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. highschoolstudent454

    B Is the time derivate of force equal to the position derivative power?

    Is this wrong?
  2. K

    Force Between 2 Coaxial Current-Carrying Loops

    I have attempted to solve it as follows: Using the Biot-Savart law, I found the flux density at the centre of the smaller coil due to the bigger coil as: $$\frac{\mu_0 I b^2 N_2}{2(a^2 + b^2)^{1.5}}$$ where a is the distance to the coil (10cm), N2 is the number of loops in the larger coil (50)...
  3. dannolul

    What would the slope of the force between 2 charged particles vs 1/r^2 give me?

    I can get the slope of the line, but then I dont know what the slope is (units or whatever it is) then i get lost from there.
  4. P

    Calculate electric force using Coulomb's law (vector components are the struggle)

    So for this problem I think I am doing something weird with the trig and/or vector components. I calculated the problem like this: First drew a picture, q1 and q2 on the x axis. q3 located equidistant between them but negative .300m in the y direction. First finding magnitude of Electric...
  5. rosedog09

    Blowing Into Your Own Sail

    C. There is no net change in force, momentum, or velocity of the sail craft because the fan exerts a forward force on the air; however due to Newton's third law the air exerts an equal and opposite force on the fan. This air then exerts a forward force on the sail which cancels out the rearward...
  6. Lotto

    B What forces act on a bar when you do pull-ups?

    I am not sure here, even though it is probably simple. If you just hang on the bar and don't move up, you act on the bar with a force equal to your weight. But when you want to do a pull-up, I would intuitively say that you act on the bar with a higher force. But when I think about it I would...
  7. S

    Minimum force to tip the bin over

    I am stuck on part b) i). I understand that there is no normal force from the ground as the bin is on the point of being lifted off the ground, that is all fine. That leaves R, F and W. I know W is 40g, and I am required to calculate F, therefore it makes most sense to take moments about the...
  8. R

    B How to convert ft-lbs/sec to Newtons?

    Hi, How to convert 51065 foot pound per second to Newtons, not Newtons meter per second?
  9. tharindu_

    B Why don't cars accelerate according to F = ma?

    If the engine is constant, then the wheels of the car exerts a constant force on the floor. And F = ma, So the car should be accelerating rather than maintaining the same speed. What is going on here?
  10. WeirdUniverse

    I The answer for the total mass of the Universe?

    it requires less energy to impart acceleration to an object than to the entirety of the universe, This would break the principle of relativity since the amount of energy to move an object should be the same as the amount of energy to move the rest of the universe. This observation implies a...
  11. hello478

    Graph of viscous force and velocity

    my answer was A but i dont understand because when the viscous force equals the weight speed becomes constant but why does the viscous force needs to be equal of weight? is it weight = viscous force? or speed = viscous force?
  12. Sam Jelly

    Center of mass acceleration for an inclined plane and mass m

    Why is the center of mass acceleration zero? Did I do anything wrong?
  13. hello478

    Minimum work done to push the cube over

    my attempt: centre of mass of standing block is at 0.6 and the fallen block is at 0.25 so then change in height = 0.35 and mg = 4000 N so change in gpe = 4000* 0.35 = 1400J but wouldnt we take into account that we only have to apply force till the centre of mass is outside of the block so...
  14. cestlavie

    Why Isn't the Spring Force Sum of Both Ends?

    $$F=kx$$ $$k=\frac F x= \frac {50+50~N} {5+5~ cm}= \frac {100~N} {10~cm}= 10~N/{cm}$$ However, the answer is ##5~N/cm##, because the force on the spring is ##50~N##. I am having trouble understanding why the force isn't ##50~N## + ##50~N##. The diagram looks as though the spring is experiencing...
  15. hello478

    Horizontal force by block on a beam

  16. hello478

    Horizontal force on hinge is affected by moving the block farther away?

    my attempt: no effect
  17. I

    Centripetal force - Ferris wheel... Opposite results

    I don't understand why am I getting opposite answers. I get 250N for the lowest point and 750 for the highest point. For the highest point: ##F_{net}=F_{cp}+F_{mg}-F_N## and then ##F_N=ma_{cp}+mg = 50*(25/5)+500=750N## because I've been told that ##F_{cp}## always acts towards the center of the...
  18. Mitchell Richardson

    Finding force between solenoid and magnet

    $$\mu = 4\pi \times 10^{-7}$$ $$n = \frac{180}{0.135} = 1333.33$$ $$I = 1.85$$ $$L = 22.619$$ $$r = 0.014$$ $$F= \frac{\mu \times 1333.33 \times 1.85^{2} \times 22.619}{2 \pi \times 0.014}$$
  19. G

    I Force between opposing magnets

    Following a conversation with @Tom.G , I’ve come up with the following question, to which we’d both like an answer: Imagine two drilled magnets threaded onto a frictionless upright shaft, set N-N. One fixed down, the other floating above. Now, if I move an iron gate in and out of the gap (the...
  20. P

    Estimating the force exerted by a water jet on a flat plate - Bernoulli vs Momentum Equation

    Hi, Case 1: Imagine a steady liquid water jet with unit cross sectional area - incompressible and inviscid. density D and uniform velocity V. Operating atmospheric pressure is 0.0 Pa. The jet is in air ( no air resistance ) and hits a stationary flat plate perpendicularly. Applying momentum...
  21. M

    Does a Slowing Piano Exert More Force Than the Man Pushing It?

    Albeit the simple question, I am a bit confused on whether the correct answer choice is (B) or (C). When the piano is slowing down, shouldn't the force received by the piano be a bit greater than the force received by the man?
  22. Mohmmad Maaitah

    How Does Stress Affect a Hollow Pipe When Force Is Uniformly Applied?

    Hi, I've problem thinking about this problem isn't the force acting on "nothing"? how can there be any stress, I'm lost!
  23. mister i

    B Can the force of gravity overcome the Planck force?

    Can the force of gravity overcome the Planck force? I remember that a long time ago I read that in the universe the Planck force was the maximum force that could be reached. But when Sagittarius A and the black hole at the center of the Andomeda galaxy approach, I have made the calculation that...
  24. C

    I Work done by a non constant force over a non constant angle

    I was just wondering if I needed to set up this double integral or not. I've never seen anywhere people setting up double integrals for calculating the work.
  25. C

    Magnetic Force in Parallel Magnet Setup: Exploring the Strength of Attraction

    Imagine two parallel lines of five magnets each, spaced a few millimeters apart. In the first line, all magnets have their north poles facing one direction. In the second line, each magnet's south pole faces the corresponding north pole of the first line, but the magnets are offset by one along...
  26. S

    B Newton's 3rd Law interactions with 2nd and 1st Law Partners

    I was over on the stack but got asked to move over here. https://physics.stackexchange.com/questions/804903/newtons-3rd-law-force-on-a-rocket I've been at it all day trying to understand what partner forces are and how you can have a change in force with regard to them, or why gravity is...
  27. Juanda

    I Pushing a rod in a magnetic field

    I will present the case as an exercise because I believe it will be easier to understand that way. I didn't know if I should post it under the mechanics or electromagnetism sections because I am actually trying to link both. Since it feels like a fairly simple problem, I considered the Classical...
  28. M

    Help calculating force required to flange a cylinder

    Need help in calculating the force required to flange a cylinder outwards around the perimeter by approx. 5mm. Cylinder is either Aluminum or standard Mild Steel. Thank you.
  29. K

    Why Does the US Space Force Reference the Dark Side of the Moon?

    Dark side of the moon! I can understand that Selena Gomez I've been down the darkest alleys Saw the dark side of the moon in Wolf or Transformer movie use that phrase, But this is US Space Force, of all people! US Space Force
  30. Ineedhelpwithphysics

    Sign of Work (Negative or Positive)

    Im confused I did 850*9.8*14.7 = 1.2x10^5 Why is it not negative since the force is opposite to the motion?
  31. S

    Spinning a Bucket to measure gravity with the parabolic surface of the water

    I did (A) by balancing force on point p (in the figure). I found slope , tanθ = (w^2)x/g. I dont know what to do next. Pls help
  32. R

    B Help with science experiment magnets/force/acceleration/speed

    Sorry, I guess I should have remembered all of this from my school days, but right now I have forgotten so much that I need some help. I am developing some simple experiments for school children (age ca. 12). This one involving magnets. I am not asking for detailed calculations, that is way...
  33. MatinSAR

    Find force as a function of position: F=F(x) using v=v(t)

    If we consider ##v=-3t^2## then: $$x=-t^3$$$$a=-6t$$ Using ##t=-x^{1/3}## we have : ##a=-6(-x^{1/3})=6x^{1/3}##. My answer suggust that ##F=Ax^{1/3}## but in options we have ##F=-Ax^{1/3}##. Can someone guide me where my mistake is?
  34. W

    Two masses on a slope with a connected tension force

    I derived an equation but I have no idea how I can find the mass of the unknown without the normal force in either the x or y direction
  35. chwala

    Calculate the magnitude of driving force on the car

    My approach is as follows, let ##D## be driving force and ##F## the force resisting motion, then ##D-F = 850 × 0.3## ##D = 250 + 255## ##D = 505## Also, Force parallel to the road is given by, ##F_1 = 8500 \cos 78^0 =1767.24 N## Therefore, the magnitude of Driving force is given by, ##F_1 +...
  36. S

    I Conductors and circuits for nuclear force

    Is it possible to create something like a circuit powered by the strong nuclear force rather than the electromotive force of a battery? If so, what would be examples of some conductors and resistors that could go in such a circuit?
  37. C

    Force on a charge from a nearby charged rod

    Hi! My attempt at this solution was: ∫dF = k*q*Q / 2L ∫ (1/r^2) dy and we know that r^2 = D^2 + y^2 based on the diagram. Here is where I start getting confused. I looked at a different physics forum post and the mentor gave this equation: I am mainly confused with the math. How did he end...
  38. R

    What is the y-component of the force by the floor on her during the collision?

    A previous question I got correct was: During this time interval, what is the y-component of the average net force on her? It was just 2625, and I thought question 2 would be the same answer but it wasn't. Not sure what to do.
  39. A

    I Do the plates of the capacitor exert a force on each other?

    Do the plates of the capacitor exert a force on each other due to opposite electrical charges? Consider a planet capacitor. A simple calculation shows that this force must be very large. If you are not convinced of the magnitude of the force, I will give a simple example.
  40. C

    E&M: Forces resulting from Charges at the Corners of a Cube

    My first attempt at solving: I divided up the point charges based on the radius away from point A. 1 charge was s*sqrt(3) away, 3 charges were s*sqrt(2) away, and 3 charges were s away from point A. q remained constant. Therefore, my F_total was: F_total = k * [(q^2 /...
  41. M

    Force between poles of two magnets

    The Biot-Savart law gives us the magnetic field created by an electric current. We can calculate the force exerted on a moving charge by this magnetic field using Lorentz's force formula. But my textbook doesn't address the repulsive or attractive force between like or unlike poles...
  42. Quantum Psi Inverted

    Balancing Torques and Forces on this Beam

    In the given solution, it states that F_3f(a)=F_2f(a+b) is a "reasonable assumption". However, I don't see how we can just assume that. I can very clearly see that F_i for i=1,2,3 is likely proportional to a and b in some kind of way, but I can not clearly establish a line of reasoning for this...
  43. R

    I Advice regarding sled experiment

    Hello. I would like to design an experiment where different sled designs are compared. Specifically, I would like to asses how sled design affects the amount of force required to pull a sled over 100 meters. Any suggestions you might have would be greatly appreciated.
  44. K

    I Unit Conversions of Force: How to Convert Between Different Units of Force?

    Hello. Im studying for an exam and came across this simple unit conversion question but I haven't done something like this in a long time! I understand the conversions of each unit individually but get a bit stuck combining them. This is the question: A force of 100 N is exerted on an object...
  45. M

    B The Force of protons and quarks?

    How much force will it required to pull a quark out of a proton, and how much for to pull a proton out of a atom ?
  46. MantisShrimp

    How much force can a truck seat back cushion absorb during a collision?

    I do not know much about this, please help. My truck seat back cushion is 2" thick. Truck A is ~5,700 lbs from google. 2011 f-150 super cab 6.5ft bed. Truck B is ~5775. 2015 GMC Yukon xl slt. If truck A is stopped and braked and truck B hits truck A going 45-55mph creating a force of...
  47. Lotto

    Why can we move the spring with constant speed when we apply a force?

    One solution is that if we move with the same velocity as the spring does, the initial velocity of the block will be ##v## and the final will be zero, so its kinetic energy will transform into a potential energy of the spring. I would also say that we can say that if we pull the spring, we...
  48. nafisanazlee

    Minimum force required to keep two blocks from not falling

  49. L

    Confused about resolving Tension and Weight

    Calculations with 1: T1sintheta + T2sintheta = W T1costheta = T2costheta Calculations with 2: Wsintheta = T1 Wcostheta = T2 These are not equivalent. Can someone point out the flaw in my logic? Edit: System is in equilibrium!
  50. biomajor

    Would one be pushing as much as their weight?

    Because one is effectively pushing in the same way as a chest press machine, wouldn't the work done be the same?
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