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. 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?
  2. 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...
  3. hagopbul

    I Asking about something that I read on electromagnetic force

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  4. 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?
  5. S

    I Exploring the Potential of Vacuum Energy & Gravity

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  6. 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.
  7. C

    Need help determine force from cylinder linkage

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  8. 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...
  9. S

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

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  10. S

    Angle between normal force and radial line for cylindrical coordinates

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  11. haha0p1

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

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  12. abdulbadii

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  13. Flannel

    Force Field Experiments: Realistic Physics Questions

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  14. T

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  15. bphillips921

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  16. String theory guy

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  17. anuragchakraborty181

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  18. Quietrabbit

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  19. L

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  20. K

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  21. C

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  22. R

    I Vacuum force factors (vacuum created by a "flow through" liquid)

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  23. andymag

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  24. NeedFreedom

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  25. MatinSAR

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  26. BurpHa

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  27. M

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  28. Ranku

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  29. N

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  30. Coldry

    The Force Of The Ladder Against The Wall

    OK folks, I'm sure this will be easy for the brains in this forum, but I've always been curious as to how this is done. So if you have situation where you have a ladder leaning on a wall and a person is some way up the ladder. If you know the length of the ladder (3m), the angle the ladder is...
  31. Spector989

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  32. Argonaut

    I Don't Ever Mention "Centrifugal Force" to Physicists

    I've just come across the following line while studying (Young & Freedman) and found it amusing. It sounds like a dirty family secret we discuss once and then should never mention again :biggrin:
  33. PhysicsRock

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    My approach is to use the definition of the Force with ##\displaystyle F = \frac{dp}{dt} = \dot{m} v + m \dot{v}##. Since ##m(t)## decreases linearly, I should be able to set ##m(t) = M - \Phi t##, thus ##F = - \Phi v + (M - \Phi t) \dot{v}##, which gives ##\displaystyle v = -\frac{ F - (M -...
  34. H

    Solving for 'a' with Torque, Force, and Mass Moment of Inertia

    What I did was plug in the outer radius time the force into the torque and then the mass moment of inertia is equal to m*ro^2 so then I plugged in the mass times the radius of gyration squared into I and solved for a but this is not right.
  35. Spocktastic

    What is the Correct Angle for Tension Force in Arm Mechanics?

    I already solved for part a, setting the sum of the Torques of the arms and deltoid equal to 0 and subbing in values which lead to a tension force of 870N in the deltoid. For part b, I remembered the law of static equilibrium, so the summation x and y components of all the forces in the system...
  36. paulimerci

    How much force does the 20 kg block exert on the 10 kg block?

    The contact force on 10 kg due to 20 kg is taken as Fc2 m1 = 30kg, m2 = 20kg, m3 = 10kg F_A = Applied force μ = 0.15 Net force = mass X acceleration Fc2-Friction force = m3 X a, where a = F_A / (m1 +m2+ m3). Therefore the equation becomes Fc2 = m3 F_A/(m1+m2+m3) + μN = F_A/6 +15 I...
  37. T

    Engineering Determining Force and Directions on Truss with Pulley

    So far I have used methods of joints to determine the forces at point E, D, and C. However, there is also a pulley attached to point D and E which I included in the sum of forces, but I'm not sure if that's the correct way to apply them. Every force I've calculated so far has also been in...
  38. BurpHa

    A greater force? (A train engine pulling two identical cars)

    My choice is C, which is "equal to." Here is my reasoning: The engine pulls on car 1, so car 1 is having a force acting on it, which pulls car 1 forward. Likewise, the same amount of force is applied on car 2 by car 1 by moving forward with the same amount of force from the beginning. So it is...
  39. M

    Hop height of a rod and speed/ time if hit upward with force f

    I want to make a few of these if it will not cost a lot.
  40. MatinSAR

    Is the Work Done by a Variable Force Non-Conservative?

    Can anyone tell me if my answer is wrong ?!
  41. K

    I Force required to pull a cruise liner or cargo ship

    I was wondering how much force is required to pull the Cargo ship using a Kite as shown in below image and specifications given in table? This picture is taken from a seawing aka airseas website. I do not know the water / air / skin resistance values or coefficients for the cargo. All I know...
  42. paulimerci

    For which case would the applied force be greater?

    If F is applied at an angle above the horizontal, it decreases the normal force and vice versa. So in case A, net force along X = F applied cos theta - friction since the object is moving with constant velocity, a = 0 and so the above equation becomes F applied cos theta = friction Now along...
  43. O

    Converting Force Measurement to Pressure

    I have a zip-tie like structure, which when pulled, squeezes an elastic part. Think of it like a having a zip-tie around your finger. I can measure a force that is related to the squeezing pressure. This relationship between force and pressure is quite linear. I would now need to create a...
  44. Z

    Elbow Flexion Joint Reaction Force

    Homework Statement:: This is not a homework, but I want to know how to find the joint reaction force of the 2d elbow flexion, if I know the angular acceleration of the forearm, and the mass of elbow with a known weight on hand. I assume the forearm is a simple cylinder. Suppose the angular...
  45. arhg

    A Normal force and force of friction inside a tube

    Dear all, Me and some colleagues (non-physicists) are discussing how force works when passing a cylinder (which we are holding) into a narrow tube. As we insert more of the cylinder into the tube, the force we are exerting is increasing. My theory is that the normal force is increasing and his...
  46. A

    Calculate the minimum force required

    I tried taking the components but got stuck there on what value of theta I should take
  47. G

    Analysis of a Figure to Calculate Force and Moment

    Figure: My attempt at a Solution: $$\overrightarrow{TFD}=TFD\dfrac{(-0,16\widehat{i}+0,11\widehat{j}-0,08\widehat{k})}{0,21}$$ View from above: We calculate ##D##: $$\sigma =90-\arctan \left( \dfrac{0,07}{0,240}\right)=73,74\, \textrm{º}$$ $$d=0,16\cdot \sin (\sigma)=0,1536\, \textrm{m}$$...
  48. samy4408

    I I found 2 formulas about surface tension -- which one is correct?

  49. G

    Tainter Damper Figure: Analyzing Forces

    Figure: Attempt at a solution: $$b=12\, \textrm{m},\quad H=8\, \textrm{m}$$ a) $$F_H=p_{CG}A=3767040\, \textrm{N}=\boxed{3767,04\, \textrm{kN}}$$ $$A=8\cdot 12=96\, \textrm{m}^2$$ $$p_{CG}=\rho_g h_{cg}=39240\, \textrm{Pa}$$ b) $$F_V=mg=\rho_g V$$ We calculate ##\theta \rightarrow 8=10\cdot...
  50. A

    Calculating Energy Dissipation for a Moving Object Using Integral Calculus

    Since ##F = -b * v## I said ## F(x) = -b*v(x) ## Also x(0) = 0 and x(T) = ## \frac{1}{3}aT^3 ## I made the integral ## ΔE = -b* \int\limits_0^\frac{aT^3}{3} v(x) dx ## I wanted to replace v(x) with v(t) somehow I first tried ##v(x) = ax^2## but then realized that was wrong Then I tried using...
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