What is Newton's law: Definition and 351 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. T

    Effect of doubling a mass Newton's law of universal gravitation

    Homework Statement Particle A having mass mA is placed at a fixed distance r from particle B which has twice the mass of particle A. Which of the following statements will be true? Select one: a. The magnitude of the force on A will be twice the magnitude of the force on B. b. The...
  2. X

    Transforming Newton's Law of Universal Gravitation

    Hello, physicsforums. I'm trying to write a proof for a function involving Newton's law of gravitation, and I seem to be stuck. The function I'm trying to build is a function of time with respect to distance. This is the formula I want to transform. \mathrm{A}=-\frac{GM}{x^{2}} For...
  3. R

    Newton's law of gravity or Einstein's general theory of relativity?

    I don't know much about the two ideas but I'm confused because the two theories seem to contradict each other, if all matter (with mass) bends space, then there is no such thing as "gravity", or maybe gravity is just the actual bending of space, so should we refute the idea of "gravity"? or just...
  4. C

    Differential Eqns: Newton's Law of Cooling

    Homework Statement A hot solid body is immersed into a large body of water which is a 4 degrees C. After one hour the body's temperature is measured at 40 degrees C, after 2 hours at 15 degrees. Assuming that Newton's law of cooling applies and that the water body is mixed constantly and...
  5. L

    Newton's Law of Cooling and other Models

    Hello, In my Differential Equations class we are learning about modelling with first order differential equations. We learned that Newton's Law of Cooling breaks down when the temperature of the object is approaching the temperature of the room its in. You eventually get to a point where you...
  6. P

    Newton's law of universal gravitation

    Homework Statement A star of mass 5 × 10e30 kg is located at ‹ 7 × 10e12, 3 × 10e12, 0 › m. A planet of mass 4 × 10e24 kg is located at ‹ 5 × 10e12, 5 × 10e12, 0 › m and is moving with a velocity of ‹ 0.6 × 10e4, 1.4 × 10e4, 0 › m/s. A. During a time interval of 1x10e6 seconds, what is the...
  7. C

    A decent k value for Newton's law of cooling for water?

    A decent "k" value for Newton's law of cooling for water? Recently I've been trying to cool some water to a specific temperature from boiling. It doesn't have to be super accurate (within about 5° degrees Fahrenheit or 2° Celsius) but the only thermometer I have access to is just for ambient...
  8. MarkFL

    MHB No-One's question at Yahoo Answers regarding Newton's Law of Cooling

    Here is the question: I have posted a link there to this topic so the OP can see my work.
  9. Mr-R

    Understanding the Work Needed to Escape a Gravitational Pull

    Hello everyone, What does it mean if I integrate Newton's law of universal gravitation with respect to r. F= GMm/r^2 become 3GMm/r^3 . Is this the work needed to escape a gravitational pull ? Thank you
  10. W

    Derivation of Newton's Law of Universal Gravitation

    ##F = G \frac{ m_{1} m_{2}}{ r^{2} } ## Where does the formula come from? And why does it work that way? How would it relate to Newton's Second Law? ##F = ma## Using Newton's Second Law, is it possible to get the Law of Universal Gravitation?
  11. Saitama

    What Is the Reaction Force to Earth's Gravitational Pull on a Book?

    Homework Statement A book is at rest on a table. What is the "reaction" force according to Newton's third law to the gravitational force by the Earth on the book? (1)the normal force exerted by the table on the book (2)the normal force exerted by the table on the ground (3)the normal...
  12. N

    Newton's Law: sliding down a slope

    A snow sled, with total mass 80.0 kg, is lowered at constant speed down a slope of angle 60.0° with respect to the horizontal, for a distance d = 14.0 m. The coefficient of kinetic friction between the sled and the snow is 0.290. Note: g = 9.80 m s–2. 1. What is the work done by the friction...
  13. MarkFL

    MHB Sammy's question at Yahoo Answers regarding Newton's Law of Cooling

    Here is the question: I have posted a link there to this topic so the OP can find my work.
  14. MarkFL

    MHB Nano's question at Yahoo Answers regarding Newton's Law of Cooling

    Here is the question: I have posted a link there to this topic so the OP can see my work.
  15. 2

    Calculating Time of Death Using Newton's Law of Cooling

    Homework Statement In autumn 2011 a whale was stranded. Although the whale was already dead for some time and the ambient temperature is approximately constant at the freezing point was, the body temperature was inside lying on the beach of Wales on 21 November is still about 20 ° C...
  16. W

    Confirming Newton's Law Answer

    Homework Statement I tried solving the question below, but I get a different answer than any available inthe m multiple choice. Homework Equations Netwon's Second Law The Attempt at a Solution I get 82N. http://hyperphysics.phy-astr.gsu.edu/hbase/incpl2.html gives me 82N for the tension...
  17. sankalpmittal

    Question- Newton's Law of Cooling

    Homework Statement A hot body placed in the surrounding of temperature θo obeys Newton's law of cooling dθ/dt = -k(θ-θo), where k is any constant. Its temperature is θ1 at t=0. t is time. The specific heat capacity of body is "s" and its mass is "m". Find the time starting from t=0 in which...
  18. N

    What does 'k' in Newton's law of cooling represent?

    Newton's law of cooling says: Instantaneous rate of cooling = -k (Original temperature - Final temperature) But what does this 'k' mean? I know it depends on the nature of the surface; but what property does it correspond to? Is 'k' related to specific heat capacity? Does higher...
  19. M

    Newton's law to find acceleration

    Homework Statement A block of mass m lies on a surface thirty degrees above the horizontal. A force with a magnitude equal to twice the weight of the block pushes it uphill. If the coefficient of kinetic friction is 0.4, find the acceleration of the block. Homework Equations Newton's laws of...
  20. N

    Help with Newton's Law Acceleration Problem

    Homework Statement A dockworker applies a constant horizontal force of 83.0 to a block of ice on a smooth horizontal floor. The frictional force is negligible. The block starts from rest and moves a distance 10.0 in a time 5.30 . If the worker stops pushing at the end of 5.30 , how far...
  21. G

    Question about Newton's Law of Cooling

    Newton's law of cooking T(t)= Ta+(To-Ta ) e^(-kt) or search it up online for a cleaner formula. Anyways, what does the cooling constant k represent. What do larger or smaller values of k mean? Thanks
  22. N

    Forces Involved in an Electrical Motor According to Newton's Law

    Hi Everyone. I've been trying to build an electrical motor and would like know the method to actually calculate the forces exerted on several parts in the motor according to Newton's laws. I've attached some pictures and drawings of the motor I'm trying to build. There are two scenarios that...
  23. D

    Finding conservation of energy through Newton's Law.

    Homework Statement I'm devising a lab to find/prove the conservation of energy through one of Newton's laws. I can substitute variables when do the lab, but I need to design it first before I assign variables or data.Homework Equations K.E.(initial) + P.E(initial) = K.E.(final) + P.E.(final) X...
  24. B

    Newton's Law of Motion: Understand F=ma & 1st Law

    Hi, Newton's 2nd Law can study the motion of the objects in the case of zero net force: F = ma if F = 0 then a = 0 then v = constant, then the object is either at rest (v=0) or moving in uniform rectilinear motion. (Bold quantities are vectors). What is the point of Newton's first law as it...
  25. L

    Question on Newton's law of universal gravitation

    Homework Statement The force of gravity on a spacecraft some distance from Earth is 900 N. What will be the force of gravity on a spacecraft with twice the mass, at a distance from Earth’s centre that is as far?
  26. M

    Newton's Law of Temperature Change Differential

    I'm a bit confused as to what I do next with this problem. Consider the initial value problem \frac{dy}{dx} = a(y-b) where y(0) = y0 With a > 0, b = 0, it represents exponential growth, while a < 0, b = 0 gives exponential decay. With y = T, a = -k, k = TA and y0=T0 it gives Newton's Law of...
  27. W

    How to Calculate the Mass of the Second Skater in a Skating Duo?

    Homework Statement A 62-kg ice skater pushes off his partner and accelerates backwards at 1.8m/s2. If the partner accelerates in the opposite direction at 2.1m/s2, what is the mass of the other skater? Assume that frictional forces are negligible. Homework Equations F=maThe Attempt at a...
  28. D

    How Do You Calculate Tension in a Spinning String Loop?

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  29. H

    Angular velocity using Newton's law

    Homework Statement Small object of mass m is placed on the inner surface of the conical dish which can rotate with angular speed ω. For μ=0.3 calculate the minumum and the maximum ω such that the object is remains at rest. Solve the problem using the indicated axes x-y. Do the following...
  30. W

    Newton's Law of Cooling for Multilayers

    1. A problem that I need to solve for class is asking me to solve Newton's Law of Cooling for a 4-layered system. The system is a cube with three layers (also cubic) around it. The inside cube and the three layers all start at the same temperature that is lower than the ambient temperature...
  31. B

    Newton's Law of Cooling & Specific Heat Capacity

    Newton's Law of Cooling basically states (I believe): TObj = (TInital-TEnv)ekt + TEnv where k is a property of the material. In the equation: Q=mCΔT Specific heat capacity, C, is also a material property. So here's my question: Is there a relation between Newton's Law's k and the...
  32. P

    Newton's law in non inertial frame.

    Please explain the concept of pseudo forces by considering an example of two cars say A and B, accelerating in the same direction. How will Newton's law applied to the man in car B as noted by the man in car A differs from that of the man standing on the earth? And how will the man in car A...
  33. J

    Newton's Law of Cooling (Calculating Time of Death)

    Homework Statement The problem states that you discovered the body at 1pm Thursday in a freezer where the temperature was 10F. Temperature of the corpse at discovery was 40F. I have to find how many hours ago the victim died. Homework Equations You are given the formula T = Ta + (98.6 -...
  34. B

    Extreme Newton's Law of Cooling D.E.

    Homework Statement after a very unpleasant valentine's Day, a dead body was found in a downtown warehouse that had no heating or air conditioning. it was February in Florida and we know that the daily temperature in the warehouse fluctuates according to the function T(t)= 63-12sin(∏t/12)...
  35. M

    Newton's law of cooling question, no inital temperature given

    Homework Statement The temperature of an object has been lying at rest and cooling for sometime had been found to be 31oC. An hour later, the same object was found to be 30oC. The room was also What was the initial temperature of the object, assume Newton's law of cooling applies...
  36. W

    Newton's law of universal gravitation

    Homework Statement is there a point between the Earth and the moon for which the net gravitational force on an object is zero? Where is this point located? Note that the mass of the Earth is 5.98x10^24 kg, the mass of the moon is 7.35x10^22kg, and the distance between the centres of Earth...
  37. A

    Newton's law of cooling with multiple containers DE's

    I've been trying to figure out how to solve the following problem: "A metal bar is placed in a container (call it container A) which is inside of a much larger container (call it container B), whose temperature can be assumed to be constant. Find the function for the temperature of the metal...
  38. H

    Regression (I think) of Newton's Law of Cooling

    Homework Statement Using a data logger, I have collected data for two cooling cups: the temperature (c) at 1 second intervals. My task was to model this data using two methods. "METHOD 1: Use EXCEL or the regression analysis capability of your graphic calculator" "METHOD 2: Find the...
  39. T

    Newton's Law of cooling DE involving delicious coffee.

    I did this problem a few times now and double checked my procedure but I don't see what I did wrong. The answer should be 6.07 minutes according to the back of the book, but I get 3.63. Homework Statement Newton's law of cooling states that the temperature of an object changes at a rate...
  40. G

    Newton's Law of Cooling of object

    I don't understand Newtons law of cooling dT/dt = k(a - b) were a is the object and b is the surroundings that the object is placed in... Is this correct or is there suppose to be a negative sign like so dT/dt = -k(a - b) also does Newton's law of cooling apply to putting a cold object...
  41. G

    Newton's Law, tension, blocks, pulleys at an angle, friction

    Hi all, I'm really stumped at this question five of my assignment. Could anyone please give me some help? I don't even know where to start. Thanks
  42. I

    Basic Newton's Law Problem, 2 Blocks on a frictionless ramp/pulley

    Homework Statement Draw a free body diagram for the block on the frictionless ramp below. Break up any problem vectors into friendly vectors. Will you work in x and y components or parallel and perpendicular? Then, find the magnitude of each force you have labeled. Lastly, find the...
  43. J

    Newton's law with Cantor potential

    I want that [0,\infty[\to\mathbb{R}, t\mapsto x(t) satisfies \ddot{x}(t) = -\partial_x U(x) where U:\mathbb{R}\to\mathbb{R} is some potential function. Then I set the initial conditions x(0) < 0, \dot{x}(0)>0, and define U(x) = \left\{\begin{array}{ll} 0,&\quad x < 0\\ \textrm{Cantor...
  44. O

    How Did Newton Confirm His Law of Gravitation?

    I've worked out the inverse square law using centripetal acceleration and Kepler's law. But I can't quite see how Newton worked out for sure that the force is directly proportional to both masses. I know it's pretty intuitive, but I thought maybe there was a mathematical way of confirming that...
  45. O

    Newton's Law of Conservation- Based on a Fallacy?

    Do you ever lie awake at night worrying about natural laws? How can we 'focus on basic principles', or indeed 'clarify the nature of physical laws' by using a model that doesn't exist in nature?
  46. S

    Newton's Law of Motion: Surface Force Unaffected by Acceleration?

    What I want to ask is the (b) part (It's one of our old MTs). In the solution given, it talks about an acceleration,a3, on the horizontal axis. However, in the equation, the surface forces acting on m1 and m2, FN1 and FN2, are not affected by this acceleration, a3. Isn't that wrong?
  47. FeDeX_LaTeX

    The Inequality for e in Newton's Law of Restitution Collision?

    Homework Statement "A small smooth sphere of mass 3 kg moving on a smooth horizontal plane with a speed of 8 m/s collides directly with a sphere of mass 12 kg which is at rest. Given that the spheres move in opposite directions after the collision, obtain the inequality satisfied by e."...
  48. L

    Newton's law of cooling to find time of death

    URGENT! Newton's law of cooling to find time of death Homework Statement The victim, Peter Sloane (a senior physics lecturer), was discovered at 9.43pm with a liver temperature of 22.26°C in the Oliver Lodge coffee room, with the window open. The temperature of the room matched that of the...
  49. V

    Lorentz force and Newton's law

    Homework Statement This problem asks you to work out the dielectric function of a gas of particles with number density n, charge q, and mass m, with a steady magnetic field applied in the z direction. Assume an electric field in the x direction, E_x(t)=E_xe^{-i \omega t} is applied. Write...
  50. S

    Is it possible to use Newton's Law of Gravity AND Einstein's Theory of Gravity?

    to answer this question: Q) A mass of 100kg is 50m away from a mass of 250kg (from centre of masses). Calculate the gravitational force of attraction between both point masses. Could I use Einstein's theory of gravity to answer this question using the information given. If so, how would I...
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