What is Forces: 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. 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...
  2. 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...
  3. 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...
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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...
  10. 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.
  11. 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...
  12. 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...
  13. 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?
  14. 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...
  15. 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...
  16. 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...
  17. 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...
  18. 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?
  19. 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...
  20. K

    Engineering Fluid Mechanics Problem: Water Forces on a Parabolic Gate

  21. 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...
  22. 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.
  23. 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...
  24. 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 ...
  25. 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...
  26. M

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

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

    Lorentz Forces: All the Details You Need to Know!

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  28. 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".
  29. 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?
  30. 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
  31. 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
  32. 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...
  33. 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 =...
  34. Ahmad Qaimari

    Vectors physics homework -- Addition of two vector forces

    Trying to solve it
  35. 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...
  36. 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...
  37. 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...
  38. 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...
  39. 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...
  40. 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...
  41. 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...
  42. Chuzzled

    What are the forces acting on the container?

    Let’s say I bring a closed container full of air into deep space where atmospheric pressure is is near 0. I Open the lid and then the air moves out of the container and into the vacuum of space. What are the forces on the container AFTER the lid has been removed? Does the container move...
  43. E

    Calc Forces on Pulleys: 200N, 300N Masses, No Friction

    Homework Statement: In Figure 3-25, the weights of the objects are 200 N and 300 N. It is considered that the pulleys have no friction and that their masses are negligible. Pulley P1 has a stationary axis, the P2 pulley can raise or lower freely. Calculate the tensions FT1 and FT2, as well as...
  44. K

    I Equation for levitation forces between the magnets and superconductor

    How can I measure the levitation forces between the magnets and a type-II superconductor (YBCO superconductor)?
  45. A

    What mistake did I make when solving for the equilibrium of a rigid object?

    Here's the task: My attempt at a solution (I choose C as an axis): However, the textbook solution says D should be 58.8. What am I doing wrong?
  46. R

    Understanding Shearing Stress & Tangential Forces on Fluids

    what does it mean that fluid cannot sustain a force that is tangential to its surface.which surface fluids's surface or container? and what does it mean it cannot withstand shearing stress.what's shearing stress and what does it mean here.and why exert force only in direction perpendicular to...
  47. J

    What forces are acting on an object during a bounce?

    This is not a homework question. I merely am interested in what forces are acting on it.
  48. J

    Forces and vectors: pulling a baby buggy on soft ground

    I don't know exactly where to start with this problem. But I'm going to try this, cos θ= adj/hyp cos 40° = Fx/100 Fx=100 cos 40° =76.60= 77N??
  49. Kaushik

    Internal forces and the work done by them

    My book states that, '∑Finternal=0∑Finternal=0. But the work done by them may or may not be zero. Why is this true? Edit: How can the work ≠ 0 sometimes?
  50. J

    Calculating drag and pressure forces from numerical simulations

    So as stated, I am calculating the pressure and drag forces on an obstacle, but have trouble with which velocities to take. This is my geometry: http://shrani.si/f/3l/13P/2Tihb3iM/projekt2.png . I am guessing that I have to take pressure just before the obstacle and just after the obstacle and...
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