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

    Circular motion and Newton's law question

    [b]1. A 78.0 kg man weighs himself at the north pole and at the equator. Which scale reading is higher? By how much? 2. I think that this has to do with with the radius being different at the north pole and equator, which would cause different centripetal accelerations. So I assume I'm...
  2. D

    Newton's Law of Acceleration

    Homework Statement A 10.0-kg mass on a frictionless table is accelerated by a 5.0-kg mass hanging from a table. Calculate the acceleration of the mass on the table. (It gives a picture but I can draw it if nobody can picture the diagram). Homework Equations F=ma F=mg The Attempt at a Solution...
  3. rocomath

    Calculating Time of Death Using Newton's Law of Cooling

    So I have a slight problem since I'm getting a negative for time. A murder victim is discovered at midnight and the temperature of the body is recorded at 31C. One hour later, the temperature of the body is 29C. Assume that the surrounding air temperature remains constant at 21C. a)...
  4. T

    Newton's Law of Cooling with no Ambient Temperature

    This is a 4 part ordinary differential equation problem. a.) You are a member of a CSI team that has discovered a dead body in a field. Upon discovery of the body you measure its temperature and find that it is 76.04058181\circF. 10 minutes later the temperature of the body is...
  5. C

    Calculating Elevator Acceleration and Velocity?

    Homework Statement "A student whose weight is 500 Newtons stands on a scale in an elevator and records the scale reading as a function of time. The data is shown in the graph above. At time t=0, the elevator is at displacement x=0 with velocity v=0. Assume that the positive directions for...
  6. L

    Newton's Laws: Exploring the Basics

    When 2 cars crash into the other, the smaller one skids backwards more than the larger one. - third law? Grandmother is very tired after rolling the bread dough on her kitchen table.- second law? After a while, airport runways show evidence of dark lines as tires are worn down from...
  7. B

    Newton's Law of Gravitation (again)

    Homework Statement a). Four particles, each of mass m , are situated at the vertices of a regular tetrahedron of side a. Find the Gravational force exerted on anyone of the particles by the other three b) Three uniform rigid spheres of mass M and radius a are placed on a horizontal table and...
  8. 2

    Newton's Law of Cooling equation

    Problem From Newton's Law of Cooling, we can use the differential equation dT/dt= -k(T-Ts) where Ts is the surrounding temperature, k is a positive constant, and T is the temperature. Let \tau be the time at which the initial temperature difference T0-Ts has been reduced by half. Find...
  9. B

    Problem concernng Newton's Law of Gravitation

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  10. T

    Elevator Physics- Newton's Law of Motion

    Homework Statement why is it that you sometimes feel 'light' or 'heavy' while moving in a fast moving lift? A lift has a total maximum mass, including occupants of 1000kg. it is supported by steel ables. the maximum acceleration or deceleration of the lift in operation is 2.0ms^-2. How big is...
  11. T

    Roller Coaster physics- Newton's Law of motions

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  12. Q

    How Does Newton's Third Law Apply to Forces in an Elevator?

    Hi. Let's say I have a lift with a man in it. The lift is moving upwards, and the forces acting on the man if I am not wrong is R (Normal reaction force by floor on man) and weight (mg). Hence R-mg=ma. Correct me if I am wrong or anything. But my teacher says that (this is a marking point...
  13. S

    What laws of motion are involved in the girl's fall while jogging in the park?

    One day a girl jogging in the park, doesn't see a sign up ahead, hits it and falls to the ground. Which of Newton's 3 laws is involved in this story? I think that Newton's 1st and 3rd law are invovled, not sure about the 2nd.
  14. T

    Explaining Gun Recoil Using Newton's Second Law

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  15. T

    Understanding Newton's Laws of Motion: Explaining Car Movement

    Homework Statement Why do you lunge forward when your car suddenly stops? Why are you thrown backwards when your car suddenly accelerates? Explain using Newton's laws Homework Equations ? The Attempt at a Solution Because of your seat belt, you are attached to the car, causing...
  16. L

    How High Could a Person Jump on Pluto Compared to Earth?

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  17. D

    Newton's Law of Cooling

    Homework Statement A small object of unknown temperature was placed in a large room that had the fixed temperature 30 degrees C. After 10 minutes, the object's temperature is -10 degrees C, and after an additional 10 minutes, the object's temperature was -5 degrees C. What was the initial...
  18. N

    Newton's law of gravitational attraction help?

    [SOLVED] Newton's law of gravitational attraction help? Homework Statement M1 is a spherical mass (38.6 kg) at the origin. M2 is also a spherical mass (10.3 kg) and is located on the x-axis at x = 61.2 m. At what value of x would a third mass with a 15.0 kg mass experience no net...
  19. B

    Newton's Law & Gravitational F: Finding the Accl'n for a sphere

    Homework Statement Three uniform spheres are located at the corners of an equilateral triangle. Each side of the triangle has a length of 1.20m. Two of the spheres have a mass of 2.8 kg, each. The third sphere has an unknown mass, and is released from rest. Considering only the...
  20. B

    What is the speed of the bus?

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  21. C

    What is the tension in cable 1 for a hanging chandelier?

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  22. C

    Newton's law of universal gravitation

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  23. J

    Deriving the Potential Energy Contribution of an Infinitesimal Mass on a Sphere

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  24. E

    Newton's law of cooling problem: Differential Eq

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  25. H

    Is the Second Hint for Newton's Law of Restitution Correct?

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  26. marcus

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  27. C

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  28. S

    A question about Newton's Law of Universal Gravitation

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  29. L

    Newton's Laws of Motion: Translation & Angular Forms, Assumptions & Equivalence

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  30. B

    Newton's Law of Gravitation ratio

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  31. K

    Newton's law of cooling and temperature

    at 1 pm, a thermometer reading 70 F is taken outside where the air temperature is -10F (ten below zero). at 1:02 p.m., the reading is 26F. At 1:05 p., the thermometer is taken back indoors , where the air is at 70 F. What is the temperature reading at 1:09 pm? Ive made a table like this...
  32. M

    Newton's Law of Universal Gravitation deflection

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  33. G

    Acceleration (Newton's law)

    Homework Statement A bureau rests on a rough horizontal surface ( mk=0.40, ms=0.50). A constant horizontal force, just sufficient to start the bureau in motion, is then applied.The acceleration of the bureau is: Homework Equations F= ma The Attempt at a Solution The answer is...
  34. S

    What is the difference between inertia and Newton's First Law?

    I'm taking my first Physics course (it's a foreign language), and in English class we were given a piece of paper on Skating taken from an English Physics textbook. We are having problems with some expressions, such as Inertia. What the heck is inertia? Is it a law? Or an expression? (I checked...
  35. D

    Newton's Law of Cooling of porridge

    Homework Statement A smaller bowl of porridge served at 200 degres F cools to 160 degres in 1 min. What tempature (too cold) will this porridge be when the bowl of exercise 27 has reached 120 degres F (just right)? Homework Equations y(prime)(t)=k((y(t)-T sub a ) y(t)=Ae^(kt)+T sub a...
  36. T

    Application of Newton's Law

    A race car travels 44m/s around a banked (45degree with the horizontal) circular (radius = 200m) track. What is the magnitude of the resultant force in N on the 80 kg driver of this car. I've having a hard time setting up the free body diagram. First I broke into Fx and Fy Fx: F...
  37. E

    Understanding Newton's Law of Universal Gravitation

    "Consider the Earth following its nearly circular orbit about the sun. The Earth has a mass mearth=5.98x10^24kg and the sun has mass msu=1.99x10^30kg. They are separated, center to center, by r=93 million miles = 150 million km." What is the size of the gravitational force acting on the Earth...
  38. J

    Newton's Law- 3 objects on a pulley

    Homework Statement 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 tension in the two strings...
  39. E

    Calculate Newton's Law Force to Keep Moon in Orbit

    Homework Statement The mass of the moon is 7.35 x 10^22 kg and its distance from the Earth is 3.84 x 10^5 km. Taking Earth's mass to be 5.98 x 10^24, calculate what Newton called "the force resquisite to keep the moon in her orb." mass of moon = 7.35 x 10^22 kg distance from earth= 3.84...
  40. S

    Newton's Law of gravitation using kepler's laws.

    Homework Statement Derive Newton's Law of gravitation using kepler's laws. Homework Equations Kepler's law equations. etc. The Attempt at a Solution l= r(1- e*cos(theta)) l- const. e- eccentricity Solving these equations using kepler's laws (r^2(d(theta)/dt), etc.)...
  41. M

    Heat equation w/ Newton's Law

    The equation given is \frac{\partial T}{\partial t} = \frac{\partial}{\partial x} \left( K(x) \frac{\partial T}{\partial x} \right), 0<x<L where T is temperature, t is time, and x is the 1-d spatial coordinate, also K(x) = \kappa e^{-x}, \kappa > 0 and the boundary conditions are...
  42. P

    Newton's law of cooling for corpse

    Homework Statement The time it takes for a deceased human body to reach room temperature. Room temperature = 25 degrees C Initial temperature of corpse = 37 degrees C Homework Equations I used Newton's law of cooling: \frac{dT}{dt} = -k(T - T_{room}) where T is a function of t(time in...
  43. E

    How Much Force Is Needed to Push a Piano Up a Ramp?

    Homework Statement A man pushing a piano with a mass 160kg at constant velocity up a ramp that is inclined at 36.9 degrees above the horizontal. Neglect friction. If the force applied by the man is parallel to the incline, calculate the magnitude of this force. Homework Equations The...
  44. E

    How Do Newton's Laws Apply to a System with a Heavy Rope?

    Homework Statement The two blocks are connected by a heavy uniform rope with a mass of 4.00kg. An upward force of 200N is applied as shown. a.) What is the acceleration of the system? b.) What is the tension at the top of the heavy rope? c.) What is the tension at the midpoint of the rope...
  45. T

    Questions on Newton's Law of Gravitation

    hi i have some questions about Newtons law of gravitation and i need complete answers coz these qwestion will be my second exam: 1.the gravitational force between a ring of raduis a and mass m and a rod of mass m and length l lies on the central axis of the ring and the distance is x between...
  46. A

    Newton's Law of Gravitation vs. Gravitational Potential Energy

    I'm confused about the two equations: PE_{G}=G\frac{m1*m2}{r} PE_{G}=mgh When do you use either of these equations? Can these two equations be used interchangeably or not? Also, I think I remember reading somewhere that you need to use the 1st equation when the problem involves large...
  47. S

    Newton's law of cooling

    Hey, I'm having problems with this question: According to Newton's law of cooling, what cools faster, a person from 150 degress celcius to 100 degrees celcius or 100 degrees celcius to 50 degrees celcius in a laboratory environment? Why? I' not really sure where to start. I know the...
  48. N

    Newton's Law of Cooling of pizza

    Homework Statement Bob loves vegetarian pizza. How long will it take Bob's pizza to cool to 110 degrees if he bakes it at 450 degrees for 20 minutes? The temperature in his house is a balmy 70 degrees. Homework Equations T(t) = Ts + Do*e^(-k*t) where... Do = initial temperature...
  49. wolram

    Why do we Still Believe in Newton's Law?

    http://arxiv.org/abs/gr-qc/0702009 Why do we Still Believe in Newton's Law ? Facts, Myths and Methods in Gravitational Physics Authors: Alexander Unzicker Comments: 29 pages LaTeX, 2 figures An overview of the experimental and observational status in gravitational physics is given, both...
  50. P

    Internal Forces and Acceleration: How Can We Stay with a Moving Block?

    Homework Statement Assume no friction. Suppose I exert a force of 1N to a block. The block will exert 1N of force back at me. If I keep exerting the 1N than there is a constant force of 1N exerted back at me so my hand is in constant velocity? But the block I am exerting the force is...
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