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. 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 /...
  2. 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...
  3. 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...
  4. 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.
  5. 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...
  6. 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 ?
  7. 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...
  8. 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...
  9. nafisanazlee

    Minimum force required to keep two blocks from not falling

  10. 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!
  11. 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?
  12. 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)...
  13. D

    Conservative forces in circular motion?

    TL;DR Summary: The rigid object move around the circle with constant force how it possible the force
  14. 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...
  15. 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...
  16. 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\\...
  17. 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.
  18. 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?
  19. 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...
  20. 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
  21. 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...
  22. 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?
  23. U

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

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  24. Memo

    Moment of force, rod with mass

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  25. S

    Towing two stacked boxes up a ramp

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  26. 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...
  27. mazia

    Questions Regarding a Cat Going Up a Ramp

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  28. yashboi123

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  29. 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...
  30. K

    Need help calculating maximum stress in a bolted assembly

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  31. 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...
  32. P

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

    This is how I tried to do it, which is the most direct. The force that the mass exerts on the spring is mgsin(53). and I equated that to kx. and found x. but apparently, this is wrong and the teacher told me a different method. (ME)1=(ME)2 due to conservation of mechanical energy...
  33. 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##?
  34. Nova_Chr0n0

    Engineering Resultant Force and Direction using Parallelogram Law

    Picture above is the complete question. I want to ask about the problem where I would use the parallelogram method. Here is my FBD: I start off by computing the angle alpha: α + α + 105 +105 = 360 α = 75 degree After that, I now use cosine law to solve for the resultant force...
  35. D

    What is the Resultant Force from adding these two forces?

    when is apply the formulae of resultant force for the two equations the angles cancel out and I can't get any value for the angle when i add the two equations: R^=f1^2+f2^2+2f1f2cos(theta) squart3*R=f1^2+f2^2-2f1f2cos(theta)
  36. Ggb

    B Coulumb's Law at 1 light year distance

    Hi, What happens to the force when the particle are kept at 1 light year distance. I agree practically the force would be very weak because of inverse square law, theoretically what happens to the force?
  37. A

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

    I'm looking for advice on how to calculate the force needed to putt a golf ball on a level green a certain distance. I currently have the mass of the golf ball (45.93g), distance (3.048m), and the rolling coefficient of friction using a stimpmeter reading. I have started by creating a free body...
  38. 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...
  39. 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...
  40. E

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

    I have to show that the force is non-conservative, i.e. that work done for the round trip ##\neq 0##. Rearranging the circle equation, I can say that:$$x = \sqrt {R^2 - y^2}$$$$y = \sqrt {R^2 - x^2}$$ Then I have:$$F_x = -\sqrt {R^2 - x^2}$$$$F_y = \sqrt {R^2 - y^2}$$ Now, as I understand it, I...
  41. S

    Determining Maximum Torque in a Truck and Forklift System

    This maybe complex and complicated - I know its going to be multi step. Please see attached picture. It involves velocity and weight and gravity torque force, pivot points.
  42. 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...
  43. S

    I When Water acts like Glue (flat surfaces)

    Water like glue This topic could have more meaning on a chemistry forum. Firts of telling my doupt, i will inform you why i put this question. My goal is controlling an obejct more accurately. I notice that sometimes a solid with plain face on a wet surface is difficult to remove. Besides it...
  44. jr5

    Determine Force for inclining platform

  45. 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...
  46. 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...
  47. 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...
  48. 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...
  49. 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?
  50. 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!
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