Forces Definition and 1000 Threads

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

    Forces exerted on an anchor point from a falling object

    Hi, I'm looking at the forces exerted onto an anchor point when a n object is dropped but is secured to that anchor point witha steel wire rope lanyard. i can find this but not sure if it is relevant or not to my investigation: Fmax = mg + sqrt(2mg x E x A x fall factor +(mg)2 ) The mass is...
  2. L

    Velocity change under drag and other forces: small mass, large delta-t

    I am working on simulating the movement of small spherical objects under the influence of drag and a number of other forces that, at least for now, don't depend on the object's velocity. Normally I would sum up all these forces, including drag, to ##F_\Sigma## and update the object's speed...
  3. S

    Inclined Plane Forces - with a twist

    Hi Smart People, I have spent a lot of time on this and have looked in Reed's and Wallker's applied mechanics but can't find a clear explanation. Calculating the force required when pulling up an inclined plane whether horizontally to the plane or at an angle seems pretty straight forward...
  4. wnvl1

    How Can I Solve for the Forces on Pruning Shears with Three Subsystems?

    First subsystem: $$C_x + F_{DE} \cos(45) = 0$$ $$C_y + F_{DE} \sin(45) + 20= 0$$ $$F_{DE} \sin(45) \times 25 + 20 \times 150= 0$$Second subsystem: $$B_x - C_x = 0$$ $$B_y - C_y - A_y - 20= 0$$ $$-F \times 150 + A_y \times 60 - C_x \times 30 = 0$$Third subsystem: $$-B_x - F_{DE} \cos(45)...
  5. polytheneman

    D'Alembert's principle and the work done by constraint forces

    From what I understand, constraint forces do no work because they are perpendicular to the allowed virtual displacements of the system. However, if you consider an unbalanced Atwood machine, in which both masses are accelerating in opposite directions, you'll find that the tension force of the...
  6. B

    Bow & arrow -- Forces on the Bow

    Hello everyone! So I have been doing this projectile motion question and do not understand how to do work out which forces act on the archer's left hand in part a)i? I am specifically told to ignore the weight of the bow & arrow. But this is force that only acts downward for the bow & arrow...
  7. H

    Magnetic forces on current-carrying wires

    please correct me if I'm wrong. is it for the question b, F/l= 0.50 right? does that mean the resultant magnetic force at X is determine by the force at Y and Z? do I need to consider the direction to solve the equation? first step to know the direction of each conductors I use the right hand...
  8. mmaismma

    How to Solve Hinge Force Problems?

    I have solved problem (A). But I couldn't solve problem (B). Here is my attempt:
  9. B

    Perpendicular forces acting in x and y directions

    Hi everyone! So I got a question shown below here and I’m struggling in what the question is trying to say here and what it wants me to give? Here is what I done For when resolving the individual x and y component of forces, my angle has always been measured counter clockwise from the...
  10. P

    B Conservative and Non Conservative Forces

    I was referring to the conservative and non conservative forces. When i was thinking about it for example when i apply force on an object on the table the object moves a distance and when i remove the force the object does not come back to original position. Can i assume that the force i apply...
  11. Vigardo

    Forces in a Howe truss (2D) pinned at BOTH ends

    Dear experts, How would I find the forces for the truss with both ends pinned? (Fig.1, bottom) I'm trying to determine the forces in all members of some trusses. I've successfully applied the method of sections to a Howe truss (top truss in Fig.1) and I' ve verified it by FEA with MecWay...
  12. Adesh

    A proof that magnetic forces do no work?

    The proof of magnetic forces do no work is given in Introduction to Electrodynamics by David J. Griffiths like this My problem is why he has replaced d\mathbf{l} with \mathbf{v}dt? This substitution implies that the charged particle was moving with \mathbf{v} only and no force acted on it...
  13. S

    A Standard Model and number of fundamental forces

    Just a curious question, is there a limit within the standard model on how many fundamental forces there can be? I have some familiarity with particle physics/QFT(not quite mastery obviously otherwise Id probably be able to answer this myself) and the thought popped in my head when reading about...
  14. T

    How forces act on a shape and its centre of Mass

    Hello all After a lot of support from people like Dr.D, mfig and collinsmark I have finally understood the concept of Centriods and Centre of Mass. I am now trying to understand how a uniformally distributed force and a non uniformally distributed force acts on a shape. If I had an oddly...
  15. MPavsic

    Belt and Pulleys - Centrifugal Forces

    Hi. I assume that vector summation of the centrifugal forces acting on the belt, on pulley A and B, equals to zero. Is Centrifugal force on pulley A static or dynamic force? What would, hypothetically, happen if the sum centrifugal forces acting on the belt are not zero? Could some kind of...
  16. W

    B Forces inside a moving elevator

    For some reason this is something I have really hard time wrapping my head around. Suppose you are sitting on a chair inside a completely closed elevator. The elevator might be moving vertically at a completely constant speed, or it might be completely stationary. It is my understanding that...
  17. T

    Forces On a Moving Train Traveling Around a Curve

    Hello all I am trying to work out the forces involved of a moving train around a curve traveling at a constant speed. I have the following:- The image on the left is a cross section of a train traveling around a curve, you can think of the train moving away from you. The image on the right...
  18. posto002

    How Can I Improve My Algebra Skills for Solving Equilibrium Problems?

    I got the equation --> d=mL/[2*(√(2M)^2-m^2)] where M is one of the masses at either end (multiplied by 2 because... there's two of them.) and m is the mass in the middle of the system. Something that a TA told me was that L, the horizontal distance of the system changes. I'm confused by this...
  19. T

    Why does the resultant Fy have opposite values in my calculations?

    Hello all I was hoping someone could explain why the resultant Fy has a value of +40kN but I get a value of -40kN.
  20. minadd

    Find all forces & the coeff. static friction of a pulley at equilibrium

    Given: (block a) m = .500kg (block b) m = .200kg that's all... Fg (block a) = (.5)(9.81) = 4.905N = Fn Fg (block b) = (.2)(9.81) = 1.962N i think acceleration might go like... a = (1.962)/(.5 + .2) = 2.8m/s^2 but isn't it supposed to be at equilibrium? So 0m/s^2. How am I supposed to find...
  21. melissafern

    Find the forces applied to a rotating level

    Homework Statement: Solve parametrically the system with g, load cell measurements and know accelerations. Homework Equations: to be found Consider that we know angles tetha(t) of a mass-less link rotating about its centerr O. - so we also have velocities and accelerations - and values of...
  22. kepherax

    Using Forces and Torques to solve a pulley problem

    I am able to solve this easily using energy conservation, but I'm curious how one would go about solving this using forces and torques?
  23. J

    Help Walk Me Thru Motor Sizing Calculations Please

    Summary: Hello; i am trying to work my way thru some motor sizing calculations on a semi-simple example so that i can more easily do it in the future. Could i get some guidance? Hello: I am trying to develop a good system for sizing motors (generally steppers). In the past i just guesstimated...
  24. O

    Teaching Forces - Having issues with directions & vectors

    Hi everyone. I'm the only physics teacher at my school, so I have nobody to bounce ideas off of. I'm having a problem with students getting confused with direction when calculating net force. I teach an introductory physics course. It's the first time the students have ever seen physics and...
  25. T

    Help With Understanding Resultant Forces By Connecting Vectors

    Hi all I am trying to get my head around resultant forces. I am happy that if I have a vector diagram with 2 forces I can work out graphically the resultant forces by connecting the head of one of the vectors to the tail of the second vector. The confusion comes in when I have 3 or more...
  26. Like Tony Stark

    Forces applied by a slot on a slider

    What forces are exerted by the slot on the slider? You have a normal force since it's inside it, and that's the only force that I can imagine. But then? I think about the pseudo-forces since it's on a rotating reference frame (centrifugal force, Coriolis force, Euler force), but those forces are...
  27. T

    Calculating Centrifugal & Coriolis Forces at Rest

    so I can find the centrifugal force but shouldn't the Coriolis force be 0 because the mass is at rest?
  28. Like Tony Stark

    Exploring the Effects of Coriolis and Centrifugal Forces on Railway Motion

    I think that there could be friction, but I try to think on forces related to the motion along the Earth, which rotates. Like when you're on a car that turns to the left and you feel pushed to the right. Do the wheels do the same to railway? Would there be Coriolis force? Because that's just...
  29. K

    Engineering Fluid Mechanics Problem: Water Forces on a Parabolic Gate

  30. Physics4Eva

    I Could the Discovery of the Graviton Connect Quantum and Classical Physics?

    W and Z bosons, gluons, and photons are all gauge bosons that have been found. Since the graviton can be connnected to atoms and mass in certain ways, I think that CERN may eventually prove the graviton(if real) through smashing atoms that, supposedly, have a graviton orbiting them. Could...
  31. LilRubyKinz

    How to Solve Acceleration of Cart on 3 Different Slopes?

    I am trying to solve accelerations of a cart on these different slopes. I don't understand how it is possible without knowing the coefficient of friction, but my teacher says it is (very cryptically I might add). Can anyone help me understand this? Thanks.
  32. S

    Using Newton's Laws: Friction, Circular Motion, Drag Forces

    Here is my attempt at setting up the equation: I set up the equation to find the acceleration of the box: F-Ffr= m*a after finding the acceleration, I can use the acceleration and plug it in the formula v^2=(v0)^2+2*a(x-x0), which will get me the value of (x-x0)The solution sheet says that F...
  33. Like Tony Stark

    Forces acting on a block which is lying on another block

    Well, I'm having trouble with the free body diagrams. For ##A## we have ##y)## weight, normal force, contact force with ##B##, ##F . sin(36.8°)##. And the acceleration is ##0## because we want to calculate the maximun force before moving. ##\Sigma \vec F = m . a_y## ##\vec N_A + \vec F ...
  34. jisbon

    Electric forces between conducting rod and rail

    Alright, to start off: I'm not even sure how this works in the first place. What I do understand is that if they carry current in the opposite direction, using right-hand grip rule, the magnetic field between them will be the same (into the page). Hence using the left-hand rule, I can deduce...
  35. M

    Object movement under the infuence of Forces on the x,y axes

    Which could be the first step to find the V(t) ?
  36. Aagno3

    Lorentz Forces: All the Details You Need to Know!

    Hey y'all Can anyone just tell me every detail about Lorentz forces ? I have a pretty good idea, but i want to surprise everyone in the presentation that i am about to give, so please just tell me whatever detail you know . Every single detail might be helpful . Also , if anyone knows how to...
  37. VictorMedvil

    A Merging Gravity with the other forces

    How mathematically within the confines of mainstream physics would you experts in physics merge Einstein's Field Equations with Quantum Mechanics and Quantum Field Theory? I am looking for a different perspective on this subject usually I get the perspective of "Cranks".
  38. S

    Overcoming Nuclear Forces: A Look Into the Physics of the Atom

    Is it that work is done to overcome the nuclear forces holding the nucleus together?
  39. H

    Calculating the coefficient of friction Given 2 forces and and angle

    i tryed putting all the number into that equation but it does not work, i have no clue if i need to include the angle to solve this or not and if i do i have no clue how i would
  40. J

    Feeling Forces (like feeling gravity while in free-fall)

    a = (change in magnitude of velocity) + (change in direction of velocity) → Can you feel when you change direction? Even if force and acceleration are constant? ↑ ↓ ↑ ↓ ↑ ↓ o
  41. P

    Magnetic Forces & Moving Wires: The Right Hand Rule

    OK so a wire with a current creates a b field in accordance with the right hand rule. Now moving charge will feel a force (if its moving in the correct direction) while stationary charges will not feel a magnetic force. What I am curious about is if we move the wire itself, will a stationary...
  42. PlasMav

    What is the discrepancy between two equations for calculating electrical forces?

    Hello, First of all I want to say that I am not an EE, I am an ME but I am working for an EE laboratory on campus and am trying to get a force from and electrical circuit on a project here. I am using the following equations: F = 1/2*L'*I^2 (where L' = H/m) and F =...
  43. Ahmad Qaimari

    Vectors physics homework -- Addition of two vector forces

    Trying to solve it
  44. Z

    G forces when falling - proper acceleration question

    The question comes from a thought experiment of a rocket approaching the Earth accelerating at a constant rate of 1g from say from a hypothetical "earth like planet" near by. . we would be standing on the floor of the upright rocket as it lifts off, if we are standing on a scale, our...
  45. Gabriel Henrique

    Finding potencial of forces - answer differs from solutions

    The first force components: Fx = ax + by², Fy = az + 2bxy, Fz = ay + bz² I calculated the integral V=-∫Fdr, using dr=(dx,dy,dz) The result I found was -(1/2(ax²)+2azy+2bxy²+1/3bz³) The answer in the book (Kibble's Classical Mechanics): -(1/2(ax²)+azy+bxy²+1/3bz³)The second force: Fr = 2ar sin θ...
  46. P

    Wind Forces on Roof: Calculating Amount of Weight Needed

    For a project I need some dry workspace outdoors, so I build a wooden frame and covered it by a tarp. It's kind of like a carport with a A-roof where one side is 2,4m, the other is 3,6m. Angle of inclination is 30 degrees on both sides. Length of the building is 10m. The roof frame is placed on...
  47. I

    Forces along non-perpendicular axes

    Determine Force from F2 along u and v axes. CompF= F*Cos(angle); CompF onto U = 8kN*Cos(30) = 6.93kN Angle between F2 and V: 180-75 = 105; 105-30 = 75 degrees CompF onto V = 8kN*Cos(75) = 2.07 kN. Since in the -V direction; -2.07kN. I just would like for somebody to verify these answers. I've...
  48. W

    Various objects under extreme g forces

    I have a friend doing an animation of 6 objects under extreme g force. Can anyone offer an opinion on how these objects would look when destroyed by extreme g forces standing on a flat indistructable surface . When will they start to change and be completely obliterated , how would it look? how...
  49. T

    How many G forces did I experience during my head hit?

    Hi, I just hit my head on the top of my car door as I was leaving my car; the hit hurt my head a lot and I am worried that I received a concussion. However, I read that most concussions require more than 65 Gs of force to be classified a concussion which is why I am wondering if someone here...
  50. S_Wildjocks

    Forces acting on a magnet which is deflecting a charged particle

    Summary: Considering a charged particle moving through a magnetic field, what forces does the particle exert on the magnet that is causing it to deflect? Hi all, probably a dumb question, but what force(s) does a charged particle exert on a magnet as it passes through it's magnetic field and...
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