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. V

    Derivation of Aerodynamic Forces

    Good day all: I'm having trouble deriving the forces for Lift and Drag in the attached diagram. The text I have (Fundamentals of Aerodynamics - John Anderson) states the solution to be: L = N cosα - A sinα D = N sinα + A cosα Can anyone guide me through this? I think the cofunction identity...
  2. B

    How Do You Calculate the Other Student's Force on a Trunk in Physics?

    Homework Statement Two students push horizontally on a large, 65kg trunk. The trunk moves east with an acceleration of 2.0m/s^2. One student pushes with a force of 2.2x10^2 N[E 42 degrees S]. The force of friction acting on the trunk is 1.9x10^2N[W]. Determine the force that the other student...
  3. c1tonsoup

    Statics: parallel forces problem

    Homework Statement Determine the x- and y-coordinates of a point through which the resultant of the parallel forces passes. The Attempt at a Solution The first thing I did was to find the resultant forces, which is R = 0i + 0j -125 k Then I found the moment of each axis so M = (-65(12)...
  4. B

    Determining Direction of Tension Force: Find Answers Here

    Homework Statement How do you determine the direction of tension in a force/ the direction of tension acting on an object. I'm confused. Homework Equations - The Attempt at a Solution I have no clue. Help!
  5. Biker

    Internal and external forces in momentum

    Homework Statement A question came to my miind: Wouldn't everything be conserved? I know that the law of momentum conservation only applies when the system doesn't have any external forces or the net of them is equal to 0. Lets just say that someone hits the ball with a bat, He applies a force...
  6. heartshapedbox

    Newton's first law, forces, charges

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  7. King_Silver

    Calculating Vertical +Horizontal Forces of Beam in Equilib.

    Homework Statement Below are attached 2 beams, A and B. I have to calculate the vertical and horizontal reactions at both supports in both questions. I have done a lot of calculations and believe I have a good understanding of what is needed to be done however my forces are not balancing for...
  8. H

    Prove forces of semiholonomic constraints do no virtual work

    I do not see how (2.34) shows that forces of semi-holonomic constraints do no work in the displacements ##\delta q_k## between the varied path and the actual path. Starting from (2.31), I seem to be able to prove that such forces do do work, in contrary to what is claimed in the paragraph...
  9. A

    Component forces on angle bracket

    Homework Statement See photo attachment Homework EquationsThe Attempt at a Solution Ive begun by defining an x and y axis, followed by find the sum of x-components of the forces, and y-components. Followed by the magnitude of the resultant force. The only method i could think of was to find...
  10. N

    Need help with the 4 fundamental forces of Nature

    Hey everyone, I am currently in the middle of research for a science fiction /fantasy novel where the magic system is based on the ability of a group of people to manipulate the four fundamental forces of physics. Of these four, coming up with ways that individuals could manipulate gravity and...
  11. D

    Forces of a basin surrounding a drain

    Homework Statement A basin surrounding a drain has the shape of a circular cone opening upward, having everywhere an angle of 34.5° with the horizontal. A 28.5-g ice cube is set sliding around the cone without friction in a horizontal circle of radius R. (a) Find the speed the ice cube must...
  12. B

    Inertia: Internal Forces & Object Motion

    Homework Statement My textbook says that internal forces have no effect on an object's motion and that external forces are required to change the motion of an object. But, we looked at an expirement where a raw egg was spun and then stopped. After being stopped, it went back to spinning...
  13. B

    Cylindrical barrel Hydrostatic Pressure

    Homework Statement A circular cylindrical barrel is half full with oil. If the diameter of the base is 8.0 m, find the net force against each end if ρo = 800 kg/m3. The cylinder is on its side. Homework Equations F=P*A P=ρgdy The Attempt at a Solution P = ρo*g*h, where h is the radius which...
  14. W

    Formula of Forces: 2.1 & 0.35 Meaning

    Homework Statement what is the 2.1 and 0.35 refers to in the equation of (9810)(2.1)(4.2)- 9810(0.35)(0.7) -Fx = 1000(5.88)(8.4-1.401) ?? is it the width ? but , the width is not given ? Homework EquationsThe Attempt at a Solution
  15. mgkii

    Exploring Feynman's Tidal Forces: A Deeper Look

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  16. Z

    Ratio of Forces by from Tennis Serve?

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  17. W

    Understanding Forces on Submerged Surfaces

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  18. M

    Exploring the Forces and Impulse Impacting a Bouncing Basketball

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  19. avorobey

    Work and forces in systems of many particles

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  20. kanibal

    How to calculate (mechanical) clutch forces

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  21. GadgetStrutter

    Joining the Canadian Air Forces + Get Paid for Physics

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  22. B

    Can't figure out solution -- Space probe with engine thrust vectors

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  23. P

    What is the driving resistance force?

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  24. Phy_TR

    Help with Electric Forces Problem and Equilateral Triangles

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  25. M

    Forces exerted somewhere other than CM

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  26. klotza

    Insights Secondary Forces Explored - Comments

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  27. K

    Forces on an inclined plane with a pulley

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  28. komarxian

    Rollercoasters and Loops and Normal Forces

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  29. UMath1

    Why Don't Intermolecular Forces Play a Significant Role in CO2 Molecules?

    I understand that due to the geometry of the CO2 molecule it ends up have no net dipole moment. But why doesn't the central carbon atom experience intermolecular forces from the oxygen atoms of other CO2 molecules. What I mean is why can't CO2 form an arrangement where the dipole forces still...
  30. B

    Newton's Third Law and a canoe

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  31. B

    Forces on a Skydiver during the initial frefall phase of the jump

    Homework Statement A skydiver is jumping out of an airplane. During the first few seconds of one jump, the parachute is unopened, and the magnitude of the air resistance acting on the skydiver is 251N. The acceleration of the skydiver during this time is 5.96 m/s^2 [down]. Calculate the mass of...
  32. B

    How Does Friction Impact Bobsled Acceleration?

    Homework Statement In the men's four-man bobsled event in the winter olympics, the maximum mas of a bobsled with pilot, two riders, and a brakeman is 630 kg. During a practice run, the rear rider and the brakeman exert average forces of 1220N and 1200N [forward] respectively to accelerate a...
  33. B

    What force causes a body to move into the windshield when a car suddenly stops?

    Homework Statement This is not a specific problem, I was just wondering, what unbalanced force acts on your body when you are in a car traveling at a constant velocity and the car comes to a sudden stop? This has to do with Newton's First Law, but I'm unsure of what force applied to your body...
  34. P

    Effect of internal forces on the weight of a body.

    + A man is holding a closed cage on the palm of his hand with a bird in it. When the bird flies with an upward acceleration inside the cage, it feels heavier. But the force due to the bird in the cage is actually an internal force on the cage, and internal forces don't cause acceleration of...
  35. D

    Balancing Electric and Gravitational Forces Between Two Objects

    Homework Statement Two small objects of equal mass 3.0g are placed a certain distance apart. How many electrons must be transferred from one to the other so that the electric force between them is equal to the gravitational force between them? Homework Equations Coulomb's Law: F = K...
  36. N

    Centripetal forces in our solar system

    i calculated the centripetal forces in our solar system but i can't seem to find a connection using the centripetal force formula: Fmpz=(m⋅v2)/r i found out that the mean centripetal force for the planets around the sun is about 10^39, the mean centripetal of the moons around Jupiter is about...
  37. H

    Will this rope break due to the tidal forces or not?

    While I was thinking about how tidal forces can make objects float at the surface of a planet orbiting a massive object like a black hole, the fact that any material on the Earth isn't held together by gravity only, but also by chemical bonds which give it its tensile strength came into my mind...
  38. B

    Calculating acceleration of plane when given mass, friction force and Vi

    Homework Statement A 2000 kg plane is landing at an airfield with an initial speed of 50 m/s. The force of friction is 1/4 the weight of the plane. What is the acceleration of the plane? Homework Equations Fnet = ma Fnet = something - ff The Attempt at a Solution 2000a = thing I don't know...
  39. Rod Alexei

    Basic Forces Question from 9th grader - Hard to put in words

    Homework Statement I have here a problem asking me to find the tension force on the lower end of a rod with mass of 0.6 kg. The rod connects two blocks, the first / upper one has a mass of 5.0 kg while other/lower one has a mass of 4.0 kg. There is an upward force of 150 N applied on the whole...
  40. Rumplestiltskin

    Felix Baumgartner's parachute jump from space -- forces and velocities....

    Homework Statement a)ii) Calculate the upward force F acting on Baumgartner at this point. (3 marks) total mass of Baumgartner = 95 kg g = 9.8 ms-2 b) Describe the shape of the graph between 30s and 70s. Explain the velocity changes in terms of changes in the air through which Baumgartner was...
  41. AntoineCompagnie

    Potential energy variation = work of -(conservative forces)

    Homework Statement Why is potential energy variation between two points equals to the work of the opposite of conservative forces between these two points? Homework Equations If we call these forces $$\vec F_ext^C$$ \begin{equation} \Delta E_p=E_p(B)-E_p(A)=-\sum W_{A\rightarrow B}(\vec...
  42. H

    Understanding Force Formula: ρ AV1 (V1 - V2 cos θ) vs ρ A(V1 - V2 cos θ)

    why the Fx is given by the formula = ρ AV1 ( V1 - V2 cos θ ) , why not = ρ A( V1 - V2 cos θ ) ?
  43. S

    Intermolecular forces and boiling point

    I've come to understand that intermolecular forces cause the boiling point of hydrochloric acid solutions below 20% to be higher than the boiling point of water. I also understand that dissolving hcl in water is an exothermic reaction. But, what about those intermolecular forces. I assume they...
  44. J

    Forces on an Object Sliding at 8.0 m/s

    Homework Statement An object slides across a table at a constant 8.0 m/s to the right. The net force is... A) zero B) equal to the weight C) equal to the mass times the velocity D equal to the friction force Homework Equations N/A 3. The Attempt at a Solution Bu narrowing it down i don't...
  45. Satvik Pandey

    Masses colliding because of central forces between them

    Homework Statement A particle is been acted by a central force exerted by a sphere of mass 'M' at a distance 'xo' initially from the particle (of same mass). At t=0 the particle has velocity Vt perpendicular to the line joining the particle and the center of the sphere. Find the time at which...
  46. H

    Electric Forces in 1D Motion

    Homework Statement In outer space, a ball with mass 0.25kg and charge +4/K C is shot from 5m towards a +0.5C charged ball with an initial velocity of 20 m/s What main Physics principle should be used to solve this problem? What is the closest the small ball will get to the large one? What is...
  47. C

    Calculating Forces and Angles in a Model Plane System

    Homework Statement A motorised model plane is attached to a light string anchored to a ceiling. The plane follows a circular path of radius 0∙35 m as shown in Figure 2. The plane has a mass of 0∙20 kg and moves with a constant angular velocity of 6∙0 rad s−1 . (a) Calculate the central force...
  48. seb7

    Electrostatic Forces: Attraction vs Repulsion

    Hi, two questions: Does the same energy put into an attraction force give the same force as a repulsion force? I am wondering if one is measuring slightly weaker than the other. ie. If I measure the positive/negative attraction force, is the positive/positive repulsion force as strong when...
  49. Y

    Reaction forces in a two segment beam

    Homework Statement Homework Equations ∑Fx=0 ∑Fy=0 ∑M=0 The Attempt at a Solution [/B] I am just concerned with part a. I got the correct answers doing this: First, FBD of segment AB: +cw ∑M_A=0: -136 - 6*By = 0 By = -22.7N two ways to get Ay: one: +cw ∑M_B=0: -136 + 6*Ay = 0 Ay =...
  50. L

    Forces in symmetrical construction

    Homework Statement We have a slab with uniform distrubuted load on it W. All dimensions. [/B] I'm looking for the force on the bolts and force on the hook contact surface. The Attempt at a Solution My way to do it is to reduce the problem for 2D. But the problem is that I'm not sure how to...
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