What is Forces: 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. G

    Work done against resistive forces by comparing Ek and work done

    Missed units in the photo - J Answer is 110 000 J
  2. 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...
  3. G

    I Are Tidal Forces Curvature of Space?

    I've heard it and I've read* it before, so I just want to make sure I understand this so I never have to wonder about it again. So, are tidal forces exactly curvature of space? Here's why I think the answer to that is yes: .I've seen a spacetime interval equation which has a coefficient on...
  4. D

    Calculating Support Reaction Forces using Method of Joints

    Summary:: The question requires us to determine the member forces using method of joints but I couldn’t figure out how to calculate the support reaction forces I tried to use equilibrium equations to solve the question but the force applied will be canceled out, and eventually the reaction...
  5. S

    Direction of forces on a uniform catilever

    The following is my work: The following is the answer given: While I took FA as the pivot point, the answer seem to have taken FB as the pivot point, and got negative value for FB. As the result, the answer seems to have used the tensile strength for FA and compressive strength for FB...
  6. GiriBang

    Resultant of two forces in two different situations

    https://cdn.discordapp.com/attachments/843776584255406080/847500756194033754/20210527_211342.jpg
  7. R

    The attractive gravitational forces between two people separated by 1.5 meters

    F= Gm1m2/r² = 1.667*10^-7 N. I don't understand How to calculate angular velocity?
  8. P

    Understanding the Forces Behind Part B of the Graph

    I am only asking about the answer to part B, but reading through part A may give some some context/familiarity. Below is the answer to part B: I largely understand the graph except for 1 part. My understanding is as such: At first, ##x = \frac {\mu_k m g } {k}##. Force exerted by the...
  9. shk

    Predicting Landing Point on a Moving Train: Exploring Forces and Motion

    I need help with the following question please. I understand that the person carries on in straight line while is jumping. This is because there is no horizontal force acting on him so based on Newton's first law of motion he continues with the previous speed. I know he should land on A or B...
  10. jacobtwilliams001

    Intermolecular forces and Transport phenomena

    I am able to find and understand T from kinetic theory, but I do not understand how to use pressure gradient per unit of area and per unit pressure gradient.
  11. S

    How do I calculate the ratio of forces between two conducting spheres?

    Here are the answer choices: a) F1 = 2F2 b) F1 = 8F2 c) 2F1 = F2 d) F1 = 4F2 e) F1 = F2 I figured that Coulomb's law would tell us the magnitude of the forces are identical, so I answered E, but that was incorrect. (Screenshot of question attached)
  12. simplemind

    I Question about particle interactions and the forces between them

    I have read that if the exchangeparticle of an interaction has even spin then the force between them is attractive if the charge is equal (gravitation) and repulsive if the charge is not equal. Is this wright?
  13. P

    I Fictitious forces and their associated energies

    I understand the idea of a fictitious force. What I am confused about is the energy/potential associated with it. For example, if a cylinder of water is rotating, there apparently exists this centrifugal potential energy, which is obtained by integrating mrw^2 dr. Why is it that the...
  14. B

    What are the forces exerted by a wall on a hinged rod?

    I have a dilemma. If I look at the diagram and say the sum of the forces in x and y direction has to be zero, then I will simply conclude that the force of a wall on a revolvable rod is the blue N as drawn. But what if the force is actually the green N? To me, it makes more sense because if...
  15. S

    MHB Forces of 8N: Find Angle & Mass of Particle

    Two forces each of size 8N, have a resultant of 13N. a) Find the angle between the forces b) The two given forces of magnitude 8N act on a particle of mass m kg, which remains at rest on a horizontal surface with no friction. The normal contact force between the surface and the particle has...
  16. rhotonsix

    What determines the direction of static friction forces?

    My understanding of static friction is that it is a resistive force in response to an applied force. I recently read the following example. A rope of uniform density, length L, is fastened to a plane with incline angle “theta” along its length. The question asks for the tension at the top of...
  17. Pipsqueakalchemist

    Engineering Questions on Forces & Friction: Analyzing Plate & Block Motion

    So I have questions on two separate questions. The first question is about the fbd of the plate attached to the pin. How can there be an Ax since there’s no other force in the horizontal direction wouldn’t the plate start moving on the x-direction due to imbalanced forces. Second question about...
  18. V

    Forces on particle in complex motion relative to ground observer

    A table with smooth horizontal surface is fixed in a cabin that rotates with a uniform angular velocity ω in a circular path of radius R. A smooth horizontal groove AB of length L(<<R) is made on the surface of the table. The groove makes an angle θ with the radius OA of the circle in which the...
  19. bo reddude

    I Physics of exercising and forces felt

    Let's imagine an ideal scenario where you're lifting your own weight in its entirety. Let's say a woman weighing 100 lbs. Suppose she's doing an idealized handstand and pushup from that position. So she's lifting 100 lbs. Let's say ideally all of the forces are on her arms only. Do these forces...
  20. P

    Meaning of F = -dU/dx for capacitors

    I have noticed that F = -dU/dx in gravitation gives the attractive force experienced by both bodies. For capacitors, does F = -dU/dx give the force experienced by each capacitor?
  21. P

    I Does the Normal contact force act through the centre of mass?

    Consider the following situation: You have 1 rectangular block lying on a table, and an identical block is placed above the block on the table. Now, this new block is constantly pushed to the right, right before it topples off. Consider the torque about an axis passing through the rightmost...
  22. P

    I Why is my derivation of the catenary wrong?

    Important note: I only derived the differential equation, I did not solve it. What I think caused the mistake: - the tangent approximation (tan(theta+dtheta) ~ tan theta + d theta
  23. K

    I Which forces maintain the shape of the Milky Way?

    Gravity, inertia, conservation of momentum and angular momentum are some of the forces and conserved quantities that I could think of which will tend to maintain the shape of the Milky Way. How is the separation of the spiral arms maintained?
  24. L

    Circular Motion Questions (energies, forces, angular velocities, etc.)

    Question 1: I believe that the ratio would be b. 8:1 because by combining the formula for kinetic energy and momentum the expression Ek=p^2/2m can be obtained. Thus, for a body of mass 2kg with twice the momentum: Ek=2^2/2*2=1 For a body of mass 4kg with half the momentum: Ek=1^2/2*4=1/8...
  25. I

    Find the distance x so that the two frictional forces are equal

    Letting the normal force on the pad on the left be 1 and the one on the right be 2, Normal force R1 + R2 = W Since the sled is not rotating, net moment =0, Taking moment about the right pad, W(ℓ/2 + x) - Hh - R1ℓ =0 R1 = W/2 + Wx/ℓ - Hh/ℓ Since the rate of the pads being worn is...
  26. J

    Forces on a crate with friction: find the normal force

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  27. A

    Sign convention of internal forces in vertical bars for bending moment

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  28. A

    Engineering Calculation of the reaction forces on a welded joint

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  29. G

    To prove that three forces are in equilibrium

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  30. warhammer

    Solving Centrifugal Forces in a Rotating Coordinate System

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  31. momoneedsphysicshelp

    Nonconservative Forces Problem with a Model Airplane

    I am sure that the answer will be negative, but I'm not 100% sure on how to solve the problem. My initial answer was -350 J. Please help. Thanks!
  32. E

    External forces on Stokes flow

    in the limit as Re→0 , we can neglect the material derivate of v ( Dv/Dt =0 ) but why in books they always make the gravity effects equal to 0? i can't understand and no one really explains this stuff
  33. G

    To find the resultant of forces on a lamina

    Could I please ask for help with the following question: A lamina is in the shape of an equilateral triangle ABC, and D, E, F are the midpoints of BC, CA, AB respectively. Forces of magnitude 4N, 8N, 4N, 3N, 3N act along AB, BC, CA, BE, CF respectively, the direction of each force being...
  34. L

    Engineering Find the reaction forces of shaft AB

    Given: r1 = 0.75 r2 = 1.5 Ok, i have done statics and dynamics, but this book does things differently than the way i accomplished it in the previous classes. This is for mechanical engineering design class. Here is my question. They take sum of the moments along X, which goes through the center...
  35. A

    What is the relationship between surface tension and forces?

    Hello! To this I did what was recommended and this is what it looks like $$ F = mg $$ $$ F = \rho * V * g $$ $$ F = \ rho * \pi^2 * h * g $$ Than for the surface tension I did the same thing to get an expression for F. $$ y = \frac {F} {2 \pi r}$$ Than tried to get F out and than...
  36. D

    I How viscous forces affect force transmission in hydraulic systems.

    Hi everyone, I have a question that I am struggling and need your help. So I am working on a project which is essentially two syringes, A & B, with different cross-sectional areas, A1 & A2, connected via a tube filled with water. If we assume loss-less system, Pascal's law, the input force...
  37. J

    Equilibrium Forces: Force to Move a Mass

    So I already know the normal force is 268.08 from a previous part of the question. I thought that the friction force must be less or equal to uFN for an object to stay in static equilibrium. So Tcos(angle)=uFN T=uFN/cos(angle)=116.49 But the answer is suppose to be 133.37.
  38. yucheng

    Component forces of a pendulum

    I refer to the website below (for more information): http://www1.lasalle.edu/~blum/p106wks/pl106_Pendulum.htm#:~:text=The forces acting on the,the tension of the string.&text=The net radial force leads,is v2/r.) P.S. I'll insert my specific questions in the following paragraphs in this format...
  39. J

    Fundamental Forces: Spring Question

    ma=-k2l+k1l (ma-k1l)/l=-k (-65.12-35.7)/0.51=-k k=197.69, but answer should be 57.7
  40. J

    Fundamental Forces: finding velocity using different fields and forces

    So I know the acceleration is 0, so the net force is 0. QE=1.6E-3*9.9E3 k hat = 15.84 k hat (thats one force) qv x B = q(v i hat + v j hat) x (0.51 i hat + 0.10 j hat) =q(0.10 v k hat- 0.51 v k hat) =q(-0.41 v k hat) =-0.000656 v k hat Now solving for velocity, 0.000656v=15.84...
  41. J

    Fundamental Forces: Force of one charged particle on another

    So first I did the vector stuff. r2-r1= 1.3 i hat-47.5 j hat-14.5 k hat magnitude = 49.68 magnitude squared = 2468.19 Now plugging it all in... F=9E9*6.3E-3*2.8E-3/2468.19=64.322 y vector, -47.5/49.68=-0.956119 j hat Multiply this by force and I get -61.499 but answer should be -36.14
  42. lola1227

    Forces Experienced On Moon and Earth - What is the mass?

    So, I decided to do Fg=ma I tried 25(9.8)=1.62m m= mass However, when i did it i got a mass of 151 but when i put it into its separate equations, the fg is not 25x larger so fg=ma fg=151(9.8) = 1479.8and then fg=ma fg=151(1.62)= 244.62 but 1479.8/244.62 is not 25 it ends up being 6.05...
  43. J

    Fundamental Forces Problem: Acceleration from Planet

    I know its something to do with my unit conversions because my answer is the right numbers but too small by a factor of 10000. I convert the radius to meters by multiplying it by 1000. I convert the density to kg/m^3 by dividing it by 10. I find the volume using the equation (4/3)*pi*radius^3...
  44. J

    Fundamental Forces Problem: Net Force from Gravity

    So what I did was find each of the forces the masses had on m1 using the above equation. From m2 I found 19.975 in the negative i hat and for m4 i found 29.96 in the positive k hat direction using the above equation. For m3 I used pythagorean theorem to calculate r, which was 3.25 (so r^2 was...
  45. J

    Fundamental Forces: Placing charges along a line so that the net force is zero at a point

    So 0=q1q3/r+q2q3/(13.6-r) 0=-8.5/r-3.63/13.6+3.63/r 0.2669=3.63/r-8.5/r r=-18.2465, but the answer is supposed to be 8.24
  46. F

    Internal forces converting kinetic into potential energy (vice versa)

    Hello, Trivial question: a system is isolated and all its internal forces are conservative. Because of Newton's 3rd law, all internal forces are pairwise and the net internal force is always zero (regardless of the forces being conservative or not) hence the system's total momentum is conserved...
  47. E

    I What is the Lagrangian with constraint forces?

    ii
  48. UserUnique

    Understanding Changing Forces in Equilibrium: A Scientific Approach

    Don't know how to approach this problem. I know how to solve 2 opposite constant forces, but in this problem both forces (water and mercury) change with time, until reaching equilibrium.
  49. F

    Conservative forces, Nonconservative forces and Potential Energy

    Hello, I would like to review and validate some concepts that I have been recently thinking about. Hope this is correct and useful to others that need to refresh these concepts. Forces can be classified as either conservative or nonconservative. Dissipative forces are always nonconservative...
  50. ahmetkalca

    Find the forces in the AB, BE, ED and BC arms

    The system shown is in equilibrium, Find the forces in the AB, BE,ED and BC branches.
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