What is Newtons second law: Definition and 54 Discussions

In classical mechanics, Newton's laws of motion are three laws that describe the relationship between the motion of an object and the forces acting on it. The first law states that an object either remains at rest or continues to move at a constant velocity, unless it is acted upon by an external force. The second law states that the rate of change of momentum of an object is directly proportional to the force applied, or, for an object with constant mass, that the net force on an object is equal to the mass of that object multiplied by the acceleration. The third law states that when one object exerts a force on a second object, that second object exerts a force that is equal in magnitude and opposite in direction on the first object.
The three laws of motion were first compiled by Isaac Newton in his Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), first published in 1687. Newton used them to explain and investigate the motion of many physical objects and systems, which laid the foundation for Newtonian mechanics.

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  1. OlegKmechak

    Is there some geometrical interpretation of force from Newton's Laws?

    dP = F dt dE = F dr or if we introduce ds = (dt, dr) (dP, dE) = F ds And both dP and dE are constant in closed system. Some questions: - How does its implies on definition of Force? - Is there some clever geometrical interpretation of Force? - Why P and E seems almost interchengable?
  2. Asterast

    Tension in the string while it descends

    so I took string below point A and Block as a system. Taking mass of string below point A as m and mass of block M. Taking downward direction as X axis. I get Mg+mg-T, Taking T as tension by upward part of string. Now the question says about block descending with acceleration a. so again forces...
  3. J

    How do I calculate the mass of a moving object?

    Homework Statement Someone mistakenly threw away a lovely couch, and you decide to take it back to your apartment. You push it with a force of 350 Newtons and at 30 degrees below the horizontal at 2 m/s. The coefficents of friction are μs = 0.4 and μf = 0.3. What is the couch's mass? Homework...
  4. gelfand

    Conservation of momentum, collisions - what about friction?

    I would like to check my understanding for this problem : A puck with mass ##3m## is stationary on a horizontal friction-less surface. It is being impacted in an elastic head-on collision by another puck with the mass ##2m## traveling with speed ##u## to the right. Find the speed and direction...
  5. Marleycake

    Net Force and Direction of motion

    Homework Statement Is the direction of net force always in the direction of motion? The Attempt at a Solution I would say no because the net force could be equal/balanced for example if two kids were pulling on a stick 2 N left <---- . ----->2 N right the Total Net Force would be 4 N with...
  6. Frankenstein19

    Help with free fall and Newtons second law problem

    Homework Statement Using Newtons second law, if an object with mass M is free falling (the only F acting upon it is its own weight), calculate the object's acceleration. What would happen to its acceleration should its mass duplicate? Homework Equations F=ma The Attempt at a Solution So...
  7. Prof. 27

    Tension and Newtons Second Law

    Homework Statement A student tries to raise a chain consisting of three identical links. Each link has a mass of 200 g . The three-piece chain is connected to a string and then suspended vertically, with the student holding the upper end of the string and pulling upward. Because of the...
  8. F

    Newton's second law and how to calculate the force on the mo

    I, earlier were studying Newton's second law F=ma, or rather the free fall of objects, F=mg. A thought occurred to me, how do I apply this formula to the moon with the Gravity of 1.622m/^2 and came up with F=m(g/6), however, g/6 = 1.63m/s^2 Normally I'd just use F=ma, but assuming people one...
  9. D

    Is mgsinθ=static frictional force on an inclined plane?

    According to Newton's 3rd law, for every force there's an equal opposing force. Since a block is sitting on an inclined plane, wouldn't that mean the static friction is acting like the opposing force for mgsinθ thus, mgsinθ=static frictional force? Please respond
  10. copypacer

    Bow and arrows, Newtons second law of physics

    Homework Statement If I have shot an arrow, would that arrow speed slow down due to air resistance? If so, would that mean that the the acceleration would be de-accelerating? Homework Equations f = ma The Attempt at a Solution This isn't a a homework problem, this is just something I was...
  11. H

    What constant force does the floor exert

    Homework Statement A 74.4 kg person falls straight down from a 1.96 m height (measured from his feet) and lands with weight distributed equally on both feet. To soften the blow, he bends his knees so that it takes 0.906 s for him to stop once his feet touch the ground. What constant force does...
  12. S

    Circular Motion and Gravitation of tether ball

    Homework Statement There is a tether ball swinging around in a uniform circle on a rope that is 1.90m long. Marcus hit the ball so hard that the string holding the ball made a 20.0 degree angle to the horizontal. What is the tension in the rope if the ball has a mass of 1.40 kg? Assume that the...
  13. K

    What is KE of the system using F = ma ?

    Homework Statement Three particles of mass all = 3 kg are located at the vertices of an equilateral triangle and are spinning about their center of mass in an empty space. The sides are length d = 2 m which doesn't change with time. Homework Equations What is the PE of the system? What is the...
  14. T

    Calculating Tension and Friction in Newton's Second Law Problems

    Homework Statement Homework EquationsThe Attempt at a Solution I'm not sure if their are frictional forces on the cart and the mass m. Also do I have to somehow get the length of the bar involved ?, not sure how to do that. Also is their a tension acting on the bar ?
  15. T

    Buoyant Force & Gravity Force find Fnet (Newtons Second Law)

    Homework Statement A 4 kg book sinks a distance of 5m in the ocean starting from rest. The volume of the book is 0.00266666666666667 m^3. We assume the velocity of the Earth is zero during the whole process, and gravity and the bouyance force are the only interactions of the book. (Note...
  16. V

    3 Cars Meets Newtons Second Law

    This is not a homework problem - I am trying to understand the physics of something that happened to me. Scenario: two cars are stopped at a red light. Car #1 in front, and behind it is car #2. Car #3 comes up from behind, does not stop, and hits car 2, and car 2 in turn hits car 1. I am...
  17. M

    Where did Newtons Second law come from?

    I want to preface this question with the fact that I am a scum noob. How did Newton come up with the second law of motion. As I understand it, it is only derived through experiential observations. I have tried many different Google searches but I can't find anything relevant.
  18. N

    Newtons second law and kinematics

    1)A rock is dropped off a cliff and falls the first half of the distance into the ground in t1 seconds. If it falls the second half of the distance in t2 seconds, what is the value of t2/t1? Relevant equations: I think the kinematics equations of d=vt+(1/2)at^2 I have no idea how to solve...
  19. N

    Ap physics questions on basic kinetics and Newtons second law

    1)A rock is dropped off a cliff and falls the first half of the distance into the ground in t1 seconds. If it falls the second half of the distance in t2 seconds, what is the value of t2/t1? Relevant equations: I think the kinematics equations of d=vt+(1/2)at^2 I have no idea how to solve...
  20. N

    Integration Newtons Second Law

    Homework Statement Hi In a book they state \frac{dv}{dt} = a \quad \Rightarrow \quad v(z) = \sqrt{2a(z-z_{max})} I am trying to reproduce this. Here is what I have so far: dv/dt = (dv/dz)(dz/dt) = v(dv/dz) = a Since a is constant (I assume?), I get \int vdv = \int adz \quad...
  21. G

    Forces using Newtons Second law

    Homework Statement A 1300 kg car in neutral at the top of a 17° inclined 10 m long driveway slips its parking brake and rolls downward. At what speed will it hit the garage door at the bottom of the incline? Neglect all retarding forces. Homework Equations (sin17) (cos17)...
  22. G

    Forces using Newtons Second law

    Homework Statement A bullet fired into wet clay will decelerate fairly uniformly. If a 10 g bullet hits a block of clay at 235 m/s and comes to rest in 17 cm, what average force does it exert on the block? [Hint: From the fact that the bullet goes from vi to 0 in a distance s, you can find aav...
  23. C

    Problem using Newtons second law

    Once her chute opens, a sky-diver of mass m is acted upon by a downward force Fg due to gravity, and an upward force Fr due to air resistance. If Fg = mg, where g is gravitational acceleration, and Fr is proportional to velocity v, use Newton’s Second Law of Motion to write acceleration a as a...
  24. V

    Conservation of momnetum or Newtons second law?

    conservation of momnetum or Newtons second law? Homework Statement An acrobat of mass 'm' clings to a rope ladder hanging below a balloon of mass 'M'. the balloon stationary with respect to ground (a) If the acrobat begins to climb the ladder at a speed 'v' (with respect to the ladder), in...
  25. N

    Newtons second law about momemtum

    Homework Statement a mass of 10kg, initially at rest, is acted on by a force of 10N for 10 s. What is the final velocity of the mass? Homework Equations i think this equation should help: F= change in momentum/ time The Attempt at a Solution hey everyone i am out of school so...
  26. N

    The title of this page could be: Newton's Second Law Homework: Constant Term

    Homework Statement Hi Say I am given Newtons second law in this form: \frac{{d^2 x}}{{dt^2 }} + \gamma \frac{{dx}}{{dt}} + \omega _0^2 x + const = 0 I know the physical interpretation of all terms except the last one, i.e. the constant. Does this go into the restoring-force term...
  27. P

    Newtons second law for coupled oscillators

    Hello there! Could someone please help me with setting the starting equations for coupled oscillators. I'm having serious troubles with setting the +- signes right (yes, more than with the differental equations :) ). OFF TOPIC: any reading materials about problems with signs in physics will...
  28. R

    Newtons Second Law For A System Of Particles

    Homework Statement In figure (a), a 5.4 kg dog stands on a 16 kg flatboat at distance D = 6.1 m from the shore. It walks 2.1 m along the boat toward shore and then stops. Assuming no friction between the boat and the water, find how far the dog is then from the shore. Homework...
  29. M

    Stuck on Newtons Second Law Prblem

    Homework Statement The only force acting on a 4.3 kg body as it moves along the positive x-axis has an x component Fx = -8x N, where x is in meters. The velocity of the body at x = 1.6 m is 11 m/s. (a) What is the velocity of the body at x = 4.5 m? (b) At what positive value of x will the body...
  30. P

    Newtons second law perspective problems

    I'm having some problems in observing the total force which. The original situation is numbered "1." There is a resultant force F_r = m_2 \cdot g - k \cdot m_1 \cdot g and because of that force m1 has the acceleration a. What I can't seem to figure out is is that resultant force...
  31. T

    Apparent Weight and Newtons Second law Problems

    Homework Statement 1. The first problem states that an elevator moves downwards with an acceleration of 3.36 m/s^2 with someone inside that has the mass of 64.2 kg. Now what is the apparent weight? 2. Blocks A and B are right next to each other. If 5.1 N were applied on block A, calculate...
  32. E

    Tension/pulley problem, Newtons second law

    Homework Statement Two objects A and B, with masses m1=1.00kg and m2=2.00kg, are connected with an ideal string. Object A is moving on an ideal incline with 0 friction. Object B is moving vertically. A force F is working on object B. Its magnitude is 6.00N. Object b is accelerating downward...
  33. B

    Newtons Second Law: Finding net forces

    Homework Statement A spaceship lifts off vertically from the Moon, where g = 1.6 m/s2. If the ship has an upward acceleration of 1.0 m/s2 as it lifts off, what is the magnitude of the force exerted by the ship on its pilot, who weighs 735 N on Earth? From Halliday, Fundamentals of Physics...
  34. P

    Problem with Newtons second law

    hello! here's my problem: Newtons second law implies: F=m*dv/dt+v*dm/dt first part of the equation says if I act on the object then it's reaction will be acceleration, but the second part says if act on the object it will cause changes in object's mass. In case where I'm dealing with non...
  35. T

    Maximizing Acceleration and Braking Distance for a Cyclist on a Horizontal Road

    Homework Statement A cyclist and her bicycle have mass 75kg. she is riding on a horizontal road, and positions herself so that 60% of the normal contact force is on the back wheel and 40% on the front wheel. The coefficient of friction between the tires and the road is 0.8. What is the...
  36. A

    Applying Newtons Second Law to Vertical Motion

    18. An elevator that weighs 3.5 x 103 N is accelerated upward at 1.0 m/s2. What force does the cable exert to give it this acceleration? A. 357 N B. 0 N C. 3500 N D. 3857 N (For this quesion I was really confused and I guessed that the force of tension in the cable was what the cable...
  37. S

    Basic Newtons second law plus friction

    Homework Statement A person pushes horizontally with a force of 220 N on a 50 kg crate to move it across a level floor. The coefficient of kinetic friction is 0.25. (a) What is the magnitude of the frictional force? (b) What is the magnitude of the crate's acceleration? Homework...
  38. S

    Newtons Second Law Formula Question

    Homework Statement I've been given a problem that an object falls from a distance of 800 feet with an initial velocity of 4 f/s. Gravity acts on the object, but air resistance can be disregarded. Find the location at time t and find when the object hits the ground. The Attempt at a...
  39. A

    Free fall and Newtons second law

    Homework Statement A person jumps from the roof of a house 4.4 m high. When he strikes the ground below, he bends his knees so that his torso decelerates over an approximate distance of 0.70 m. The mass of his torso (excluding legs) is 40 kg. (a) Find his velocity just before his feet...
  40. 1

    Help with Newtons Second Law Question Please.

    Homework Statement Calculate the force needed to accelerate a 2.0kg ball at 3.0ms^2 (A) In space, a long way from Earth. (B) On a frictionless horizontal surface, near the surface of the earth. (C) vertically upward, near the surface of the earth.Homework Equations F = m*a The Attempt at a...
  41. Y

    Quesiton on Newtons Second Law, Need Help.

    Two blocks of identical material(Block1 20kg, Block2 10kg) are connected by a light rope on a level surface. An applied force of 55Nright causes the blocks to accelerate. While in motion, the magnitude of the force of friction on the block system is 44.1N. 2. Homework Equations...
  42. A

    Project for Newtons Second Law of Rotational Motion

    Any help would be appreciated. I'm supposed to make a 20 slide project in power point to depict how angular acceleration, net torque, and moment of inertia are related to one another, as sated in Newton's Second Law of Rotational Motion. I'm supposed to describe the basic concept of the Law and...
  43. G

    How Can I Apply Newton's Second Law with Friction in Real-Life Problems?

    ok, i need some serious help with Newtons second law. like i kind of understand it, but adding things like friction are giving me real problems. does anyone have any good resources or tips on how to understand/comprehend this? and i have a prolem: a man pushes a 15 kg lawnmower at constant...
  44. J

    Rotation with Newtons second law and work energy

    Heres the problem http://img141.imageshack.us/img141/2820/49686394mt3.jpg Now I have to work it out using Newtons second law and Work energy... For Newtons second Law (F = ma)...would I be using I = mk^2 M = I\alpha than setting up F = ma...? and for work energy I am...
  45. T

    Slope Represents Newton's Second Law

    [SOLVED] Newtons Second Law Homework Statement On a force/mass vs acceleration graph where force/mass is horizontal, what does the slope represent? Homework Equations The Attempt at a Solution My calclations: ex. (2m/s^2 - 1m/s^2)/(3 N/kg - 1N/kg) =.5 (m/s^2)/(N/kg)...
  46. K

    What is the maximum acceleration a runner can achieve with 90% friction?

    Hey all, I am new to Physics. Recently changed majors from technical writing to physics for the amount of interest I have in the subject. I have been doing ok but I missed a couple of questions on my last homework and I feel that I should have had somebody check my general solved statements...
  47. S

    How Much Force is Needed to Accelerate a 1000 kg Car at 2 m/s²?

    Newtons second law problem, show all work including units Question: How much horizontal net force is required to accelerate a 1000 kg car at 2 m/s^2?I am not sure which formula to use in this equation
  48. S

    Newtons 2nd Law: F=ma Along x,y or z Direction

    Homework Statement F=ma can be written as F=ma(along x, y or z-direction, ) when applying this equation along say horizontal x direction, the direction of acceleration needs to be taken as it is a vector. i mean say 2 forces of 5 N and 3 N are applied on a 2 kg body that moves towards...
  49. A

    Fbd problems using Newtons second law

    i need help with this problem please help (If you use a horizontal force of 30.0 N to slide a 12.0kg wooden crate across a floor at a constant velocity, what is the coefficient of kinetic friction between the crate and the floor?) PLZ HELP AHHHHH ITS DUE TMRW SO PLZ HELP
  50. L

    (Newtons second law) One of the two problems I really need to solve this weekend

    Could anybody of you verify my answers here please... it's really important for me to know if I'm doing it right! A mass m2= 10 kg slides on a frictionless table. The coefficients of static and kinetic friction between m2 and m1 = 5 kg are us= 0.6 and uk= 0.4...