Force 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. 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...
  2. 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...
  3. Aaron Mac

    Engineering Robotic arm- Moment/bending moment/clamping force

  4. 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...
  5. 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
  6. 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...
  7. 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?
  8. 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...
  9. 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"
  10. 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...
  11. 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
  12. 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...
  13. 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...
  14. M

    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!
  15. 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...
  16. 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...
  17. 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?
  18. M

    Centrifugal and inertial force in centrifuge

  19. 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...
  20. 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 -...
  21. M

    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!
  22. 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...
  23. 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?
  24. 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?
  25. 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?
  26. 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 -...
  27. 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...
  28. 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...
  29. 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...
  30. 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...
  31. tallwallyb

    Why Does Hooke's Law Seem Contradictory in Calculating Spring Energy?

    On the energy part, I keep getting mg=(1/2)*x*k, which is contradictory to Hooke's law F=mg=kx. What is going on?
  32. D

    B Greater momentum on impact means greater force?

    Sorry for this beginner's question, but...if F=ma, then force is all about acceleration. But if vehicle A moving at constant velocity V hits a wall, and vehicle B moving at constant velocity greater than V hits the wall, then B hits the wall with greater momentum than A and does greater damage...
  33. hagopbul

    I Asking about something that I read on electromagnetic force

    Hello All: read a paper related to electromagnetic force and its applications in acceleration of charges particles , some thing came up in it , they drive a force applied on the particle called Faraday force = [1/2B]* [dB/dt]*m*v B magnetic field , m mass of the particle , v the velocity of...
  34. nataelp

    Force between 2 point charges in VECTOR format (x i + y j + z k)

    I tried using the distance between r2 and r1 and plugging them into the equation for i, j, k. >> So for the force in the x direction it was k*(4E-6*4E-6)/(4-9)^2. The answer I got was wrong according to webassign. Can someone please tell me what I am missing?
  35. S

    I Exploring the Potential of Vacuum Energy & Gravity

    I was reading this, but am confused: https://nautil.us/the-remarkable-emptiness-of-existence-256323/
  36. S

    Determine the point of application of a resultant force

    I am struggling with part b of the question attached in the screenshot. For part a, I simply add the components of the given forces. I tried calculating the moments using vector cross multiplication, but I don't know what to do after that or even if that step is useful.
  37. C

    Need help determine force from cylinder linkage

    How can I determine the downward force of the rod with the given cylinder pressure and mechanical linkage? Do I sum my moments about the pivot? I calculated M=950xCOS(75.732)x7.81 + (X)SIN(63.414)x9.4 which resulted in 1828lbs. I get 217 lbs which does not seem right.
  38. DarkEnergy890

    Force on a Cyclist: Net Force Calculation

    My understanding is that the Net Force = Force Applied + Frictional Force. The net force is F=ma, so net force = 576N. Now 576N=450N + Frictional force, so frictional force has to be 126N. My confusion is this: 1. Force is a vector, and the frictional force opposes the direction of motion...
  39. S

    The FBD Mystery: Why Isn't Normal Force Along Radial Line?

    so this is what the FBD is.... but to be fair, to me this one looks as if the normal force in the direction of the radial line, yet it isn't???? here in the solution, it's not along the radial line, whys that???
  40. S

    Angle between normal force and radial line for cylindrical coordinates

    so I was wondering. there is this normal force on the can from the path. And there's this formula to find the angle between the radial line and the tangent or also between the normal force and either the radial or theta axis. the formula is ##\psi = r/dr/d\theta##. The thing is that here they...
  41. haha0p1

    How do I find the work done for a 100 N downward force?

    I have found the work done for 100 N, 70 N and 30 N force, but I don't know how to find work for 100 N force that is acting downwards. Force 70N: W=F×d = 70 ×0=0 Nm (Force is perpendicular to the distance moved) 100 N force: W=F×d=100×0.5=50 Nm 30N force: 30×-.5= -15Nm. Please check whether...
  42. abdulbadii

    Force to smooth a 1 mm surface bump out of a steel of sheet

    Roughly, how much force does it take to make 1 mm surface bump of diameter 16 mm circle area out of 1 mm thick steel plate of far larger area (e.g. a muscled hand pounding it laid over the base with 16 mm dia. hole by M16 bolt medium is viable enough) ?
  43. Flannel

    Force Field Experiments: Realistic Physics Questions

    Hello everyone! Events in my current webnovel have reached the limit of confidence in my physics reasoning, so I'm here to ask for confirmation of my estimates of what would happen from experimentation with force fields. While the setting is fantasy/magic based rather than superscience, I still...
  44. T

    Total force from air spring model (double acting piston)

    Hi everyone, I'm an electrical engineer working on making a linear model for a power take-off system. I've gotten inertial, friction, and hydraulic/electric components done, but what is really confusing me is the gas system; I haven't taken ANY thermodynamics. To simplify it, it is modeled as a...
  45. bphillips921

    Trying to determine linear actuator force needed

    I'm designing a pivot lift system to lift my movie projector up when not in use. I've designed the parts and begun 3D printing, but am concerned that the 3D print won't be strong enough, so I may bite the bullet and have the parts CNC machined. If I do that I want to be certain that I have the...
  46. String theory guy

    Average force when a bouncy ball collides with surface

    What have mistakes/wrong assumption have I made in solving this question? I tried to solve the problem this way N.B. I assume that the j hat direction is up.
  47. anuragchakraborty181

    The Difference in Paths: Exploring Central Force & Gravity

    When we throw a ball in a projectile motion, the ball follows a parabolic path due to gravity. And we see that earth moves in an elliptical path around the sun due the same force of gravity. So why two paths are different due to the same force? Explain using the idea of central force
  48. Quietrabbit

    Maximizing Weight Capacity for Casters on Carpeted Surfaces

    Currently I have 6 casters with a 90lb capacity, but I need this “table” (closest description to the shape) to hold over 500lbs. If I double up the wheels on the “legs” will that increase the weight capacity?
  49. L

    Impact force of model rocket with parachute

    I just launched a 2.2kg model rocket that stands about 5 feet tall and has a airframe that is 4 inches in diameter. I am trying to find how much the impact force is when the rocket hits the ground at 16MPH. Whats the best approach? Momentum? KE? or something else:) thanks
  50. K

    Engineering Hydrodynamic force on hinged flap gate

    I have attempted to use the law of conservation of momentum. The Areas are the lengths marked with the red striped line times the length into the paper, and the Forces F1 and F_hydro are the hydrostatic pressure and hydrodynamic forces respectively (acting on the plate) (The x y components is...
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