What is Newton's laws: Definition and 478 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. V

    Friction -- Newton's laws of motion

    Homework Statement A student is cleaning a block board by moving a light duster up and down as shown. (Coefficient of friction between the duster and board is ##MU## The duster will not move no matter how large the force is if ? Homework Equations No equations given The Attempt at a Solution...
  2. V

    Newton's laws of motion -- finding the velocity of a Block in a pulley system

    Homework Statement Determine the speed with which block B rises in figures if the end of cord at A is pulled down with a speed of 2ms^-1 Homework Equations Given Velocity downwards at A=2m/s The Attempt at a Solution Really stuck... Couldn't even start the question solving...I know all...
  3. V

    Newton's laws of motion -- pulley system

    Homework Statement In the situation given all surfaces are friction less pulley is ideal and steering is light. Find accn of block 2 Homework Equations Given F=mg/2 The Attempt at a Solution .[/B] Got answer as G/2 instead of G/4 ...(actual answer is g/4) Since F=mg/2 and block 1 is hanging...
  4. V

    Newton's laws of motion -- Constaint motion

    Homework Statement In the following diagram a massless pulley is pulled by a constant force of magnitude P. There is no friction between the block and the floor. The acceleration produced in the block if mass m is? PIC ATTACHED Homework Equations Took a1/2=a2 where a1 is accn of block and a2...
  5. G

    How to find Kepler's law from Newton's laws

    We were asked to do an experiment where we had to prove the equation: T2=(4π2m)/Mgr Where M is the mass of the mass stack in kg (0.3kg), m is the mass of the rubber bung in kg (0.0226kg), T is the time taken for one rotation in seconds, r is the horizontal radius of rotation in meters, and g is...
  6. Shardul Khare

    Understanding Newton's Laws of Motion: Exploring Block Movement and Friction"

    When a keep two blocks one over another...And apply a foce on the block which is below...Why does the upper block falls down..Why dosent it move with A? assumin there's no friction between A and B?
  7. E

    The Normal Force on a Carousel: How Does it Affect Weighing Scales?

    Homework Statement [/B] A boy with a mass of m1 is sitting in a carousel. The spinning frequency is 0.3355. The boy is also sitting on a weighing scale, will they show a number higher than m1g,lower or the same? (The mass of the weighing scale is 0). Homework Equations mω2r=F ma=F ω2=4π2f2...
  8. G

    Combining Newton's Laws and Kinematic

    Homework Statement Max (65 kg) pushes Toni (50 kg) with a force of 360 N. The force of friction is 0 on Toni and 80 on Max. (a) Find each girls acceleration (b) If Max pushes Toni for 0.1 s, how far will Toni travel in 0.5 s? Homework Equations Fnet=ma v2=v1+at d=v1(t)+1/2a(t)^2 The Attempt...
  9. P

    How to apply Newton's laws to non-rigid bodies?

    Suppose we have a body of finite size which can be translated, rotated, compressed and stretched. We have every information about the body. We have its dimensions and everything. We have its mass and density. But, since I'm here talking about a completely generalized version, so we have variable...
  10. Mert Kerem Yavuz

    Applying Newton's Laws, motion with constant acceleration

    Homework Statement Homework Equations F=m*a ΣF=0 The Attempt at a Solution Firstly, I tried to work on the normal force of bowling ball. But I can't get the answer. I don't get the idea that bowling ball could be kept at constant height, I didn't really understand the question guess. Can...
  11. L

    Confusion about Newton's laws, sum of forces equals zero

    I've lately began working with Newtons laws problems at school again, and I've already ran into a few problems. When making calculations and solving problems, it is often nessecary to understand when forces are equal to zero, and when they are not. Since every force has an equal and opposite...
  12. Lauren0619

    Newton's Laws - Incline. Do I have the right idea?

    I am hoping that I can have someone look over my answers. I have provided what I think is necessary to be appropriate posting, including the questions and attempts at all my answers. I would just like some feedback that I am correct in my answers. Thank you! This is an overview that all the...
  13. Morrissey

    What are the reaction forces to the external forces on the wagon in (b)?

    Homework Statement One or more external forces are exerted on each object enclosed in a dashed box shown in the figures below. Identify the reaction to each of these forces, assuming that (b) occurs on Earth. Select all that apply. (b) the wagon exerts a force · downward on the Earth...
  14. DumSpiroSpero

    Mechanical Energy and Newton's Laws

    Homework Statement A block of mass ## m ##, attached to a rope, is dropped at the point A. When the block reaches the point B, the tension is ## T = 2 \cdot m \cdot g ## and the rope broke at that same point. If the length of the rope is ## L = 6cm ##, evaluate the height ## h ## where the...
  15. P

    B Orbital Mechanics: GR vs Newton's Laws

    9/1/2016 Orbital mechanics Wikipedia, the free encyclopedia This reference states: "General relativity is a more exact theory than Newton's laws for calculating orbits, and is sometimes necessary for greater accuracy or in highgravity situations (such as orbits close to the Sun)". Can GR...
  16. R

    Newton's laws and their implications on plain old geometry

    So, I'm reading a physics book, and it talks about Newton's three laws, of course, but then after that it says that if a force of f pushes on an object at angle Θ, then the force in the x direction is f ⋅ cos(Θ), and the force in the y direction is f ⋅ sin(Θ). Where did THAT come from? Do we...
  17. K

    Free-body diagrams and Newton's laws with a suspended chain

    Homework Statement The chain comprising three rings (each of mass ##0.25kg##) is suspended from a massless rope, and a pulling force ##\left(F=9N\right)## is exerted upwards on the rope. Picture: http://i.imgur.com/xeaiBsc.jpg?1. I need to find the values of all the unknowns. Homework...
  18. J

    Additivity of mass: provable from Newton's laws?

    Within the context of Newton's laws, it seems implicitly understood that mass is an additive property of objects. My question is: should this be considered "just" an experimentally confirmed fact, or is is provable from Newton's laws? The following is a more precise context for this question...
  19. Evangeline101

    Newton's Laws -- Resting hockey puck hit with a force

    Homework Statement A resting hockey puck is hit with a force of 15.3 N. The frictional force slowing the puck down is 1.0 N. a) Find the net horizontal force acting on the puck while the stick is in contact with the puck. b) If the puck leaves the stick with a velocity of 45 m/s, how far will...
  20. A

    Newton's laws of motion -- masses on pulleys....

    Homework Statement Wasnt able to upload file, therefore an external link https://drive.google.com/file/d/0B0FIIKckKOcKWFcxcmtJRVRXZTA/view?usp=drivesdk A force F= mg is applied on C, all pullies are frictionless and we need to find the reading of the spring balance, basically the tension...
  21. P

    Newton's laws -- Block sliding on a Prism

    Homework Statement All the surfaces shown in fig. are assumed to be frictionless. The block of mass m slides on the prism of mass M which in turn slides backwards on horizontal surface with acceleration of ao. Find the acceleration of smaller block with respect to prism. Homework...
  22. D

    How Does Adding a Cat Affect the Acceleration of a Block System?

    Homework Statement Consider the system shown in the figure (Figure 1) . Block A weighs 46.1 N and block B weighs 28.7 N . Once block B is set into downward motion, it descends at a constant speed. http://session.masteringphysics.com/problemAsset/1038576/6/YF-05-54.jpg A Calculate the...
  23. Ameer Bux

    Newton's Laws -- Your best tip

    Hi guys. I am planning to get 100 percent for my upcoming physics test in two days time. I am i grade 11. The test is based on Newtons 3 laws and universal law of gravitation. What are some of the best tips you can offer from your experience to help me achieve my goal?
  24. Cosmophile

    Are Newton's Laws Redundant or Fundamental?

    Hey, all. I've been studying Newton's Laws and I can't help but to feel a bit uneasy as I inspect them. From my point of view, they seem to be tautological. I'll refer to Newton's First Law as N1L, and similarly for the other two Right off the bat, I suppose I don't see any reason for N1L to...
  25. mcdavid&goliath

    Newton's laws multiple choice question

    Homework Statement A book of mass m is sitting on a table of mass M. Which of the following statements regarding Newton's Laws of motion is true? (a) Newton's Third Law says that the magnitude of the normal force from the table on the book is equal to mg. (b) Newton's Second Law says that the...
  26. S

    Newton's Laws: Impact, Orbit & Weight

    1. Which will have the greater force during impact; a bumble bee being hit by a train or a train being hit by a bumble bee? (Hint: Newton’s Three Laws of Motion) 1. What is the centripetal force that holds the Earth in orbit around the sun? 1. How much does a 76.0 kg person weigh on Earth in...
  27. G

    What is the accelerating force of a bullet in a 10cm gun barrel?

    Homework Statement [/B]A 10g bullet accelerates from rest to 500m/s in a gun barrel of length 10cm. Find the accelerating force (assuming it is constant).Homework Equations F=ma, v^2=vo^2+2a(x-xo)? The Attempt at a Solution I tried using F=ma, but it does not equal the answer in the back of...
  28. K

    Determining velocity for a pulley/rope system

    The Question: Using a simply pulley/rope system, a crewman on an Arctic expedition is trying to lower a 5.65-kg crate to the bottom of a steep ravine of height 23.9 meters. The 60.9-kg crewman is walking along holding the rope, being careful to lower the crate at a constant speed of 1.50 m/s...
  29. toboldlygo

    Does pushing down on a book increase the Normal force?

    So, I know that there is a Normal force exerted on the book by the table, and, according to Newton's Third Law, the book exerts a force onto the table. However, I have two questions: if I were to push down on the book, would that Normal force increase? What "creates" the Normal force? Is it the...
  30. toboldlygo

    Finding Tension in a Massless String on an Inclined Plane

    Homework Statement In the figure below, the objects are attached to spring balances calibrated in Newtons. Give the readings of the balances in each case, assuming that the strings are massless and the incline is frictionless. I need help with (d). If the picture's too grainy to read off...
  31. O

    Looking for worksheet (Newton's laws)

    Hey, Anyone know any good workshetts, pdf wise or a document with good questions about Newtons laws. What i mostly look for is, Incline plane questions, atwood machine questions with pulleys in different ways, half atwood machine questions. Etc. Very classical problems. Glad if U could help...
  32. DylanC.

    My Physics Professor says Newton's laws are wrong?

    My Physics Professor from my Physics 1 class says Newtons laws are wrong? Don't get me wrong, but he is a amazing physics professor! One that does not talk to you as if you are dumb or as if he is better than anyone! I love physics and I'm hoping to go into physics engineering, but that's not...
  33. S

    Newton's laws of motion problem -- Knife penetrating cardboard

    An open knife edge of mass 200 g is dropped from height 5 m on a cardboard. If the knife edge penetrates distance 2 m into the cardboard, the average resistance offered by the cardboard to the knife edge is:
  34. vinicius0197

    Deducing Kepler's second law from Newton's laws?

    I've searched a little bit and found that I can derive kepler's third law from Newton's law of gravitation. That's okay. But I want to deduce kepler's second law too: "An imaginary line joining a planet and the sun sweeps out an equal area of space in equal amounts of time". I know it's possible...
  35. A

    Center of mass and Newton's laws of motion

    Homework Statement two particles of 2 kg and 3 kg are at rest . a 6 N force is exerted on the 3 kg particle at t=0. what is the speed of the center of mass at t=5s? Homework Equations F=ma v=u+atThe Attempt at a Solution first i applied f=ma to the 3 kg object and got 2 as the accn. And...
  36. MARK 42

    No problem, glad I could help!

    In the arrangement shown in the figure, find the acceleration of M in upward direction. The pulleys are light. The strings are mass less and friction between the string and the pulleys is negligible. The options are given. The final answer is (B) and this was the solution: I don't...
  37. pinochet

    Acceleration of gravity and Newton's laws of motion

    hello I've just started learning physics my question is why do force increase while falling and stay constant while on the ground.i know force is increasing because in free fall things accelerate which according to Newton first law force must also go up. the force of gravity of Earth is 9.8N...
  38. wheels123

    Can you explain the lever using Newton's Laws?

    I have always thought that all of "Classical Mechanics" can be explained with Newton's Laws and a few force equations (e.g., gravitational and Coulomb). In particular, the concepts of energy and torque are convenient but not necessary. If this is true, then can you explain with Newton's Laws -...
  39. C

    Basic Newton's Laws and Applied Force: 3 boxes

    Homework Statement Three boxes are in contact with each other on a frictionless horizontal surface as shown. The masses of the boxes are m1 = 10 kg, m2 = 20 kg, and m3 = 30 kg. A horizontal force F = 90 N is applied to m1. Calculate: a. the acceleration of the three boxes. b. the net force on...
  40. C

    Question: Gravitational Potential Energy in a Ball-Earth-Moon system?

    Hello, here's a questions I was wondering if any of you could solve. I don't have the exact numbers, but the scenario is this: a guy standing on the Earth throws a ball upwards and catches it a few seconds later. How does would affect the potential energy and/or mechanical energy of the...
  41. K

    How Does the Monkey's Movement Affect the Box in a Pulley System?

    Homework Statement A monkey which has a mass of ##m## is hanging on a rope as the picture shows. Then the monkey starts to move upwards with speed ##u##. Find how the box which has a mass of ##2m## will move. Neglect friction between the rope and pulleys. Assume that pulleys are massless...
  42. AdityaDev

    How Does Acceleration Affect Spring Stretch in an Adiabatic Piston System?

    Homework Statement An adiabatic piston of mass m equally divides an insulated container of volume V0 and length l filled with Helium.The initial pressures on both sides of the piston is P0 and the piston is connected to a spring of constant k. The container starts moving with acceleration a...
  43. M

    How Do You Calculate Forces in a Multi-Block System with Friction?

    Three identical blocks are pushed across a table at constant speed. The hand pushes horizontally. Let the stack of two blocks be system A and the single block be system B. Now suppose the mass of each block is 2.5kg, the coefficient of kinetic friction between the bottom surfaces of the blocks...
  44. L

    Galilean Relativity and Newton's Laws

    I'm a little bit confused about the relationship between Galileo's Principle of Relativity and Newton's Laws. Indeed, as I understand, the Galilean Principle of Relativity is what Galileo presented with Salviatti's ship discussion. The discussion seems to lead to a simple idea: "if one performs...
  45. andro

    Analytical formulation of Newton's Laws

    Greetings historians of physics! Newton's Principia is written almost entirely using geometrical proofs and diagrams, barely using any calculus at all. It is thought that Newton was reluctant to use his calculus in this work, fearing that it would undermine its credibility and reception, since...
  46. F

    Why do we take component of v1 along the string in Newton's laws homework?

    Homework Statement Homework Equations None... Newton's laws The Attempt at a Solution Not the attempt, the entire solution is: String length is constant...hence if on the right side of the pulley, the string goes up by x distance then on the right side also the string goes down by x...
  47. K

    What is the man's upward acceleration when hoisting himself into a tree?

    Homework Statement To hoist himself into a tree, a 72 kg ties one end of a nylon rope around his waist and throws the other end over a branch of the tree. He then pulls downward on the free end of the rope with a force of 358 N . Neglect amy friction between the rope and the branch, and...
  48. K

    Forces and Newton's Laws of Motion

    Homework Statement The drawing shows a large cube (mass = 25 kg) being accelerated across a horizontal frictionless surface by a horizontal force P. A small cube (msmall = 4 kg) is in contact with the front surface of the large cube and will slide downward unless P is sufficiently large. The...
  49. E

    Calculating the Force Constant of a Bungee Cord Using Newton's Laws

    Homework Statement You've attached a bungee cord to a wagon and are using it to pull your little sister while you take her for a jaunt. The bungee's unstretched length is 1.3m and you happen to know that your little sister weighs 220N and the wagon weighs 75N. Crossing a street, you accelerate...
  50. B

    What Is the Minimal Tension Angle for a Mass Pulled Horizontally?

    Homework Statement Body of mass m is being pulled by a string so that it moves horizontally at constant speed. Friction coefficient between surface and body is u.Find an angle (alpha) between a string and horizontal surface for which tension in string is minimal and find that tension...
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