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. Elkay

    Another Newton's Law of Motion Problem.

    Due to a jaw injury, a patient must wear a strap (see the figure) that produces a net upward force of 5.00 N on his chin. The tension is the same throughout the strap. To what tension must the strap be adjusted to provide the necessary upward force? Here's the picture: I think the...
  2. R

    What is the reaction force when hammering a nail?

    1. Why is inertia called an inherent property? 2. According to third law of motion, specify the action and reaction while hammering a nail. Action is hammering but what's the reaction?
  3. R

    How Much Force to Stop a Car on a Dime?

    Homework Statement An advertisement claims that a particular automobile can "stop on a dime." What net force would actually be necessary to stop an automobile of mass m traveling initially at a speed of v in a distance equal to the diameter of a dime, which is d? Homework Equations F=ma...
  4. A

    Understanding Momentum Transfer as a Tensor in Newton's Law of Viscosity

    What does it mean by momentum transfer is not a vector (3 components) but rather a tensor (9 components)?
  5. L

    Some Questions Involving Newton's Law

    A skier starts from rest at the top of a 24 degree slope 1.3 km long. Neglecting friction, how long does it take to reach the bottom? At what angle should oyu tilt an air table to simulate motion on the moon's surface where g= 1/6 m/s/s? A block is launched up a frictionless ramp that...
  6. R

    Problems involving Newton's law

    these were the questions: 1.Heather can apply a force of 72 N to a wagon in which sits her little brother, Bryce. The combined mass of Bryce and the wagon is 48 kg. If starting from rest, how much speed will the wagon pick up after Heather has pushed the wagon for 3s? 2.When the wagon in...
  7. N

    Newton's Law of Cooling and Stefan's Law

    I am trying to relate an object temperature as a function of time using Stefan's Law. Newton's law of cooling is, \frac{dT}{dt}\; =\; k\left( T-R \right) Where T is temp, t is time, k is a constant, and R is the temperature of the surroundings. Stefan's Law is, P\; =\; e\sigma AT^{4}...
  8. A

    Newton's Law Problem (got the first half)

    I got the first half of this problem, I'm just stuck on the others. Please take your time to help Thanks a lot! Problem: A 5kg penguin sits on a 10kg sled. A horizontal force of 45 N is applied to the sled, but the penguin attempts to impede the motion by holding onto a cord attached to a...
  9. P

    What is the significance of the constant A in Newton's Law of Cooling equation?

    I have a question about Newton's Law of cooling. Basically I understand that the equation, http://album6.snapandshare.com/3936/45466/853596.jpg Comes from the DE, dT/dt = K(T-To) Using this, I am to solve this problem: A thermometer is taken from an inside room to the outside, where...
  10. M

    Action/reaction pair Newton's law

    hi i have a question if in a question, and they ask, action/reaction pair of the force lets say a man is swimming..and they say name the action/reaction pair of the force, of the force that causes the man to accelerate..how would i reply?
  11. A

    Some Newton's Law Questions: Understanding External Forces and Reactions

    I am having trouble with some of these questions: 1. A ball is held in a person's hand. a) Identify all the external forces acting on the ball and the reaction to each. b)If the ball is dropped, what force is exerted on it while it is failling? Identify the reaction force in this case...
  12. P

    Why Did I Get the Newton's Law Problem Wrong?

    Hi, I needed to calculate this for my quiz couple days ago, but I didn't get the right answer. Professor told me that I set it up correctly, so I don't understand why I got it wrong. Can anyone help? I resolved this problem, so I just need to verify the answer. Thanks Q: Block B, with mass...
  13. B

    How Does Adding Weight Affect the Distance a Cart Moves?

    A shopper in a supermarket pushes a loaded cart with a horizontal force of 13 N. The cart has a mass of 33 kg. (a) How far will it move in 3.0 s, starting from rest? (Ignore friction.) M (b) How far will it move in 3.0 s if the shopper places his 30 N child in the cart before he begins to...
  14. B

    What is the average force exerted by a punter on a football in Newton's Law?

    Well, I am having trouble with this and I been looking at the book for a long time and still lost. The teacher never went over this so no notes to help me out here either. A football punter accelerates a football from rest to a speed of 10 m/s during the time in which his toe is in contact...
  15. K

    Which Way Will the Spool Roll? Q&A on Newton's Law

    https://www.physicsforums.com/attachment.php?attachmentid=7470&stc=1&d=1155157461 spool.JPG Q: if the thread(see attach) is pulled in the direction shown, which way will the spool roll? i know that the spool will roll to the right according to Newton's law (for every action there's an equal...
  16. H

    Deriving Newton's Law of Gravitation: Understanding the Significance

    Newton's Law of Gravitation Derivative Hi, I was wondering if anyone could help me find the derivative of Newton's Law of gravitation [F=(GmM)/r^2] and what it means? What does the minus sign indicate? I'm kind of confused on the subject at hand and hopefully someone can help out. Thanks
  17. U

    Reading on Newton's law of universal gravitation

    i was doing some reading on Newton's law of universal gravitation. the equation is given as mass of 2 objects divided by distances square and then multiply by gravitation constant. using 50kg and 100 kg mass and a distance of 2 metres i get a value 8.34e-8 N this a small force, which sets me...
  18. Amith2006

    Is Newton's Law of Cooling Applicable to Forced Convection Losses?

    Sir, Can you state an example for forced convection loss? Is Newton’s law of cooling also applicable to forced convection losses apart from natural convection losses?
  19. C

    How long does it take for an object to cool using Newton's Law of Cooling?

    Hello, I am an undergrad student studying Physics. We are currently studying thermodynamics. The lecturer has set us a bunch of problems relating to Thermodynamics. While I can do most of them, I am getting completely thrown by one question: An object with a surface area of 0.2 m², an...
  20. homology

    Can Coffee Cool Below Room Temperature?

    Hey Folks, I was showing my students Newton's Law of cooling (precalc class) and one of my students pointed out that this doesn't really model the cooling of an object, he said that he had recently learned in chemistry that the temperature of the object that is cooling actually dips down...
  21. K

    Newton's law of motion problem

    Here is the problem. I think I set it up right but I am stumped now. An object with mass m1=5.00 kg rests on a frictionless horizontal table and is connected to a cable that passes over a pulley and is then fastened to a hanging object with mass m2=10.0 kg. Find the acceleration of each object...
  22. G01

    Newton's Law of Gravity and Potential Energy

    2 Jupiter sized planets are released 1.0 X 10^11 m What are their speeds as they crash together? I decided to try to do this problem with Potential Energy from Newtons law of gravity that is U_{g} = \frac{\-GMM}{r} I set the 0 of potential energy at the point when the planet's center's...
  23. S

    Newton's law of cooling of a surface

    I'm having trouble thinking of an instance when Newton's law of cooling is no longer valid. could it have something to do with the surface of the system or the surroundings not having uniform temperature. thanks very much
  24. S

    Newton's Law of Gravitation problem

    In Figure 13-34, a square of edge length 22.0 cm is formed by four spheres of masses m1 = 7.00 g, m2 = 3.50 g, m3 = 1.50 g, and m4 = 7.00 g. In unit-vector notation, what is the net gravitational force from them on a central sphere with mass m5 = 2.30 g? Okay this is what I did so far...
  25. T

    Newton's law problem have attempted it

    Newton's law problem...have attempted it http://img128.imageshack.us/img128/2941/asd6rh.jpg rope is of negligible mass and no friction...now this is what i did the bc and ab are subscripts for cords between each block 9.8(10)- Tbc = 10a 9.8(40)-Tab = 40a Tab=30a so by...
  26. S

    Newton's law and two blocks on vertical inclined plane

    hi i have a question: if you have 2 blocks on a vertical inclined plane... ( with angle teta = pi/2) what would m1 be equal to for a1 and a2 to be = 0 (the answer should be in terms of some or all of the variables of m2 and g) thanks
  27. R

    How Do You Apply Newton's Law to Solve Incline Problems?

    well, my question isn't directly towards Newton's law or anythiing, but its a question on how to solve problems using Newton's law. for example, look at this problem below.. a force of 20N acts horizontally on a mass of 10kg being pushed up a fritionless incline that makes a 30degrees angle...
  28. D

    How Does Newton's Law of Gravitation Influence Modern Physics?

    :smile: Dirac.
  29. C

    Newton's Law of Cooling Problem

    I did a problem where I was asked to model a simple cooling graph. No big deal. I got my model and found my constant values by using initial values. Now comes the sticky part. I am asked to create a model similar to the previous simple cooling problem for a more complex system. Keep in...
  30. P

    Isaac Newton's Theory of Gravitation

    Does anyone know the proof for Newton's law of gravity, because i looked in a lot of books for this proof but i didn't find it anywhere! Slowly I'm getting a little cautious about what we're easily accepting in school! Thanks for your reply.
  31. 4

    Calculating Velocity and Time Using Newton's Second Law

    A sled of 6.0 kg mass is moving along a smooth, horizontal ice surface with a velocity of X. A force of 36N is applied to the sled in its direction of motion, increasing its velocity to 2X while it moves 10m. Find the sled's original velocity, x. And the length of time that the force acted...
  32. P

    Newton's Law of Cooling on cup of coffee

    A cup of coffee at 174 degrees is poured into a mug and left in a room at 76 degrees. After 5 minutes, the coffee is 134 degrees. Assume that the differential equation describing Newton's Law of Cooling is (in this case) dT/dt = k(T-76) here's what i done: y(0) = 98e^{kt} y(5) = 134-76...
  33. P

    What is the Formula for Newton's Law of Cooling?

    I am stumped on one question out of twenty on my lab report. T = T0e-kt + Troom When T = 0 what is the value of e to the negative kt
  34. I

    How Do I Apply F=ma to Solve These Physics Problems?

    Hey, i been trying to ask all my friends and trying to read the book over and over. I am having problems with physics, its really hard! I have some questions that I am stuck at. I got the basics that F=ma but can someone help me get which equations to use for these questions? Thank you, i have...
  35. S

    Experiencing Newton's Law: Why Do Passengers Jerk Forward?

    Not sure exactly: 1. Why do passengers jerk forward when the car suddenly stops? I know it is somethin' relative to Newton's law but I don't know which law it is and how it actually happens. and 2. Why do the passengers feel like they are pushed to the outside of a turn.
  36. S

    Another Newton's Law Question.

    Question: A force of 50N acting at 37degrees above the horizontal pulss a block along the floor with constant velocity. If the coefficient of friction between the blocck and the floor is 0.2, what is the mass of the block? the answer in the book is 23.4kg but when I did it I got 20.3kg...
  37. S

    Discovering Horizontal Acceleration: Newton's Law Question Solved

    I'm really stumped with this question. A block is held against the front of a vertical wall of a railroud car. The coeffiecient of friction between the block and the wall is 0.4. When the train betgins to accelerate the block is released and begins to slide down the wall with an...
  38. N

    Which Newton's law describes inertia is proportional to mass?

    1.Which Newton's law describes inertia is proportional to mass? 1st or 2nd? 2.An object is on a slope, the graph of v-t shows that there is negative acceleration, how do you explain it ?
  39. N

    Newton's Law Help: Solving for Acceleration & Force in a Pulley System

    Hi, I have been given this problem to do as extra credit: An inventive child named Pat wants to reach an apple in a tree without climbing the tree. Sitting in a chair connected to a rope that passes over a frictionless pulley, Pat pulls on the loose end of the rope with such a force that the...
  40. N

    Solving Newton's Law: Calculating Acceleration and Force in a Pulley System

    Hi, I have been given this problem to do as extra credit: An inventive child named Pat wants to reach an apple in a tree without climbing the tree. Sitting in a chair connected to a rope that passes over a frictionless pulley, Pat pulls on the loose end of the rope with such a force that the...
  41. S

    Calculating Relative Acceleration and Velocity with Newton's Law of Gravity

    Two particles having masses of m and M respectively, attract each other according to Newton's law of gravity. Initially they are at rest at an infinite distance apart. Find their relative acceleration and show that their relative velocity of approach is v(rel) = square root(2G(M+m)/a)...
  42. maverick280857

    Newton's Law of Cooling and Stefan's Law

    Hello I've been thinking about this for a while and having consulted quite a few resources on the internet, decided to post some issues related to heat transfer by forced convection/radiation here... Stefan's Law states that the rate of heat transfer by radiation from the body to the...
  43. B

    How Do You Solve Complex Physics Problems Involving Newton's Laws?

    These problems are really giving me fits, I would really appreciate some help. A 12200 kg sailboat experiences an eastward force of 27400 N due to tide pushing its hull while the wind pushes the sails with a force of 56200 N directed toward the northwest (45± westward of North or 45±...
  44. M

    Finding Surface area using Newton's Law

    As part of a homework assignment, I am required to research Newton's Law of Cooling and evaluate it with three practical examples. One must be time of death. So far i have created a time of death example, and used an example to cool food. However the last one i heard someone say is that you...
  45. M

    Newton's Law of Cooling formula

    Im having a bit of trouble using Newton's Law of cooling. I have been given the formula T(t)=T_s + (T_0 - T_s) e^{-kt} . I am trying to find the time of death of a body, and I am given the time the body was found 12.00pm, its temp around 90, 2nd check, at around 1.00pm, temp is 80, and the...
  46. M

    Newton's Law of Cooling Applications

    As part of my research, i have to find 3 pratical examples that Newtons Law of cooling can be used for. So far i have two, finding the time someone died, and cooling down soup. I have to find a third, which does not involve food, or someone dying. if anyone could suggest a good third practical...
  47. M

    Newton's Law of Cooling constant k

    In Newton's Law of Cooling, we have the constant k, i was just wondering (most people will prolly laugh at me) what the constant k represents, and what units this constant would have. Also, can the law describe a cold object being heated up in a warmer environment. Any help would be...
  48. N

    How Much Force Is Needed to Move an Object Up an Inclined Plane?

    hey guys! i need some help, a big help. this is urgent... can somebodyhelp me solve this problem: what force, applied parallel to the plane, is necessary to move a 16 kg object up africtionless palne with a uniform acceleration of 2.0 m/s2 if the plane makes an angle of 60 degrees with the...
  49. T

    Exploring Newton's Law of Cooling with Physics Project

    Hi everyone. I am doing a physic’s project about Newton’s law of cooling. This project was basically to evaluate the change in temperature between a cup of cooling water and the room temperature as a function of time by using different methods of heat retention (via convection & evaporation...
  50. N

    What prevents a star from collapsing under its own gravitational attraction?

    According to Newton's Law of Gravitation, all objects with mass attract one another. This law implies that all of the atoms that make up a star, such as our sun, are gravitationally attracted to one another. How is a star able to resist collapsing under its own gravitational attraction? [?]...
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