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. A

    I Force Generated By Leg Muscles in Free Body Diagrams

    Suppose a person is walking on the ground without slipping. For the free body diagram of just the person, only the frictional force is drawn in the horizontal direction. The force exerted by the leg muscles to generate a force against the ground is considered an internal force. What would be the...
  2. confused_steve

    I Force Required for Gas Struts on 1972 VW T2 Danbury Pop top campervan?

    Hi all, i'm the proud owner of a 1972 VW T2 Danbury Pop top campervan. Out of the factory these were fitted with 4 x long spring loaded struts which (when new) provided some lifting power to pop the roof up. Mine are now 50 years old and provide no assistance lifting / holding the roof in...
  3. M

    Horizontal force on a horizontal bar

    Tnet = 0 = Tcord-Twall-Tmass TLsinθ-2m(3/4L)-m(1/2)L TLsinθ= -(3/2)mL-(1/2)mL T=m/sinθ T= (1.52)/sin(39.7) = 2.38N
  4. D

    Why is Gravitational Force Proportional to Mass Product?

    why is that the gravitational force proportional to product of masses why not sum of masses or something else .........
  5. L

    B How do I calculate the drop force on a cord and eye bolt?

    i have a question. I have set up an expierment and need some values. I have a round, 3d printed disk, 0.25 inches thick and 4 inches in diameter. In the center, i have a eye-bolt attached. I have hooked up a chain to the eyebolt and some weight to the chain. I have 40Lbs hanging right now and...
  6. G

    I Moment of inertia and contact force

    Two rotating cylinders are held in contact by a force F1. The force is applied through the center of one of the cylinders. One cylinder is the driving cylinder and the other is the driven cylinder . Does the moment of inertia of the system depends on the force contact force F1? Why? And...
  7. sHatDowN

    Determine the moment of the force about point O

    There are components of 500N: 500cos(45)= 353.55 500sin(45)= 353.55 Radius is 3 then M = (353.55*5.12) - (353.55*2.12) = 1060.65is that correct?
  8. salamikorv

    Given force, need to determine what bearing to use for a crane

    Hey! I want to determine what bearings to use for this manual crane and the only thing i know is that it should be able to lift a wieght of 1000kg at max and that the winch should pull 1.24 m of cable/min. Im looking to find the force P to then determine C, and i think P is only the radial force...
  9. S

    My Mistake? Understanding Friction Force & Work Done on Snowy & Icy Surfaces

    The answer is (D), but I don't understand why. Option (A) is wrong because the work done = 0. Then, I divide the motion into 3 parts: 1) motion on snowy surface Since the sledge is being pulled horizontally (let assume to the right), there will be tension force T to the right and friction...
  10. Gixer1127

    How Do You Calculate Tractive Force for Accelerating a Car?

    Hello all, This is my first post so please be gentle with me.. I'm trying to work my way through some tricky questions so will post them below and see if anyone can give me some pointers. The questions are: A car weighs 1305kgs and accelerates from 0 to 160km/h in 4.2s. The first question asked...
  11. S

    Magnetic field force between two perpendicular wires

    There are a couple of problems with the same setup. On plugging in the values and solving for the integral, I am not getting the expected values of the force. Is there something wrong in the solution attached?
  12. Altoid

    Why does the logic of negative acceleration not always indicate negative work?

    Knowing that negative work occurs when the force applied to an object opposes the direction of displacement, and that the direction of acceleration vector should align with the force vector, I assumed the correct answer was that the indication of negative work comes from negative acceleration...
  13. ruivocanadense

    I Covalent Bonds -- Which type of force?

    When you study physics deeper you learn there are 4 types of atomic forces that represent all other in the atomic level (i.e. electromagnetic force, gravitational force, strong nuclear force, weak nuclear force). I always try to see how they manifest in the the atomic interactions. For example...
  14. C

    Force required to strip threads

    Not homework and I'm not a Mech Eng. I was trying to follow a discussion elsewhere about a building foundation that involved 2.75" diameter steel bolts. Two nuts are locked together on the bolt and embedded in concrete. Threads of the bolt itself are sleeved so only the nuts are anchored into...
  15. brochesspro

    I Meaning of the terms in the formula of the net external force

    The mathematical representation of the net external force on a system(obtained from Newton's second law) is ##\vec F_{net} = \frac {d\vec P}{dt}##, which is the rate of change of linear momentum of the system. If we substitute ##\vec P = m\vec v## into the formula for force and differentiate, we...
  16. monsterhart

    1D Particle & Energy w/ F(x): Am I doing this right?

    A) I just did what it said to do: $$\sin\left(4x_{1}\right)=1\implies x_{1}=\frac{\arcsin\left(1\right)}{4}\ m=\frac{\pi}{8}\ m\approx 0.392699081699\ m$$ B) I modified the method from an example from the lecture the other week: $$U\left(x\right)=-\int...
  17. U

    I Question on the Lorentz force: Why is the force not F=q(v×B) = F=qv×qB

    Background: is the equation of Lorentz force for the force acting on a moving charge in electric and magnetic field. For the magnetic field only it is : F=qv×B. Question: For magnetic field only why is the force not F=q(v×B) = F=qv×qB
  18. C

    Finding downward force on immersed object

    For this task, we are meant to immerse objects (held by a mesh) in water to measure the buoyant force and deduce the object densities. We can measure the weight force of the object, ##F_g##, and tension T and buoyancy force. We need to find the downward force on the immersed object, ##F_i##...
  19. Parziter

    Solar System Forces -- Simulating the planetary orbits for my project

    TL;DR Summary: Solar sytem forces on Unity Hello ! For my last year in my school, I've got a project to do, and I wanted to recreate the Solar system with forces on Unity. My forces are Velocity and Acceleration (I'm using the Frenet's formulas). I'm sorry I'm not a physicist and that's why...
  20. M

    Moments of force on Jenga tower

    M= F x d at layer 7, layers 8 - 12 has its centre of mass at middle of layer 10, which is where the weight of these layers would be acting. Not sure hoe to determine whether it would topple
  21. V

    Force between point charges at the center of two spherical shells

    If these point charges were placed in vacuum without any spherical shells in the picture, then the force between these charges would be ##F =\dfrac { k q_1 q_2} {d^2}##. But, I am unable to reason how spherical shells would alter the force between them. I do know that if charges were on the...
  22. Sagittarius A-Star

    I Why Must Pure Force Depend on 4-Velocity?

    Disclaimer: Please read in the following formulas ##E/c^2## instead of ##m##, because W. Rindler used relativistic mass, what might be confusing with today's usage of the term "mass". I am reading the chapter "38. The formal structure of Maxwell's theory" in Wolfgang Rinder's book "Introduction...
  23. Aaron Mac

    Engineering Robotic arm- Moment/bending moment/clamping force

  24. Kupa140

    Analyzing the Force of Two Disk Magnets on a Metal Plate

    The situation is as follows. We have two disk magnets. One is fixed on the ground, table, or surface and has the north pole facing up. Then we have a metal plate fixed on the vertical axis rod or something similar such that it can't move up or down, but only rotate horizontally with as less...
  25. sHatDowN

    Vector-Force image and resolve force

    The components of the force of 800 lb F along the non-perpendicular axes Get a, b. Also determine the image F on the axes a, b could some one help me how to resolve forces non-perpendicular.And also what is the meaning of image F one the a,b axes
  26. Remle

    Acceleration & Normal Force of a Box: 4 m/s2 & 418 N

    What is the acceleration of the box? Paper says the answer is 4 m/s2. What is the Normal force acting on the box? Paper says the answer is 418 N. I know that for most cases FN=Fg=W. So, by definition the "original" Normal force is 245.25 N (am I correct?) I calculated the Fay which is...
  27. sHatDowN

    Vector sample problem -- Force components on a spring mechanism

    Determine the amount and type (tensile or compressive) of the spring force so that the resulting force is a vertical force. Also get the resultant force. i find 60N (compressive) and resultant forces is 10800 is that correct?
  28. C

    I Calculating Force Applied to an Object of 100kg Moved 1m in 5s

    if an object of 100kg is moved or lifted to a distance of 1m taken 5s, then how can i find the amount of force applied to the object. in every problem i noticed, force value is given to find the Workdone and the Power. I think it is simple problem, but i can't find it simple. can anyone clear...
  29. sHatDowN

    Vector problem, magnitude of the force

    Member CB of the vise shown exerts on block B a force P directed along line CB. Knowing that P must have a (1237) N horizontal component, determine (a) the magnitude of the force P, (b) its vertical component i don't get it what the "N horizontal component"
  30. L

    B If gravity was a force wouldn't going back in time cause us to float?

    This might sound as a dumb and silly question but if you think about it, it makes sense. If we wrongly assume that gravity is a force just like any other, and given the fact that time is closely related to gravity and that gravitational time dilation is a thing, wouldn't reverse time travel...
  31. K

    How can I troubleshoot and verify my calculations for magnetic force?

    I am getting a wrong answer for part b, however part a and c both are correct : a. 0 N b = -2.91E-3 N (WRONG) c. 1.4E-4 N
  32. KataruZ98

    B Leg muscles’ force as a system of levers

    If I know a person has exerted total force F with their legs and I’m interested in breaking down said force in smaller forces exerted for each involved muscle group - how can I do it? With a basic level of understanding of human anatomy I can divide the leg as a series of levers but how can I...
  33. C

    I How to Calculate force exerted on a falling body?

    I'm curious about impact on falling object, so i have taken initiative to solve this problem. I considered only force on the falling object would be its weight and taken F=mg. With only limited data m=.25kg and drop height h=1m. Pondering on this consideration practically, it will have more...
  34. C

    Infinite number of pairs of Force and distance R from AoR

    For part (b), The solution is However, is there really an infinite number of pairs physically speaking? It would be very hard, say, vary the force applied by ##0.0000001N## for example. Many thanks!
  35. V

    Discontinuity in an Electric line of force

    This is a tricky and difficult question for me. I know from reading various textbooks that electric lines of force are always continuous without breaks, but cannot pinpoint a reason for this. The only reason I can come up is that an electric line of force must always begin and end on charges...
  36. D

    I Question on Hall Effect and magnetic force

    so with a Hall Voltage, you have positive current traveling upwards in a wire in the +y-direction and a magnetic field into the screen in the -z-direction. the right hand rule has positive charge deflecting to the left. now if you look at the drift velocity of electrons moving downward in the...
  37. Pushoam

    Force between the plates of a capacitor with dielectric slab inserted

    The the electric field inside decreases due to the presence of a dielectric by a factor of dielectric constant K. Hence the force between the plates will decrease. Is this right?
  38. C

    Centrifugal and inertial force in centrifuge

  39. C

    Exploring the Relationship between Buoyancy Force and Gravitational Force

    Picture below. Both bodies are made of same material but the body placed in water had 2.4 times greater mass. What is the relationship between buoyancy Force and gravitational force between body in water and body in air?I have no clue how to solve this. I know that body with greater mass has 2.4...
  40. paulimerci

    Find momentum transfer and force on the head with and without a helmet

    Without helmet, m = 4kg, ##v_f = 10m/s## ##\Delta t = 0.0005sec## $$ \Delta p = mv_f - mv_i $$ $$ \Delta p_{without} = 40 kg m/s$$ $$ Impulse_ {without} = F_{net} \cdot \Delta t$$ $$ force_{without} = 80000 N$$ With helmet m = 4kg, ##v_f = 10m/s## ##\Delta t = 0.002sec $$ \Delta p = mv_f -...
  41. C

    Driving force from buzzer for jacket of length L

    For this problem, How do we tell when the buzzer vibrates during the cycle to provide the driving force? Many thanks!
  42. enigmaticbacon

    Converting Effective Mechanical Load to Newtons (Capybara)

    Hello again! I've found the capybara's EMA to be 0.71. Their mass to be 55kg. And their average speed to be ~3.0km/h. I want to figure out how many capybaras it would take to overcome Friction * Normal force of ~125,000N. How would I go about doing that...
  43. abdulbadii

    The ideal weight or force to push a drill

    What is and how is the estimation of the ideal weight or force to push (bit being in) a driller down when drilling (stainless) steel to bore 3-9 mm hole?
  44. Pushoam

    Electric force on the charge kept at the centre of a metallic shell

    Hence the electric force on the charge in both cases is zero. Is this correct?
  45. D

    Solving for Tension in Net Force Equation: Need Help!

    I have tried finding the tension of the string through the equation Net Force = T - mg = ma but I am struggling with coming up with the correct acceleration. Is my net force equation correct?
  46. Hippo89

    Calculating Net Force of 3 Blocks in an Elevator

    m1 = 4 kg, m2 = 12 kg, m3 = 8 kg. k = 327 N/m for all three blocks. The elevator accelerates upwards at 3.8 m/s^2. Net force of block one would be equal to force applied by top spring minus weight of system, since top spring is holding all 3 blocks. F1 = 4*3.8= Fs,top - Wsystem = Fs,top -...
  47. D

    Fluid Forces in a Manometer: Understanding Pressure and Kinetic Energy

    Note: I am self-studying Material and Energy balance courses and I haven't done fluid mechanics yet. Case 1) Consider the manometer in the figure below. Levels on both sides of the manometer which are open to the atmosphere are equal. If we analyse the forces acting on the left side of the...
  48. Richard90

    Finding an Equation for Measuring Reactive Force at the Gastrocnemius

    Good morning, I’m new to the forum, thank you in advance. I’m an Italian med student based in France. I’m struggling to find an equation for a project that I am following. I should measure the reactive force at the level of the gastrocnemius (shown in the figure, red arrow). I know the force...
  49. S

    I Work done "against centrifugal force"

    Consider a merry-go-round (carousel) with a tube fixed radially on it. I use a pole to push a bowling ball slowly through the tube towards the center. (Slowly, so that the kinetic energy is negligible when the ball reaches the center. Also assume zero friction). What happens to the work that I...
  50. N

    What exactly is wrong here? (F=ma when Force and acceleration are zero)

    If F = 0 then a = 0. When the equation is written in the form F = m*a, it appears ok, that whatever the mass be, LHS and RHS of the equation are equal so no problem. But when the same equation is written in the form m = F/a, then m becomes undefined when F = 0 and a = 0. It occurs to me that...
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