Newton's laws Definition and 478 Threads

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. M

    Determine the velocity of a package dropped from a satellite

    Momentum before ejection P_b: P_b= (M+m)*v_M=8*500=4000, since the package is still on the satellite and isn't moving. Momentum after ejection P_a: according to the law of conservation of momentum P_b=P_a, and this gives me: 4000=450*8 + v_m*50 => (4000 - 3600)/50 = v_m = 8 km/s But according...
  2. tellmesomething

    Understanding Stress and Strain: The Relationship Between Two Variables

    I was going through the stress-strain curve and I realized that strain is taken as the independent variable and stress as the dependent variable. In reality is this true or is it the other way around?I saw a lot of answers on Quora that say that strain is the cause and stress is the effect. But...
  3. paulimerci

    Newton's Laws of motion -- Bicyclist pedaling up a slope

    F parallel - F applied - rolling resistance = ma I don't know how to calculate for rolling resistance. If the bicycle is not slipping rather it is rolling, should I ignore rolling resistance? And if I ignore that I would get, F parallel - F applied = ma F applied = F parallel -ma...
  4. paulimerci

    What is the difference between friction and rolling resistance?

    How to find frictional force when coefficient of friction is not given?
  5. dextercioby

    I Extending Newton's laws -- Is the concept of force still defined?

    It is argued that the correct interpretation of Newton's 2nd Law for one body of mass ##m## reads "The dynamics (i.e. vector sum of all external forces acting on the body = "all its interactions") dictates the kinetics (i.e. time derivative of the momentum vector = "motion")", under the...
  6. sachin

    Choosing what consists of a "system" in Newton's laws of motion

    The question is solved in a single step by taking the blocks as a system and using conservation of linear momentum in the horizontal direction as there is no net force acting in the horizontal direction. Conserving the momentum we get, m x v + M x 0 = (m+M)v', so,,v' = mv/(m +M).where v' is the...
  7. S

    How can l prove that Newton's laws are time invariant?

    how can l prove Newton's law is time invariant? if x (t) is a solution of dd/ddx x(t) = f(x(t)) then if l put y(-t) dd/ddt y(t)=dd/ddt x(-t). Now how dd/ddt x(-t) is equal to f(x(-t))?dd/ddt is second derivative with respect to time
  8. S

    Apparent weight problem (kinematics + conservation of Energy + Newton's laws)

    Hello there, I have tried the problem but don't get a different of 6g's as I am supposed to. I am not sure whether I interpreted the problem in the correct way, but I would love some feedback/hints on what went wrong in my solution, thanks in advance. Solution: SITUATION DRAWINGS + FBDS so...
  9. royaljelly

    I Are Newton's Laws just definitions?

    I have read a bunch of articles online regarding my question, and none have helped. Newton's Laws: 1. In an inertial reference frame, an object's momentum doesn't change unless acted upon by a force. 2. In an inertial reference frame, the force on an object equals the time derivative of its...
  10. Angetaire

    Solving Physics Problem with Angles and Trigonometry

    The correct solution uses angles and trigonometry. My solution is as following: - Suppose the forces exerted by friends 1 and 2 are F1 and F2 respectively. - There are no net force in the x-direction, so F(total x) = 0. - F(total y) = F1 + F2 - mg = 0 (initially). Rearranging gives g =...
  11. kara123

    Newton's laws of motion -- Force of gravity on a skydiver

    I think you would do force of gravity= mass x acceleration acceleration of gravity= 9.8 m/s mass 75 kg 75kg x 9.8 m/s =735 N i don't know if that's right but i have no idea how to calculate it after he lands, any help would be greatly appreciated!
  12. nirlalush

    Newton's laws — Two stacked blocks sliding on a frictionless floor

    hello , I am adding pdf with the questions and what i tried to do to solve them. in the first question my teacher just taught us that if there is a frictionless floor and i push the upper block (m) with force F toward me then if the static friction will be toward me too. so the lower block M is...
  13. Thytanium

    I Are Newton's Laws of physics compatible with thermodynamics?

    Good day friends. I want to know and ask you if Newton's laws are incompatible with thermodynamics.
  14. S

    I Newton's Laws with one body inside another

    Hello All What would be the motion of a weight dropped into a hole drilled all the way through an Earth-sized planet? Would the weight accelerate all the way to the centre and then decelerate until it got to the far side, and repeat this motion forever? OR Would it accelerate initially and...
  15. li dan

    I Would this violate or challenge Newton's laws?

    The phenomenon of diffusion is a transport phenomenon based on the thermal motion of molecules, a process in which molecules are transported from a region of high concentration to a region of low concentration by Brownian motion. Let's assume that there is a car, the road under the wheels is...
  16. petha1

    Some homework questions in astrophysics (Kepler's Laws, Newton's Laws)

    1. Keplers third law (and the asumption that M1+M2 ~ M1) gives that M_Mars = 4*Pi^2*a^3/(G*T^2) With numerical values inserted Mmars = 4*3.14^2*(9400*1000+3396.97*1000)^3/((6.67*10^-11*(7*60*60+39*60)^2) 2. Phobos needs 7h39 minutes to complete a circle, this gives a speed of...
  17. 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?
  18. J

    Applications of Newton's laws - coefficient of friction

    https://www.physicsforums.com/attachments/277763
  19. yucheng

    Why are these pulleys equivalent?

    I have to apologize if the diagram is awful: I drew it for the sake of asking... I am analyzing the rope that is hanging the pulleys. From the diagram, the pulley at the left (let's call it L), has two objects with mass M at both ends. The pulley at the right (let's call it R), has an object...
  20. Lucho G

    Are there situations in which Newton's laws are not fulfilled?

    Please I require solutions to this question about Newton's laws thank you
  21. M

    Empirical and Definitional Content of Newton's Laws

    I'd like to get a better insight into which aspects of Newton's laws are definitional and which are falsifiable. And moreover, of the definitional aspects, why these are good definitions. Netwon's laws can be phrased as follows (from Wikipedia): First law: In an inertial frame of reference, an...
  22. jk22

    Newton's laws of motion in 3+1 dimensions ?

    If it were supposed that time were a 4th non-spatial dimension how would it influence the gravitational movement ? The problem I have when trying to solve this invented problem is that Newtonian physics works in coordinates and that there are a lot of ways to find 4d 3+1 hyperbolic-spherical...
  23. BayMax

    Double pendulum equations of motion using Newton's laws

    I need help to understand this problem taken from Mechanical Vibrations by S. Rao I know that the equations of motion could be obtained in various ways, for example using the Lagrangian, but, at the moment, I am interested in understanding the method he used. In particular, if I'm not...
  24. Adesh

    What's my mistake in this problem in dynamics involving pulleys?

    Find the acceleration of block A and B, given that the mass of pulleys and strings are negligible.. I could see that the block B has gravity acting on it, therefore the gravitational force on the block ##B## is ##F_B = 5 g## and hence the acceleration is ##g##. From the pulley to which...
  25. A

    Calculating the normal force with Newton's Laws

    Block A is accelerating at a= 49.6/0.5 m/s (99.2m/s) Block B force is F= 3kg * 99.2 = 297.6N but I'm not sure where to go from here?
  26. bhobba

    What Do Newton's Laws Say When Carefully Analysed

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  27. mayalevy2

    How do I solve this physics problem of mechanics and Newton's laws?

  28. S

    Using Newton's Laws: Friction, Circular Motion, Drag Forces

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  29. A

    Newton's Laws — Pushing a box horizontally on a surface

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  30. caters

    What is the period of this binary orbit?

    Okay, so let's simplify things and look at the ideal case, where the 2 masses are the same. Well, this gives us a sine wave pattern to the orbital velocity. Consequently, the acceleration would follow a cosine wave since the derivative of velocity is acceleration and the derivative of sine is...
  31. G

    Does the mass of an object affect its inertia?

    I know what the answer is supposed to be, but I don't understand why. Here is my logic as to why I thought a few of these suggestions should be the right answer. "C) Mass is a measure of an object’s ability to resist motion or movement of any kind." Considering F = ma, and that mass is...
  32. A

    Rigid body mechanics, solution seems incorrect?

    I've attached the problem and solution as picture. To my understanding, the gear E and the rod OB are taken together as the rotating rigid body. However, the equations of motion and (##∑F = macm##) are applied to the center of mass of the rod, G, rather than the center of mass of the rigid body...
  33. NotSoRobot

    Newton's Laws Homework question: Double incline mass problem

    Homework Statement I have a double incline mass problem where Φ=43° and θ=20°, mass_A=1.00kg and they are connected by a massless string where the net force of each block is equal to 0. Homework Equations I believe I am to use Newton's 2nd law to find the force of the tension which I have next...
  34. N

    Newton's Second Law: Understanding Forces, Masses, and Acceleration

    Homework Statement Two identical trucks traveling at different constant speeds are about to collide. The trucks are traveling in opposite directions with truck A going at a velocity of 3m/s right and truck B going at 4m/s left. During the collision, will the magnitude of the acceleration of...
  35. J

    Using conservation of energy vs. Newton's laws in a pulley problem

    The problem is attached in the photo. The correct answer, according to the teacher's solution, was obtained using conservation of energy. Initially I tried using Newton's law/kinematics and got the wrong answer. Why didn't this work? Can you ever use Newton's law/kinematics to solve pulley...
  36. bhobba

    What Is The Meaning Of Newton's Laws

    Here are Newtons Laws 1. A particle at rest stays at rest or continues to move in a straight line at constant velocity unless acted on by a force. 2, Force is mass x acceleratoion 3 To every action there is an equal or opposite reaction. What are they saying? Well 1 follows from 2 which...
  37. S

    Newton's laws of motion: A gun firing bullets....

    Homework Statement A gun fires bullets each of mass 1g with velocity of 10m/s by exerting a constant force of 5 g weight. Find the number of bullets fired per second (take g=10 m/s2). Homework Equations F=ma M1U1 + M2U2 = M1V1 + M2V2 (conservation of linear momentum) The Attempt at a...
  38. PrathameshR

    Conceptual questions about Newton's Laws....

    Homework Statement I can't find answers to following questions in the book Concepts of Physics by H. C. Verma.1. The apparent weight of an object increases in an elevator accelerating upward. A peanut seller sells his peanuts using a beam balance in an elevator. Will he gain more if elevator...
  39. CAT 2

    Applications of Newton's laws (friction related)

    Homework Statement A child pushes a block of wood with a mass of 0.72 kg across a smooth table. The block starts from a position of rest and after 2 seconds its has a velocity of 1.6 m/s [forward] The coefficient of friction is 0.64. a) Find the net force acting on the block of wood. b) Find...
  40. thebosonbreaker

    Why were Newton's laws of motion discovered so late?

    Hi, I had a thought recently which gave rise to a rather interesting query. A helicopter works and is able to fly due to Newton's third law of motion. The propellers rotate at a high speed and exert a force on the air beneath them. By N3L, the air therefore exerts an upwards force on the...
  41. thebosonbreaker

    A question about Newton's laws & free body diagrams....

    Here I have drawn the free-body diagram for a rock (but could really be any object) which is being pulled upwards. Fa represents the applied force (let's say...by a rope) Fg represents gravity/weight of the object Ff represents friciton, i.e. the small amount of air resistance But here's my...
  42. E

    Newton's laws -- Blocks and pulleys problem with friction....

    Homework Statement The coefficient of friction between A and the table is μA. The coefficient of friction between A and B is μB. A, B, C and D all move with an acceleration of 2m/s^2 (A and B move to the left). Find the force that the friction between the bodies apply on B. Find the tension of...
  43. E

    Newton's laws: Block/Pulley/Wedge/Friction

    Homework Statement No friction between m2 and M. The static friction between M and the floor is μs and the dynamic is μd. When F=0, what is the minimal static friction if M doesn't move? Homework Equations F=ma Force caused by friction: μN=F The Attempt at a Solution What I thought is that...
  44. F

    Motion predicted by Newton's laws

    Hello The following thought is confusing me a little. Let say we have sphererical planet with a certain mass and radius fixed in space. Now we have a point particle that at time t0 has a velocity vo that is perpendicular to the vector from the center of the plant to the particle and has a...
  45. L

    Is this a mistake on the answer key? (Newton's Laws)

    Homework Statement Homework Equations F = ma [/B]The Attempt at a Solution Why is the angle 60 degrees? Isn't it 30 degrees? [/B]
  46. Q

    News What experiments did Newton conduct to determine his Laws of Motion?

    Hello Everyone ! I am interesting to find descriptions of the series of experiments that Newton made for determining the laws of motion. In English of course.
  47. M

    Newton's laws in polar coordinates

    I need explanation of these formulas for polar coordinate system where position of an object is characterized by 2 vectors: r - from the origin to the object, and Φ - perpendicular to r, in the direction of rotation. https://drive.google.com/file/d/0ByKDaNybBn_eakJmS3dUVXVZUDA/view?usp=sharing...
  48. M

    Explain speed limits on curved ramp with Newton's Laws

    Homework Statement Discuss how Newton’s Laws can be used to explain the introduction of transportation safety features such as: Speed Limits on curved ramps Homework Equations Newton's 2nd Law: F=ma The Attempt at a Solution I believe that according to Newton's first law objects that are in...
  49. J

    Circular Motion - Newton's Laws in different reference frames

    Homework Statement A child stands near the middle of a roundabout that is rotating with some angular velocity w. The child moves towards the edge of the roundabout in a straight line from the child's perspective and at constant speed. Explain in as much detail as you can (and using equations)...
  50. T

    Newton's Laws - Positive & negative direction

    Hi, While solving homework problems, I start by defining a positive-y direction and a positive-x direction. Let's say up and to the right. Until now, I've applied this same rule to all objects in each problem, no matter the direction the object moves. But it seems I have not understood this...
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