magnetic field using Lorentz's force formula. But my textbook doesn't address the repulsive or attractive force between like or unlike poles...
  22. Quantum Psi Inverted

    Balancing Torques and Forces on this Beam

    In the given solution, it states that F_3f(a)=F_2f(a+b) is a "reasonable assumption". However, I don't see how we can just assume that. I can very clearly see that F_i for i=1,2,3 is likely proportional to a and b in some kind of way, but I can not clearly establish a line of reasoning for this...
  23. R

    I Advice regarding sled experiment

    Hello. I would like to design an experiment where different sled designs are compared. Specifically, I would like to asses how sled design affects the amount of force required to pull a sled over 100 meters. Any suggestions you might have would be greatly appreciated.
  24. K

    I Unit Conversions of Force: How to Convert Between Different Units of Force?

    Hello. Im studying for an exam and came across this simple unit conversion question but I haven't done something like this in a long time! I understand the conversions of each unit individually but get a bit stuck combining them. This is the question: A force of 100 N is exerted on an object...
  25. M

    B The Force of protons and quarks?

    How much force will it required to pull a quark out of a proton, and how much for to pull a proton out of a atom ?
  26. MantisShrimp

    How much force can a truck seat back cushion absorb during a collision?

    I do not know much about this, please help. My truck seat back cushion is 2" thick. Truck A is ~5,700 lbs from google. 2011 f-150 super cab 6.5ft bed. Truck B is ~5775. 2015 GMC Yukon xl slt. If truck A is stopped and braked and truck B hits truck A going 45-55mph creating a force of...
  27. Lotto

    Why can we move the spring with constant speed when we apply a force?

    One solution is that if we move with the same velocity as the spring does, the initial velocity of the block will be ##v## and the final will be zero, so its kinetic energy will transform into a potential energy of the spring. I would also say that we can say that if we pull the spring, we...
  28. L

    Confused about resolving Tension and Weight

    Calculations with 1: T1sintheta + T2sintheta = W T1costheta = T2costheta Calculations with 2: Wsintheta = T1 Wcostheta = T2 These are not equivalent. Can someone point out the flaw in my logic? Edit: System is in equilibrium!
  29. biomajor

    Would one be pushing as much as their weight?

    Because one is effectively pushing in the same way as a chest press machine, wouldn't the work done be the same?
  30. E

    B Magnetic attraction force Question

    Other than the most simple school stuff of attraction, repulsion and "lines of force", I've never studied magnets. Hence this question. On the left we have a disc magnet diameter D attracted to a much larger lump of steel with force F (when there is no gap between)...
  31. D

    Conservative forces in circular motion?

    TL;DR Summary: The rigid object move around the circle with constant force how it possible the force
  32. SacCno

    B Help Scaling Gravity Simulation

    I'm trying to make a 2D game on Unity similar to Universe Sandbox 2. I currently am working with a star and planet, both with roughly the masses of the sun and earth respectively for comparison and at a distance of 31,000,000km. My current model uses Newton's formula for gravitational force (F...
  33. 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...
  34. 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\\...
  35. 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.
  36. 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?
  37. 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...
  38. 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
  39. 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...
  40. 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?
  41. 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?
  42. 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?
  43. S

    Towing two stacked boxes up a ramp

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

    Jackhammer on Vehicle Suspension, Unsprung Mass, Tire patch load

    Hello all, I wanted to know what would happen if I put a jack hammer system on the unsprung part of the suspension, I posted this on the engineering forum but couldn't get a complete answer. https://www.eng-tips.com/viewthread.cfm?qid=512117 Basically the argument was if the reaction would...
  45. mazia

    Questions Regarding a Cat Going Up a Ramp

    EDIT: I've finally found the solution, so here's what I did. First, calculate Work using the equation: (F-mgsin(theta))*displacement, where F=the force being applied by the push, theta is the angle of the ramp, and displacement is the length of the ramp. Now that you have the value for work...
  46. 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
  47. 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...
  48. K

    Need help calculating maximum stress in a bolted assembly

    Trying to calculate the maximum stress that would occur in the attached assembly... The assembly consists of a tube sandwiched between two plates that are bolted down to a larger plate with an M6 bolt. Each of the two plates have a 400N force acting on them which is perpendicular to the axis of...
  49. D

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

    Hi. I have a problem I'm trying to solve. I have a tarp that is stretched horizontally across two walls. The walls are 5.5m apart and 50m long. There is a pressure of 10mBar above the tarp pushing it down, making it sag about 0.15m in the center. I'm trying to calculate the force with which the...
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