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. B

    Derivative of Newton's Law of Gravitation

    Homework Statement Newton's Law of Gravitation says that the magnitude (F) of the force exerted by a body of mass (m) on a body of mass (M) is F = (GmM)/(r^2) where G is the gravitational constant and r is the distance between the bodies. Find dF/dr and explain it's meaning. What...
  2. D

    HELP Derive Newton's Law of cooling

    Hey guys was hoping someone could give me a hint for the derivation of Newton's Law of cooling stated in the following equation form:http://img263.imageshack.us/img263/3143/a6e5a27835e9e5738016606.png http://img716.imageshack.us/img716/8728/75784887.jpg Thanks in advance!
  3. V

    Is there any way to prove Newton's law

    a Newton's law states that : F=m.a , but I realize that it belongs to our sense , but may be someone know more about this . if you have any explanation or proof , let me know :)
  4. G

    How to Solve a Newton's Law of Cooling Problem

    Homework Statement A thermometer is removed from a room where the air temperature is 20degree C and is taken outside where the temp is -10degree C. After 1 minute the thermometer reading is 3degree C. What is its reading after 3 minutes? Homework Equations The Attempt at a Solution...
  5. L

    Scalar potential in EM and Newton's Law

    Hi,all, problem is: in Electromagnetism, we introduced a scalar potential psi, such that: E = - grad Psi and In Newton's law, there is also a scar potential U, such that: F= -grad U My question is, one is the gradient of a scalar field give a field and a force?! Can anyone...
  6. S

    Help with Newton's Law of Gravitation

    1. Find the magnitude and direction of the net gravitational force on Mass A due to masses B and C in Figure 6.27. Each mass is 2.00 kg. The figure looks like this: A<----------->(10 cm distance)C<-------------------------->(40 cm distance)B 2.F(g)=G * (m(1)m(2))/(r^2) 3.I'm...
  7. R

    Newton's law of cooling from Stefan's law?

    I read it in my book that Newton's law of cooling can be derived from Stefan's law. Is it possible, and if so, how?
  8. M

    Newton's Law of Cooling Flawed?

    Newton's Law of Cooling (not the formal definition): (change in time) = -ln ((Tf - S)/(Ti - S)) / k Tf = final temperature Ti = initial temperature S = temperature of environment k = heat transfer coefficient Say that you wanted to cool something (such as a person) to a negative...
  9. A

    Calculate the constant in Newton's law of gravity

    Phobos, a moon of Mars, moving around planten in a circular orbit of radius 9,5\cdot 10^6. phobos period of revolution / orbital time is 7 h and 39 min. calculate the mass of March with the help of the given data and the constant in Newton's law of gravity. it is easy to calculate the mass in...
  10. V

    Newton's Law and Frictional Forces

    These are two word problems, so I don't think the template applies to this thread. 1. Two strong magnets are on opposite sides of a tabletop's surface so that the attraction between the magnets is all that is holding up the one underneath. Identify all forces which involve either magnet...
  11. C

    Two questions about Newton's law

    Homework Statement 9. A fisherman yanks a fish out of the water with an acceleration of 4.5 m/s^2 using very light fishing line that has a "test" value of 22N. The fisherman unfortunately loses the fish as the line snaps. What can you say about the mass of the fish? A. m > 1.5 kg...
  12. M

    Newton's law of cooling

    Homework Statement A hot metal rod is placed in a water bath whose temperature is 40F. The rod cools from 300F to 200F in 1 minute. How long will it take for the rod to cool to 150F? Homework Equations The Attempt at a Solution I know y'=-k(y-T0) and y(t) = T0 + Ce^-kt and i...
  13. B

    Divergence of Newton's law of gravitation

    I am studying vector calculus, and I saw the following result in a physics text: g = -\frac{m}{r^3}\vec{r} r^2 = x^2 + y^2 + z^2 \vec{r} = ix + jy +kz \nabla \cdot g = 0 I'm not sure how this was done. Is the product rule used somehow? What happened to the extra power of r...
  14. C

    Newton's law of cooling and thermometer

    Homework Statement Hi, I need some help in solving Newton's law of cooling problem. Use Newton’s law of cooling to determine the reading on a thermometer 5 min after it is taken from an oven at 72 ◦ C to the outdoors where the temperature is 20 ◦ C, if the reading dropped to 48 ◦ C after...
  15. C

    Newton's Law of Gravity question

    Homework Statement An astronaut lands on an unknown planet with a radius of 3560 m. When she jumps upward with an initial speed of 3.00m/s she rises to a height of 0.50 m. What is the mass of the planet? Homework Equations vf2 = v02 + 2a\DeltaX The Attempt at a Solution In...
  16. P

    Dimensions of Newton's Law of Gravitation and Coloumb's Law

    As we know, Newton's Law of Gravitation is \[ {\mathbf{F}} = \frac{{Gm_1 m_2 }} {{r^2 }} \] and Coulomb's law is \[ {\mathbf{F}} = \frac{{Qq_1 q_2 }} {{r^2 }} \] We know from comparing the dimensions of the first equation that G, the gravitational constant, has the dimension \[ [M^{ - 1}...
  17. R

    Calculating Force to Accelerate 6.3 kg Object at 44 m/s in 35s

    A 6.3 kg object is accelerated from rest to speed at 44 m/s in 35s. What average force was exerted on the object during the period of acceleration? Answer in units of N. i did f=mg so f=61.75 then i divided by 35 and i got 1.764 N. is that correct? whats the velocity for then? Thank...
  18. K

    A puck slides a total of 12m: Problem relating kinteic friction to Newton's law

    Homework Statement In a shuffleboard game, the puck slides a total of 12 m before coming to rest. If the coefficient of kinetic friction between the puck and board is 0.28, what was the initial speed of the puck? Homework Equations f=ma fk=U*N vf^2=v^2+2ad a=delta v/t The...
  19. M

    Newton's Law on Circular Motion

    Homework Statement Block mass "m" is sliding on frictionless horizontal surface while traveling inside of hoop radius "R". Coefficient of f between block and wall is "u", therefore, speed of block is decreasing. In terms of "R", "v, block's veloc.", "m", and "u", find expressions for: 1...
  20. A

    Newton's Law of Cooling of coffee

    Homework Statement Suppose that a cup of hot coffee at a temperature of 1850 is set down to cool in a room where the temperature is kept at 700. What is the temperature of the coffee 10 minutes later? Homework Equations f(t)=(T0 - T1))e-kt + T1 where T0 is the initial temperature of the...
  21. M

    How Do You Calculate Acceleration in a Two-Block System with Friction?

    Newton's Law of Motion problem! Help please! Homework Statement A small block of mass m1 is placed on block 2 of mass m2 this is then placed on the table. A string connecting block 2 to a hanging mass M passes over a pulley attached to one end of the table. The mass and friction of the pulley...
  22. PrincePhoenix

    Is Newton's Law of Gravitation Flawed?

    What are the problems in Newton's law of universal gravitation? Please explain using simple physics if possible.
  23. C

    Newton's law of cooling and your body

    Homework Statement a body has temperature 27C at twelve oclock. The room temperature is constant at 16C. Two hours later the body was found to have a temperature of 24C. The temperature of a normal human body is 37C.Using Newton's law of cooling estimate the time of death. Homework...
  24. M

    Newton's Law of Motion Problem, HELP :'(

    Homework Statement Assume a 8-passenger learjet has a force of gravity of 66000 N [down] acting on it as it travels at a constant velocity of 640 km/hr [W]. if the forward thrust provided by the engines is 13000 N [W], determine: a - the upward life force on the plane b - the force due to...
  25. P

    Equilibrium applications of Newton's law of motion II

    Box 1 is resting on the table with box 2 resting on top of box 1. a massless rope passes over a massless, frictionless pulley. One end of the rope is connected to box and the other end is connected to box 3. The weights of the three boxes are w1=55.0N, W2=25.7N. Determine the mangitude of the...
  26. P

    Equilibrium applications of Newton's law of motion

    A supertanker with the mass of 1.72 *10^8 kg is moving with a constant velocity. Its engines generate a forward thrust of 5.52*10^4 N. Determine (a) the magnitude of the resistive force exerted on the tanker by the water and (b) the magnitude of the upward buoyant force exerted on the tanker by...
  27. S

    Hi two phys prob about Newton's law

    http://www.webassign.net/sercp/p4-62alt.gif (Figure P4.62) Three objects are connected by light strings as shown in Figure P4.62. The string connecting the m1 = 5.00 kg mass and the m2 = 4.00 kg mass passes over a light frictionless pulley. a) find the acceleration of each object and b) the...
  28. S

    Is Newton's Second Law the Definition of Force and Mass?

    hi guys, I just wonder that do we really need the law I? since that law II, because of F=ma, you need a F such that there exist a a somehow that I heard that it is related to frames, but I didn't quite understand, would anyone here be kind enough to elaborate a bit please?
  29. J

    How Do You Calculate the Masses in a Two-Block System with a Tension of 18 N?

    Homework Statement Two masses are joined together by a massless, inextensible string. A vertical force of 30 N applied to the upper mass gives the system a constant upward acceleration of 3.2 m/s^2. If the tension in the connecting string is 18 N, what is the smaller of two masses? If the...
  30. T

    Why is Newton's law of gravitation different for non-spherical objects?

    Hi there, I don't understand why the equal of Newton's law of gravitation F = Gm1m2/d(squared) is different for no spherical objects. In the image of my attachment there are one spherical object and a no spherical object. So why if there are not very distant the equal used is F =...
  31. A

    Newton's Law Homework Question

    Newton's Law Homework Question! Question: Peter and John are playing a game of tug-of-war on a frictionless, icy surface. Peter weighs 539 N and John weighs 392 N. During the course of the game, John accelerates toward Peter at a rate of 3.0m/s^2. a) What is the magnitude of the force that...
  32. B

    Newton's law of universal gravitation

    Hi all, Does Newton's law of universal gravitation depend on the geometry of the manifold? For example, what happens to formulas if we take the projective plane as our universe? How can one model "the mass" on the projective plane or on torus? I am a math grad with very elementary...
  33. G

    How does the GR field equation reduce to Newton's law of gravity?

    I've never taken a class on GR, but I've been looking at books on the subject. Clearly, Einstein's equations for GR must reduce to Newton's law of gravity, but how? I haven't seen it worked out anywhere. Can someone send me a link, or show a proof or derivation? Like I said, it's not...
  34. V

    Mechanics doubt in Newton's Law of Motion.

    Question-1. An engine of mass 105 tonnes is coupled to and pulls a carriage of mass 30 tonnes.The resistance to the motion of the engine is 1/100th of its weight.The resistance to the motion of the carriage is 1/150th of its weight.If the tractive force exerted by the engine is 25750 Newton.The...
  35. S

    Newton's Law Problem: Calculating Acceleration on an Inclined Plane

    Homework Statement A block of mass m1=2.0 kg on a frictionless inclined plane of angle 20 degrees is connected by a rope over a pulley to another block of mass m2=1.0kg. What are the magnitude and direction of the acceleration of the second block? Homework Equations...
  36. I

    Newton's law trick? question

    Newton's law "trick?" question Homework Statement A 40 kg girl and a 50 kg boy are on the surface of a frozen lake, 10 m apart. Using a rope, the girl exerts a horizontal 5.0 N force on the boy, pulling him toward her. Calculate the magnitude of the girl's acceleration.Homework Equations F=ma...
  37. R

    Newton's law conceptual question

    1. Homework Statement [/b] The force you exert on the Earth is insignificant compared to the force the Earth exerts on you. (True or false) The attempt at a solution[/b] I believe that this is false based upon Newton's third law--shouldn't the forces be equal and opposite? 2. Ice...
  38. M

    Newton's Law of Cooling. little question about 'Specific heat' of Mercury

    Newton's Law of Cooling Time Required to Cool (or heat) an Object [Also known as Newton's Law of Cooling] t=mCp(Ts-Tf)/Q Where; Q is the heat added (or being removed) from the object in watts m is the mass (weight) of the object in Kg Cp is the Specific heat of the object...
  39. F

    Newton's Law Question Involving Tow Truck

    Homework Statement A tow truck pulls on a stuck car with a force of 3000N. The tow cable is under tension and pulls downward and to the left on the pin at its upper end. The pin is held in equilibrium by forces exerted by 2 bars A and B which are connected to the pin. The diagram shows...
  40. J

    Newton's Law of Cooling problem

    Homework Statement The temperature T of a cup of coffee is a function T(t) where t is the time in minutes. The room temperature is 20 ^\circ Celsius. The rate at which the coffee cools down is proportional to the difference between the temperature of the coffee and the room temperature. Use...
  41. science_rules

    What is the Formula for Determining Height in Newton's Law of Gravitation?

    Homework Statement Starting with Newton's law of gravitation, determine the height h one person has to go from the surface of Earth in order for the person's weight to be reduced to 1/5 of their weight at the surface of the Earth. The only information you are given is that the radius of the...
  42. B

    Using Newton's law of cooling

    a cup of coffee is heated to 100° then left in a room with a constant temperature of 68° after a minute the temperature of the coffee has dropped to 95° after another minute to 92 degrees. how much time must pass before the temperature of the coffee has dropped to 70°?
  43. M

    Newton's Law Friction Problem

    Ok, I was watching a physics lecture and there was an interesting example given Heres the Example "A rubber tire has a static coefficient of one, so at an angle of 45 degrees, the car will start to slide, which is independent of the area of the tires and mass of the car." So i did the...
  44. S

    Newton's law and conservation of linear momentum

    Conservation of linear momentum is consequence of which one of Newton's three laws?
  45. DaTario

    First Newton's Law: Why Only Two?

    Hi All, This point was raised by a professor friend of mine, in an examination for entering MsC on science education. Why three laws for mechanics if the first law (inertia) can be derived as a particular case of the second (F = ma) ? We should have only two laws. Thak you All...
  46. P

    Newton's law of cooling

    Homework Statement If you remove a glass of iced tea from the refrigerator, and leave it sitting on the table in a room with temperature 25 C, then Newton’s Law of Temperature Change gives the temperature of the tea after t minutes as f(t) = 25 − Ce−kt where C and k are constants...
  47. A

    Understand Newton's law of universal gravitation

    Homework Statement http://i241.photobucket.com/albums/ff4/alg5045/1012540B.jpg Consider the Earth following its nearly circular orbit (dashed curve) about the sun. The Earth has mass 5.98 *10^24 kg and the sun has mass 1.99 *10^30 kg. They are separated, center to center, by r=93 million...
  48. ?

    Newton's Law of Motion for a Straight Line Motion

    Homework Statement An oil tanker's engines have broken down, and the wind is blowing the tanker straight toward a reef at a constant speed of 1.5 m/s. When the tanker is 500 m from the reef, the wind dies down just as the engineer gets the engines going again. The rudder is stuck, so the only...
  49. ?

    Newton's Law of Motion for a Straight Line Motion

    Homework Statement An oil tanker's engines have broken down, and the wind is blowing the tanker straight toward a reef at a constant speed of 1.5 m/s. When the tanker is 500 m from the reef, the wind dies down just as the engineer gets the engines going again. The rudder is stuck, so the only...
  50. W

    Acceleration of 3.8kg Object: 110.58 m/s2, 28.66°

    Only two forces act on an object (mass= 3.8 kg). One force is pointing east with 40 N. The other has a force of 75.0 N at a 45 degree angle. Find the magnitude and direction (relative to the x-axis) of the acceleration of the object. pythagorean theorum tan O= opp/adj x...
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