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. J

    Linkage analysis of forces and stresses?

    The attached image shows a linkage mechanism with 2 parallel bars pivoted to a fixed base. The lengths of the the bars are equal. A connecting linkage and gears are used to connect it to a 3rd bar. I would like to know how to analyze this linkage system to find the forces, moments and loads for...
  2. A

    B Why are we trying to unify all the physical forces?

    I've been reading a book called hyperspace by D.R Michio Kaku. In this book he talks about unifying all the fundamental forces of nature (gravity , electromagnetic force , weak and strong nuclear forces.) My question is, what if they are not unified and we are just trying in vain. I don't...
  3. OmCheeto

    What Are the Net Forces Acting on the Kuiper Belt Object Ultima Thule?

    Homework Statement [/B] A Kuiper Belt object, Ultima Thule, rotates once every 15 hours. It has an estimated density of 1000 kg/m^3. Ultima, the larger sphere, has a radius of 9000 meters. Thule, the smaller sphere, has a radius of 6500 meters. The center of rotation is 4200 meters from the...
  4. Green dwarf

    I Why do we need to unify gravity with the other three forces?

    I am wondering why gravity needs to be unified with the other three forces into a super-force. Why can't the three forces be seen as interactions between particles in a space-time fabric whose geometry gives the impression of gravity?
  5. P

    How the forces on a drop of water versus mercury on a glass slide influence the shape?

    I am trying to understand how fluids form particular shapes when put on a solid. In the two figures,what are we taking as a system for the forces? How the resultant of the forces influences the shape of the different fluids?
  6. K

    B Question about forces in a gearbox

    hi all i have a simple question but answer i don't know how to find :) lets say we have a electric motor with 1kw at 1500 rpm and that is 4.75 N.m when the electric motor is connected to worm gearbox n proportion 10:1 then the speed on output point of the gearbox will be 150 RPM. But this mean...
  7. D

    Acceleration forces acting on an elliptical mirror

    Hi all, I need to bond the back surface of an elliptical mirror (75mm major diameter and 37.5mm minor diameter) onto a voice-coil actuated mirror mount that is going to be operating at 500 Hz and has an adjustment range of +-1.5 degrees. I need to determine the g-force likely to be acting on...
  8. D

    How Do You Calculate Static Forces in a Trebuchet's Throwing Arm?

    Homework Statement The goal is to calculate the static forces in the throwing arm of the trebuchet when it's pinned as shown in the image. The counterweight is equal to 1435 Newtons. The mass of the arm is equal to 114 Newtons. Dimensions are shown in inches. The pin is in double shear...
  9. Logic hunter

    Calculating the pressure on a surface exerted by opposing forces?

    Suppose there is a circle with area 'A' and on one of the faces of the circle a force of 100N is applied and on the other face a 30N force is applied (since all 2D surfaces have 2 faces) such that these forces are opposite to each other, perpendicular to the faces, and forces are equally...
  10. johnwabeck

    Looking to achieve opposing mechanical forces.

    Hi Everyone. New to the forum I am attempting to design a piece of furniture that has opposing forces. A set of opposing stairs that either lower or raise a central platform. The idea is that two people would have to collaborate together to make sure the central platform doesn't sink. Think...
  11. Akash47

    How to Calculate Tension Forces in a System?

    Homework Statement Find the tension in each section of string in terms of ##θ_1##,m and g. Homework Equations Equilibrium of force,dimensional analysis of force. The Attempt at a Solution The support points are at rest and in each points,there are two equal tension force acting in opposite...
  12. some4544

    I Force required to tip an object

    So I need to find equations for the force required to tip over a cylindrical object. This is fairly straight forward in the case when the force is applied above the centre of mass, by taking moments about the pivot corner. However, in the case where the force is applied below the centre of mass...
  13. T

    Forces - Space Shuttle Takeoff Calculations

    Homework Statement [/B] The total mass of a space shuttle and its launch vehicle is M=2000t. a) What must be the minimum size of the thrust force, to make the rocket move? b) The actual thrust of the rocket is F=30MN. What is its acceleration in the beginning? c) Assume that a mass of a...
  14. P

    Chemistry Do ionic compounds have intermolecular forces?

    Homework Statement Do ionic compounds such as NaCl and K2O have intermolecular forces? 2. The attempt at a solution I got stuck conceptually. NaCl and K2O are ionic compounds. Their basic unit is formula units. They are not molecular compounds. Ionic compounds are held together by...
  15. G

    What Forces Contribute to the Torque on a Moving Robot?

    Homework Statement 2. Homework Equations [/B] So I basically have to establish the non linear differential equation that governs the movement of this robot (relates d and theta): The Attempt at a Solution So I know that we should have the sum of torques equal to...
  16. S

    Calculating tensions and acceleration

    Homework Statement A mass M1 is sliding across a table with coefficient of kinetic friction μk. A string is tied to this mass and runs over a pulley, drops vertically and is tied to another mass M2 which is falling. The pulley is connected to the table by a support. The pulley is a solid...
  17. M

    Can 3 forces of 9N, 4N, and 6N be in equilibrium?

    Homework Statement A mass of 3kg is acted upon by three forces of 4.0 N, 6.0N, and 9.0N and is in equilibrium. The 9N force is suddenly removed. Determine the acceleration of the mass. Homework Equations F=ma. The Attempt at a Solution My main problem with this question is that I cannot think...
  18. thebosonbreaker

    Resolving forces: Mass on a string

    Homework Statement A mass of 50 grams hangs in equilibrium on a string. The mass is pulled aside and upwards by a force of 0.3N which makes an angle of 30° with the horizontal. Find the angle that the string makes with the vertical and the tension in the string. Homework Equations Body is in...
  19. jra12222

    Auto/Motor Calculating Minimum Motor Torque for a PVC Pipe Feeder System

    Hi, I am trying to 'size' my first motor to drive a system. I am trying to make a feeder where a PVC pipe is fed as shown. There are 2 vertical rollers, on connected to the motor as shown and an other coupled to a pneumatic piston to keep the pipe under pressure. the frictional force will be...
  20. F

    I Tug of War: Does Force Matter for Winning?

    Hello, In the game of tug of war, the team that wins is the one that exerts the largest force and pulls the other team their way. However, a team can win only if the force they produce is matched by the static friction between the floor and their feet, correct? But what would happen if the...
  21. cookiemnstr510510

    Magnetic Forces on infinite current-carrying wires

    Homework Statement A) Three infinite, current-carrying wires are arranged as shown below. In terms of the given quantities, determine the magnitude and direction of the magnetic force per length acting upon wire 2. (Part A.jpg attached) B) Three infinite, current-carrying wires are arranged as...
  22. lyn83716

    What will the FBD of 2 blocks being pulled look like?

    Homework Statement Block A is on top of Block B, both are of equal mass and size. Block B is being pulled by a hook at a constant velocity. There is friction between the table and block B. Homework Equations [/B] What will each FBD look like? Is there friction between Block A and Block B...
  23. cookiemnstr510510

    Forces of a straight wire on a semi-circular wire loop (Magnetism)

    Homework Statement An ideal, infinitely long straight wire carries a current I1 and is partially surrounded by a loop of current as shown below (image attached). The loop has length L, parallel to the infinitely long wire. The loop carries current I2. A) Calculate the magnitude and direction of...
  24. Javier Lopez

    A How Are Coefficients for Nuclear Forces Derived and Validated?

    There are some theories, but I am looking for one that have proven using test data and can be placed in an excel table or a program with coefficients for some common reactions. Do anybody knows a paper with tables or formulas? I found this with a fortran code that is recent...
  25. J

    B Tidal Forces When Falling into a Black Hole

    So, if the Earth moves slowly through a large hula hoop, sensors attached on the hoop will measure some stresses, which we might call tidal forces. The faster the Earth moves relative to the hoop the larger those tidal forces are. So, if a person falls into a black hole, there are some tidal...
  26. Y

    I Thought experiment on buoyant forces on a system

    I'm a former physics student and I've been thinking about an interesting problem that eventually led me to the following thought experiment that I'm having trouble resolving. Imagine a two-compartment system, where one compartment is filled with He gas, and the other is filled with standard...
  27. maxd23

    Compression of human bone: forces

    Homework Statement While unrealistic, we will examine the forces on a leg when one falls from a height by approximating the leg as a uniform cylinder of bone with a diameter of 2.3 cm and ignoring any shear forces. Human bone can be compressed with approximately 1.7 × 10^8 N/m2 before...
  28. CheesyPeeps

    Struggling Engineering Student Needs Help with Tension in Cable Homework

    Homework Statement Homework Equations ∑MA = 0, where A is the pin. Tx = Tcos150 Ty = Tsin150 The Attempt at a Solution I've drawn in the 100kN force of the beam's weight, and identified that ∑MA = 0. I attempted to find the moment arm, but really wasn't sure how do to it, or if it would even...
  29. devilish_wit

    Short conceptual question on Work, Energy and Forces

    Homework Statement (Please check the attached image) 2. Homework Equations The Attempt at a Solution Those are my answers. I thought the magnitude of the applied force would be bigger because that would be responsible of keeping the block on that spot without having it pulled back by the...
  30. N

    Newton's Second Law: Understanding Forces, Masses, and Acceleration

    Homework Statement Two identical trucks traveling at different constant speeds are about to collide. The trucks are traveling in opposite directions with truck A going at a velocity of 3m/s right and truck B going at 4m/s left. During the collision, will the magnitude of the acceleration of...
  31. H

    Forces on an object in vertical circular motion

    Homework Statement Imagine a vertically placed clock. What forces have an effect on the object when it is in the position of 3am? Homework Equations No need od equations i guess. The Attempt at a Solution So I figured out that when the object is in the position of 12am then weight of the...
  32. YMMMA

    What are the forces acting on an object?

    Homework Statement In the attached file file. Homework Equations None The Attempt at a Solution In both cases Earth’s gravitational force always acts. For the sled, there is a force opposing the motion which can both be the frictional force between the sled and the hill and air resistance...
  33. gibberingmouther

    Momentum of a System and External Forces

    So Pearson is telling me that, basically, the ratio of internal to external forces and the briefness of the time interval is what determines whether the external forces on a system whose momentum we're studying will affect whether we can obtain a decent approximation of the momenta of the...
  34. A

    Finding Charge & Tension of a Suspended Cork Ball

    Homework Statement A charged cork ball is suspended on a light string in the presence of a uniform electric field. E=(3×10^5 N/C)i+(5×10^5 N/C)j. The ball is in equilibrium in the field. Find the charge on the ball. The acceleration due to gravity is 9.8 m/s2 . The mass of the ball is 0.7g. The...
  35. devilish_wit

    A question about contact forces and friction

    Homework Statement Two blocks of masses m1 and m2 are placed on a table in contact with each other as shown in the figure below. The coefficient of kinetic friction between the block of mass m1 and the table is μ1, and that between the block of mass m2 and the table is μ2. A horizontal force of...
  36. T

    I Gravity Propagation: How Does Time Affect Orbital Modeling?

    I was thinking about the idea of looking up at a particular minuscule spot in the sky to see a particular planet at a very precise time, say, with a telescope. I was considering how light takes a matter of minutes to reach us. But then, remembering that gravitational forces must travel through...
  37. J

    Forces on a Block and Friction on a Surface

    Homework Statement A 2.5 kg block is initially at rest on a horizontal surface. A horizontal force of magnitude 5.8 N and a vertical force are then applied to the block. The coefficients of friction for the block and surface are μs = 0.43 and μk = 0.24. (a) Determine the magnitude of the...
  38. P

    Question about resolving forces

    Homework Statement On a model ship, the mast OC has length 50 cm and weight 20 Newtons. The mast is hinged to the deck at O, so that it can rotate in the vertical plane of the ship. Small smooth rings are fixed at points A and B on the deck in this plane such that AO=OB=50 cm. Threads from C...
  39. C

    Physics rifle problem -- Forces and acceleration of the bullet

    Homework Statement A rifle bullet of mass 10g is fired and takes 2.0 ms to travel down the rifle barrel of length 0.50m with constant acceleration Calculate the muzzle velocity (bullet velocity on leaving the barrel) Calculate the acceleration in the barrel After traveling a short distance...
  40. archaic

    Maxwell's wheel and the conservation of energy

    We experimented with the Maxwell's wheel today and at the end we were asked about why does this apparatus stop since there is conservation of energy. I did some research and apparently there is a type of friction called "rolling friction", wikipedia defines it as "the force resisting the motion...
  41. I

    Electric Fields and Electric forces help

    Homework Statement This is the question Structure opposite comprises 5 ions each of which has lost one electron. The sides of the square formed by the 4 outer ions are of length 0.2nm Ion E is at the midpoint 1.What is the force on A due to ion A?Homework Equations I'd imagine: F= kq / r^2...
  42. alexi_b

    Find when the acceleration is 0

    Homework Statement A block of mass 2.42kg is accelerated across a rough surface by a rope passing over a pulley, as shown in the figure below. The tension in the rope is 13.9N, and the pulley is 12.3cm above the top of the block. The coefficient of kinetic friction is 0.395. (a: 2.28m/s^2)...
  43. alexi_b

    How far apart are the astronaut and satellite after 8.67 minutes?

    Homework Statement A 63.8kg spacewalking astronaut pushes off a 678.0kg satellite, exerting a 156.0N force for the 0.870s it takes him to straighten his arms. How far apart are the astronaut and the satellite after 8.67min? Homework EquationsThe Attempt at a Solution I tried just finding the...
  44. alexi_b

    Finding the angle in which the resultant force points

    Homework Statement Forces of 11.8N north, 19.2N east, and 15.9N south are simultaneously applied to a 3.93kg mass as it rests on an air table. What is the magnitude of its acceleration? What is the direction of the acceleration in degrees? (Take east to be 0 degrees and counterclockwise to be...
  45. vincent

    I What is it that forces an object down curved space time?

    To explain the concept of curved space time, we often use analogy of rubber sheet. If we put a heavy ball at the centre of sheet then it creates a depression and now a smaller ball will fall towards that heavy ball because of depression. But in this analogy smaller ball is falling down the slope...
  46. Physicsterian

    Effect of density on downward rolling spheres

    Homework Statement If two balls, being identical in volume, but different in density (one ball is made of iron, the other of aluminum) roll down from an inclined plane, which will reach the bottom first and which will cover a larger distance after having reached the bottom? IMPORTANT NOTE...
  47. Lukeblackhill

    I Source of Energy in a Field of Forces

    good evening! My question is the following: it is well stated that energy is conserved in any isolated system, and we can in most circumstances expand our system to a many-steps conversion of energy, but always conserved. The classic example could be the energy of the sun stored in form of...
  48. Exath

    I Why is T+f=Ma in Cylinder Roll Without Gliding?

    So I'm looking at a problem that involves a situation that looks like this the cylinder rolls without gliding. And there are these following equations that apply to it (1) mg - T = ma (for the block hanging vertically) (2) T + f = Ma (for the cylinder f = friction force, T = String force) (3)...
  49. V

    Calculating Free Body Diagram Forces

    On EngineersEdge.com they have a free body diagram of a scissor lift https://www.engineersedge.com/mechanics_machines/scissor-lift.htm Can anyone explain how the Fy, Fx components are determined? What is specifically confusing to me is how Fy is opposite in direction given the system. To me...
  50. S

    I Forces of Constraint: Solving Euler-Lagrange Equation

    Hello! I have this Lagrangian: $$L=\frac{1}{2}m\dot{r}^2(1+f'(r)^2)+\frac{1}{2}m\dot{\phi}^2r^2-mgf(r)+\lambda(\phi-\omega t)$$ This represents the motion of a point-like object of mass m along a curved wire with shape $$z=f(r)$$ The wire rotates with constant angular velocity around the z axis...
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