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. P

    Force & Energy Changes of Air by Helicopter

    Solution 1: Force on air = Force on helicopter. ##F = \frac {dp} {dt} = v \frac {dm} {dt} = v^2 \rho A## ##P = Fv = \rho A v^3## Solution 2: Power from helicopter converted to rate of kinetic energy increase of air ##P = \frac {dE} {dt} = \frac {1} {2} v^2 \frac {dm} {dt} = \frac 1 2 \rho A...
  2. Istiak

    Why used $\cos\theta$ for $\text{y}$ axis or, gravitational force?

    >![figure 3.2](https://physics.codidact.com/uploads/B5XdWq6GbB4vwyADQdALaCrC)![figure 3.1](https://physics.codidact.com/uploads/pkmWFgoesvQaiAfv5yKj6ynB)<br/> >Mass M1 is held on a plane with inclination angle θ, and mass M2 hangs over the side. The two masses are connected by a massless string...
  3. MichPod

    I Calculating Force & Acceleration in Electrostatic Field (B=0)

    For a case of electrostatic field (B is equal zero), how should the force acting on a moving charge be calculated if we want to take into account all the relativistic effects? Also would it be correct to calculate the acceleration of the charge as a=F/m, or should some other formula be used? For...
  4. M

    Change the application pole of the moment of a force

    Good morning everyone! I am an aerospace engineering working on my thesis and i am trying to solve a little problem. In the picture you can see an "aeordynamic" body. The CFD analysis gives me the forces and the moments acting on this body. How can i calculate the momentum acting on the body...
  5. E

    B How to determine force based on pressure

    Hello In a pharmaceutical lab,a certain pressure is applied to IV bags using the equipment shown below.We need to calculate the force acting on the bags based on the applied pressure.I know the formula is F=PxA.But i am not sure what the surface area is.Should i take the whole surface area of...
  6. F

    I Questions regarding traveling speed in time and gravity as a force

    I am an Engineer, so I have some knowledge about physics and calculus. I've seen relativity in university years ago but only briefly. The majority of my knowledge in SR and GR, which isn't much, are from reading, studying and searching online myself. I have seen some definitions that I am not...
  7. Sagittarius A-Star

    I Force on Scale in Rocket Scenario: Calculation & Discussion

    [Moderator's note: Spin-off posts from previous thread have been included in this new thread. Also, the OP's re-post of the scenario for discussion has been moved to this top post for clarity.] Yes. Physically, scales measure a force (and indirectly the energy) in their frame. Consider the...
  8. N

    B Why do moving charged particles feel a force in a magnetic field?

    When I read things about magnetism on internet, I don't understand at all about one thing: If a moving particle receive a force if it's in a magnetic field, so it should accelerate, so what happen if we change the referential so that the particle now don't move? The particle shouldn't receive...
  9. S

    [Electrical force] 2 balls hanging from ceiling, angled

  10. nomadreid

    Medical Is a small tidal force on the body harmful over the long term?

    In the following page (which, despite examining a question that comes up in science fiction, raises valid scientific questions): http://pages.erau.edu/~andrewsa/sci_fi_projects_spring_2015/Project_1/Eilts_Mitchell/Enders%20Game%20Eilts/Enders%20Game%20Eilts/index_Eilts.html I encountered the...
  11. S

    [Electrical force] Electrical charge in equilateral triangle

  12. S

    [Electrical force] 2 balls hanging from ceiling

  13. R

    Force Diagrams for a Combined Mass

    I know that the ##F_{AonB} = -F_{BonA}##, but I just wanted to check something. If object A is the truck, then the x-direction should have a vector coming from the force of the engine driving the truck forward, a vector pointing in the negative direction for friction, and a vector in the...
  14. Shreya

    Force on a dipole in a non uniform electric field

    I have figured out how the force is towards left in the first case. I think it is due to the larger force on - charge. Please help me out with the second and third case.
  15. J O Linton

    B What is the distance at which gravity and the cosmological force are equal?

    In considering the excellent answers given to my previous query about a photon in a box, I was led to consider what force was needed to hold the walls of the box stationary (w.r.t. an inertial observer inside the box.). If you place a mass m on the end of a very long string of inextensible...
  16. Einstein44

    Calculating Magnetic Field Strength and Force of Eddy Currents in a Solenoid

    I have jus thought about how maybe I could sue the magnetic field strength equation for a solenoid (that I used to find the Emf in the first place) again, to find the magnetic field strength arising from the induced current: B= μNI / L where μ is the permativity of free space N= Number of...
  17. S

    Calculation of the lateral force of a trailer coupling

    Hello, i´ve got a problem with the calculation of the forces on the hitch of a vehicle and a trailer. I do need the lateral force on the hitch for the calculation of my single track model of the vehicle and trailer. I have a longitudinal model of the vehicle and the trailer. My input signal...
  18. P

    B How do I express the force of me falling 33 feet onto concrete?

    I weight 90.7kg. I fell 10.05m landing on soild concrete. how do I express the "power of my impact? in G-force? A relitive weight? I am self taught in very basic physics after a high school education.
  19. Paige_Turner

    B The Impact of Tidal Force on a Star's Magnetic Field and Supernova

    And if a star is severely stretched by tidal force, how does that affect its magnetic field and the process of it collapsing at the start of a supernova?
  20. tmalcolm

    Force pressure variance after hole is plugged?

    There is a tall cylinder filled with water. And there is a 3 in diameter hole near the bottom and water is gushing out. (assume the cylinder is continually being re-filled from the top) You work to plug the hole with a 10 inch long cylinder that is exactly the perfect diameter fit to plug the...
  21. vibha_ganji

    Halliday, Resnick & Krane Chapter 5: Force on Pulley

    As the force on a pulley is equal to twice the tension, I just have to find the tension to solve part A. To do so, I first wrote the equations for both m1 and m2. m1 * a = T - m1g m2 * a = T + N - m2g The tension must have the same values for both equations so I added both equations to find...
  22. nomadreid

    I Van der Waals attractive force: Why don't the imbalances average out?

    The summary refers, for example, to the Wikipedia explanation "The force results from a transient shift in electron density. Specifically, the electron density may temporarily shift more greatly to one side of the nucleus. This generates a transient charge to which a nearby atom can be either...
  23. P

    Trouble with FBD: Is There an Upward Force?

    I am having trouble coming up with a FBD. I know there is a Fg, Fn, friction, and applied force on the masses, but would there be another force going upwards because of the acceleration?
  24. crudux_cruo

    B Confusion while trying to build intuition of centripetal force

    As I understand it, when a body undergoes uniform circular motion its velocity does not change in magnitude but instead direction. This change in velocity, or acceleration, is directed inward towards the center of the circle. If a body was not experiencing a net centripetal acceleration, then...
  25. M

    Help with Coulomb's law: Net electrostatic force

    I tried just calculating the force with Coulomb's law, then calculating the forces for each vector individually and adding, but I got it wrong both ways
  26. A

    I How is static friction the centripetal force during a car turning?

    Hello, as you can see i am trying to understand conceptually how the tires during turning create a centripetal force. It was explained to me that as we turn the car tires, the tires similar to a ski or a wedge, now want to push the ground to the side and forward. If the ground was loose, this...
  27. E

    When an object is accelerating, does speed, velocity, or force change?

    qn3: why is statement 2 the only answer? isn't speed one of the factors in velocity too? then shouldn't statement 1 be true too?
  28. E

    Identifying which region in the conductor experiences a greater force

    I feel that its M because as the conductor moves upwards, towards K, an equal but opposite force will be produced at M to pull the conductor downwards, but answer is K.
  29. E

    Identifying which region of a conductor experiences the greater force

    I feel that its M because as the conductor moves upwards, towards K, an equal but opposite force will be produced at M to pull the conductor downwards, but answer is K.
  30. S

    I If gravity is not a force, what is holding us down?

    OK. Gravity is not a force it is a contraction or curvature of space. I was free-falling and now I hit the ground. Why don't I float through the universe, or go upward instead of still trying to go downward. Because I hit the ground, and now there is no force(like gravity) and my free-falling...
  31. AdvaitDhingra

    B Calculating Force of Ball-Spring Collision

    Let's assume I have a ball moving at a constant velocity and it collides with a spring and the spring compresses n cm. If I know how much mass the ball has and the spring constant D, how would I calculate the Force? I mean since F = dp/dt I would have to know the time in which the stopping...
  32. LucaCaiaffa

    I Motorcycle model and tire force

    I'm having issues in the application of tire forces while deriving a multi-body model of a motorcycle via Lagrange. In particular, I considered several bodies that are: swingarm, main frame, front upper fork, front lower fork and wheels. I suppose the wheels to have zero slippage, then...
  33. Nauticale

    Force from Water Entering a Pressurized Tank with No Relief Valve

    Hello all, I am trying to understand how a force at the opposite wall from water entering a pressurized air (atmospheric pressure) tank, and for this discussion it is rigid, with no relief valve to displace the compressed air can be deduced. I have created a simple illustration and believe this...
  34. akashpandey

    I Why is the definition of work = force times displacement?

    Hello everyone, I was curious about how do we define a physical quantity and mathematical relation between them. For example: Work done is defined as product of force along the displacement and displacement i.e W=Fcos(theta)d. Now this definition is given in books straightforward but my...
  35. B

    I What force is needed to collapse this spring-loaded pair of arms?

    Hello . The goal is to look for what force F I need to apply in order to return the arms to the closed position. Attached is a schema in the hope that my purpose will be understood I want to know what forces are acting on the system of the arms as well as the springs Many thanks in advance
  36. E

    I Does charging my phone increase its gravitational force?

    If the statement above is correct, I do not understand this concept. I guess by charging my phone I am not producing matter. Does it mean in this case, energy converts to mass (not matter)? Can someone please explain this?
  37. R

    Calculating Potential Energy from Force for Non-Linear Systems

    If I have a force that behaves according to the formula ##F(x)=\alpha x-\beta x^3##, how can I get the potential energy from it? I know that: $$-\frac{\mathrm{d}V(x)}{\mathrm{d}x}=F(x),$$ but what about the limits of the integration?
  38. S

    Hurricane forces — Comparing the force from a 60 mph wind to a 120 mph wind

    The marker wrote that the answer is 4 and it's because m and v double. I don't understand how m doubles??
  39. D

    Determine the forces using virtual work(unit force method)

    Summary:: Require to determine the designated forces using principle of virtual work ( unit force method ) I have no idea how to determine the multispan beam using virtual work, if I start to analyse the subsidiary portion BC member, the Yc can be calculated and following by the Ma... it seems...
  40. brotherbobby

    Force of water against a dam gate

    Question : I start by putting the image of the problem from the book. The water surface is given to run along the (top) edge of the bridge. Attempt : The crux of this problem lies in the fact that the pressure of water against the gate will vary along its depth ##h## as ##\rho gh##. This makes...
  41. barryj

    Centripetal force on a person on the Earth

    I am confused. See my diagram below. With the Earth rotating, I think the scale would read the force of gravity or 448.4 N. If the Earth were not rotating, would the scale read less or more due to the effect of centripetal force? I tend to think more by an amount of 1.78 N. Is this correct? If...
  42. Delta2

    B Gravitational force between matter and antimatter

    What is the current scientific consensus on the gravitational force between matter and antimatter. Is it repulsive, attractive or zero?
  43. H

    Force on a charge centered around a rotating magnet

    Charge will experience a rotating magnetic field around it. What will be electric field ( If any ) at the centre, generated by rotation of magnet ?
  44. A

    Force on two cables holding a liquid-filled container against a wall

    Before, sorry for my English, it is not my native language I already have the solution to the issue, I just didn't understand a step. 1) Calculation of weight force (vertical): $$ F_v = \frac{\rho \pi R^2 . L .g}{4}$$ 2) Calculation of force due to water pressure on the plate (horizontal)...
  45. M

    Question about how to calculate the Resultant Force at this point

    Hello all Trying to solve this one, faced a dilemma if i should trasfer the 5N vector from third to first quadrat becuase it head is on the 0 axis ass opposed to the two other vectors. If it remains in third quadrant its components eouls be both negative, if transferred to first quadrant both...
  46. D

    Problems about magnetic field, electromotive force, induced current

    Hi, I was practicing some problems on the magnetic field and the electromotive force, when I got stuck on these two exercises. Could you help me figure out how to proceed? In the first problem, I tried to find the magnetic field flux by multiplying the induced current for ∆t and R. Should I now...
  47. P

    Does "internal force" have 2 meanings in physics?

    My understanding is that gravitational fields produce an "internal force" (weight) on objects and hence gravity cannot change the total mechanical energy of an object. But in a free falling situation there is no other internal force cancelling it out, so it does not seem to be an internal force...
  48. T

    What is the Correct Distance with Force from Both Sides?

    I am getting distance 87.5m. Is this correct?
  49. P

    Using Lorentz Force to derive V = E/B

    Suppose the E-field is ##-E_y\hat y##, and B-field is ##B\hat z##. Mass is ##m##. z | |_____x / y ##m(\ddot x \hat x + \ddot y \hat y) = q(-E_y \hat y + (v_x \hat x + v_y \hat y) \times B \hat z)## By grouping terms with ##\hat x## and ##\hat y## together, ##m\ddot x = -qv_yB##...
  50. Vash25

    Gravitational potential energy question - normal force on us

    Hi, If we are standing on the ground, the Earth applies a force equal to our weight to us, but why do we feel a greater force when we fall to the ground from a certain height? Our weight is the same along this small height because our mass and acceleration are the same and, even so, the normal...
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