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.

View More On Wikipedia.org
Recent contents Top users
  1. K

    What is the normal force in A and B?

    A welded square frame consisting of four equal rods each with mass m and length 2l can move in the vertical plane by means of two small wheels in A and B that move without friction along a horizontal and vertical track, respectively. The disc is released from rest in a position where the sides...
  2. A

    Find the attractive force of gravity between two objects

    Homework Statement: Henry Cavendish succeeded in measuring the value of the constant "G" way back in the late 1700s. His method was to put two known masses at a known distance and measure the attractive force between them; then he could use Newton's Law of Universal Gravitation to find "G"...
  3. NathanRB

    Which force acts perpendicular to the side faces of an axe head?

    Say that these pictures are accurate. Personally, I think I can solve this problem, but the issue is, that I had a debate on it with my Physics teacher. This is how my teacher would solve it; my teacher says that each Fk on each side is constructed from half of F and Fx. So, F = 2 * Fk * sin...
  4. Like Tony Stark

    Find the force needed for a body on an inclined plane to be static?

    Here, I have two doubts 1) if the surfaces are frictionless, then there's no force being applied on the ##x' axis## of ##m_1## except from the weight, so it should be sliding, shouldn't it? So, there's no force that I could apply to ##m_2## to keep ##m_1## in equilibrium since any force that I...
  5. S

    Coriolis force caused by tangential velocity

    From another recent thread I learned that you see a Coriolis force if an object in a rotating reference frame moves along a tangent at some velocity v. (I was already familiar with the case where the velocity is radial). I still find it a little counter-intuitive that the force has the same...
  6. M

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

    Which could be the first step to find the V(t) ?
  7. E

    The force required to move an object (piano)

  8. Y

    Breaking down cellulose using impact force

    Generic biomass such as leaves contain a large amount of total carbohydrates, mostly in the form of cellulose. Some animals such as apes and can digest cellulose and that is how they can survive on leaves. Humans cannot digest cellulose because we lack the enzymes necessary to decompose...
  9. Newby

    Calculate the quadriceps muscle force

    Hi guys, I'm new here. So I have this biomechanics module which is completely out of my league (it's compulsory but it's not what I want to do). Could someone help with the following? It's about static and dynamic loads calculation. Calculate the quadriceps muscle force applied through the...
  10. C

    What type of diagram should be drawn when applying Newton's second law?

    Honestly I have no idea how to solve this. Can anyone help?
  11. E

    Work done by a tangential force shouldn't be zero

    Applying the dot product to the position vector and force vectors yields the result that the force vector is always at 90 degrees to the position vector, namely that it is directed tangentially. The mark scheme gives the work done as 0, however I don't agree. I believe they got this by finding...
  12. S

    Gravitation (planetary motion)

    Homework Statement: The particle is moving in circular orbit such a way that the net force (F) is always towards the point p (point p is on the circumference of circle). Find the variation of force F with respect to r. i.e find the value of n in the expression F=kr^n Homework Equations: F=kr^n...
  13. T

    Calculating the number of electrons given the force of repulsion

    Homework Statement: Two small spheres spaced 20.0 cm apart have equal charge. How many excess electrons must be present on each sphere if the magnitude of the force of repulsion between them is 3.33×10^−21N? Homework Equations: Charge of an electron e=-1.6X10^-19 C F=kq/(r^2) For this I set...
  14. Universeer

    Lorentz force between two moving charges

    Two charges are moving mutually perpendicular to each other in space with constant velocities. The moment one charge crosses over the line of path of second charge the force on 1st charge (located just behind the 2nd charge moving away from it) appear to be zero (Magnetic field due to 2nd...
  15. S

    Solving for weight and mass in kg in an elevator

    Fn= normal force W=mg W=(65)(9.8)= 637N Fn-637= -(65)(0.2*9.8) Fn= 509.6N I got the weight of the woman in the elevator, but I have trouble finding what the scale reads in kg. I was given the solution which read: a = (g-0.2g)= 0.8g W= 0.8g*509.6N= 52kg. My questions 1. why do I have to...
  16. M

    The direction of the tangential force (Fully developed laminar flow in a pipe)

  17. Meruem

    Force Needed to Push Bodies in Space: 100kg vs 1kg Mass

    Do we need more force to push a body with 100kg mass than of 1kg mass in space(in vacuum)?
  18. Meruem

    B Is quantum entanglement a four dimensional force?

    Why two bodies are related with each other despite the distance between them. It is unbelievable that entanglement exist regardless of any distance. Why on universe are so deeply connected with each other where distance does not play any role for the phenomena?
  19. M

    Undergraduate physics: Body flows inside liquid [ v(x)=? and V(lim)=? ]

    Homework Statement: Object inside liquid Homework Equations: T=k*v^2 F=m*a We hold an object with a mass (m) inside a liquid. On t=0 we free the object. Except the weight there is another one force, the friction of the liquid, witch is T=k*v^2 ( v=instant speed, and k=constant > 0). Also...
  20. D

    Electromotive force induced in a conducting rod

    i don't understand why in the solution of this exercise, the induced electromotive force / current is counterclockwise. Shouldn't it be clockwise? ##emf=-\frac {d \Phi_B} {dt} ## According to the picture the rod is moving upward, the magnetic flux (entering the page) is decreasing due to a...
  21. K

    How does force change momentum?

    Let's say we are in outer space.Suppose I have 2 metallic balls A and B with initial velocity 0 and same mass M and a baseball bat.Let's say I hit the ball A with force F and ball B with F' in such a way that F>F'.Ball A attain final velocity V in time T and ball B attain final velocity V' in...
  22. Snarlie

    Force & Torque on Electric Dipole in Magnetic Field

    Would this also be correct? Or is there something wrong with it? I appreciate all your responses! Snarlie
  23. FQVBSina

    Question about net work and displacement

    I know that by physics definition if displacement is zero, work is zero. However, if I push an object 5 m to the east, and then move to the other side of the object and push it 5 m back to the west. I think in this case I have always done positive work on the object and hence the total work...
  24. M

    Question on Calculating Coulomb force in VECTOR FORM

    The only thing tripping me up here is that the answer needs to be in vector form. If the question was asking for the scalar form, then I would just find the distance between the charges (plot the charges according to their vector coordinates, then use pythagorean theorem to find the distance...
  25. J

    I Can we increase an object's gravitational force by adding energy?

    like a shot bullet or arrow has negligibly more gravitational force than a still bullet or arrow?, this is what I'm asking, m=e/c^2 F=Gm/r^2, thus, F=Ge/(c^2*r^2) where e represents the (mass of the object + energy added to the object) thus more the energy, more the gravitational force, even...
  26. J

    How to find work via Force and Time

    So I can across this question in class and there were a multitude of answers, such as 0 work (J), my answer was 8100J based on the fact it doesn't tell you any distance moved, just that its 45N for 3 minutes, so my logic was 45N per second so 45*3(60)=8100J
  27. colcol500

    Net force on a Submarine Window?

    I have no idea, I honestly thought that the net force would be zero since the submarine window isn't moving...yikes
  28. vivek_salman

    Shearing / Cutting Force - Rubber bale

    I have been assigned by my tutor to design a hydraulic guillotine (rubber bale cutter). After designing its features of the hydraulic, cutting blade etc. I tried to calculate the force needed of cutting a piece of Rubber bale (Natural as reference) having an ultimate tensile strength of 30 MPa...
  29. N

    Formula to calculate the pull force between a magnet and a steel plate

    i have a neobydium magnet of grade n40 , the diameter of magnet is 15mm and thickness is 10 mm , now i want to calculate the pull force between this magnet and a steel plate when there is no gap between them ; & in second case i want to calculate the pull force when i put a 0.15mm copper plate...
  30. S

    I Attractive van der Waals force between similar atoms/molecules

    When two atoms or molecules are brought within hailing distance of each other, their average internal charge distributions get modified because the electrons' state in molecule A is now a function of the field coming from molecule B, and vice versa. If, on an average, the electron distributions...
  31. patricio ramos

    Engineering Pressure Force on a partially submerged surface

    Once I get the pressure, do I have to multiply times de area that is submerged (in this case it would be 25m^2), or do I take the whole area of the plate, including the part that is not submerged (in this case it would be 30 m^2) Thanks
  32. L

    Need help with a force calculation (deformation of a cylinder)

    Trying to calculate the force required to deform a cross section of a solid cylinder. To create an image, imagine a cylinder laying on a flat surface, and then a section of it defined as a length of X, being subjected to a compressive load. I'm trying to find the correct formula for this. Any...
  33. warhammer

    Classical Physics & Particle Motion Under Force Field

    The particle is moving under a force field with the potential energy equation described above. I find it logical that Newton's Laws can be used as in the question itself it is stated that the velocity is quite small and we could approximate its subsequent motion via the notions of Classical...
  34. H

    B Understanding Gravity: Exploring Its Nature and Role in Fundamental Forces

    Gravity can be described not as a force but a curvature of spacetime. I assume this can’t be done to the other 3 fundamental forces. If so, then we cannot treat gravity in a way similar to the other forces. Why then does QFT postulate the existence of gravitons? Why does it attempt to treat...
  35. F

    Calculating Net Force of Particle 5: A Problem Overview

    I have the following problem: So, I know the following: ##q_1 = -e## ##q_2 = -e## ##q_4 = -e## ##q_5 = e## ##e = 1.6*10^{-19}## ##k = 9*10^{9}## Now, I can get the current ##F_{net}## of particle 5 with this information: ##F_{net} = (F_{3} - F_{1})\hat i + (F_{2} + F_{4})\hat j## ##F_{1} = k...
  36. 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...
  37. A

    B The Strong Nuclear Force: Is my understanding correct?

    The strong nuclear force is the strongest of the four basic forces in nature (the others are: the electromagnetic force, gravity, and the weak nuclear force). But it also has the shortest range, meaning that nucleons (protons & neutrons) must be extremely close (~1 fm) before its effects are...
  38. A

    B Coulomb Force: Is my understanding correct?

    In a bound state like atom nucleus (except H-1), protons carry a positive charge so repel each other by the Coulomb force. This type of electromagnetic force, (also referred to as electrostatic repulsion) is an inverse-square force (has infinite range characteristics), so a proton added to a...
  39. Kaitlynn Robicheaux

    How Do I find Force when only Distance and Mass are given?

    I'm doing a lab for physics where I attach different weights to a spring and to measure different types of potential energy. I have already successfully completed the experiment using the virtual lab in the link below. I did three different trials using weights of 50, 100, and 250 grams. I...
  40. Shashwat02

    B Normal force of a body over a circular bridge

    I am not able to understand why normal force on top in a vertical circular motion the least. Also please help me with normal force of a body over convex and concave bridges. Why do we get these equations: N=mg-mv2/r (convex bridge) N=mg+mv2/r (concave bridge)
  41. A

    What slows an object during collision, force or loss of energy?

    I have an example from my machinery handbook which shows the kinetic energy of a pile driver and shows it will drive a pile some distance at a force until the energy is expended. The formula is (Average force of blow times distance)= Weight of object (driver) times distance it falls) Just...
  42. F

    Which force is responsible for light's reflection in a surface?

    I think I understand how electromagnetic force works, so I predict that if I take a big, big, long flat table, charge that table with a big negative electric voltage (say -500kV), then I shoot an electron at that table at an angle, then the electron will be repulsed by the charge, will make a...
  43. James Nilsen-Misra

    Force to propel a sliding gate up a 2,4 degree incline?

    Figure A It slopes up from Left to Right (0.205911m Rise /4,8m run=4.28%)]
  44. mgkii

    Entropic Force - Heat Transfer Mechanism

    Is anyone able to explain something to do with entropic force at a level I might be able to understand please! Ok... you need to know what level I'm at? Formal Maths & Physics at high school (I'm 50, so distant past :-) Informal Maths & Physics - lifelong interest. Consume a lot of youtube...
  45. harsh22902

    Understanding Induced Charges in an External Field

    Could'nt solve it
  46. T

    I How to Calculate the force to push a wheelchair up a ramp?

    How do I calculate the required push force (in kgf) for pushing a wheelchair up a ramp? - the ramp has a 5 degree incline - the weight of the chair and person in it totals 96.8 kg - the wheelchair has 4 wheels, all of equal diameter (15 cm) - the wheels on the wheelchair have a rolling...
  47. jisbon

    Calculating Density Using Upthrust and Drag Force in Water

    So using FBD, I came out with: since it reaches terminal velocity, I can assume F=0, thus mg = upthrust +drag So my density = mg - drag force/g * volume However the answer seems to be wrong from the answer key I was given. Any ideas why? Thanks
  48. bob012345

    Does matter exert a Force on Fields (or Light)?

    In a simple example of two current carrying wires, there are mutual forces. Do we speak of the forces on each wire as action-reaction or as someone I'm debating with, each wire and the fields from the other wire as action-reaction? Or both? Thanks.
  49. bob012345

    I Force on Photon? Interaction with Matter Explained

    When photon interact with matter there is a force. Do we speak in terms of Newtonian action-reaction? When a photon exerts a force on matter -an action- do we speak of a force on the photon - a reaction? Thanks.
  50. E

    Why have a feed force in the cutting process?

    You knew there is a cutting force in the orthogonal process, it is exerted by cutting speed, buy why have a feed force?
Back
Top