# What is Newton law: Definition and 50 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. ### I A question on momentum conservation of bodies in combined motion

Frictions are neglected in the system pictured. Here, a 1kg object released from above moves the car underneath. When this object falls off the car, what is its speed in m/s? This question was asked from momentum conservation, but I didn't want to do it from there. Can you solve the question...
2. ### Feynman's Lectures exercise about Newton's laws

TL;DR Summary: Solutions to an exercise coming from the famous "Exercises for the Feynman lectures on physics". I'm stuck on an exercise. "A mass ##m## (kg) hangs on a cord suspended from an elevator which is descending with an acceleration of ##0.1g##. What is the tension T in the cord in...
3. ### I Origin of Centripetal force when the net force toward the center is 0?

to clarify , my purpose isn't to find a solution to my home work , I already did the home work and my thread is more a request of justification or at least a clarification of the forces at play. I need explanation on the general topic not the solution to my question, I am mentioning the question...
4. ### I Spring balance analysis from a system point of view

Hi, I was thinking about a simple scenario in the framework of Newton (classic) mechanics. Take a spring scale/balance fixed at one end (wall) with a body attached to the other end's hook. From an analysis point of view we can consider as "system" the spring scale + the wall + the body. Then...
5. ### I When does the instantaneous velocity exist?

The instantaneous velocity at time a is defined as derivative of motion function f(t). It is not similar to average velocity in an interval of time. From the Newton law. If an object is at rest, we must exert a force to make it move, assume that there is no friction. Depend on the weight of...
6. ### 3 pulley problem with attached masses

in the opposite problem that has three pulleys and two masses, the book is asking for : 1- the tension on the string. 2- the acceleration of pulley p1. 3- the acceleration of mass m2. 4- what should the mass "m" be such that m1 does not accelerate? note : pulley p1 has mass m, in the diagram of...
7. ### Explain what laws of physics were violated in this scenario....

Homework Statement From reliable information, once Baron Münchhausen was stuck in a swamp, he pulled himself out of it by the hair. What laws of physics did the baron break? (Find the answer analytically) Homework Equations None. The Attempt at a Solution Well, I think that he breaks the...
8. ### Why is the normal reaction force zero in the absence of any external force?

Homework Statement My question is not a homework problem. I am having difficulty in understanding the concept oof contact forces. Homework Equations What I don't understand is that when two bodies A and B are in contact and left on a frictionless surface, they apply normal reactions on each...
9. ### Vector addition and Newton's law

I know that n-body problem can be complicated, but that's for the dynamics. What about a static case: e.g. if I have the distances of several bodies A, B and C etc. and their distance to a reference mass m, can I just use the vector addition of the Newton's gravitational force to add up all of...
10. ### Finding the direction of the force knowing the mu static

1. A crate resting on a rough horizontal floor is to be moved horizontally. The coefficient of static friction is 0.40. To start the crate moving with the least possible applied force, in what direction should the force be applied? a. Horizontal b. 24 degrees below horizontal c. 22 degrees...
11. K

### Force exerted on a chain of wagons pushed by a car..

Imagine a car that weights 1000Kg. Its engine pushes it forward with a force of 3kN. So the car is accelerating at 3m/s^2 (imagine there are no friction). After 100 seconds (the speed of car at that moment is 300m/s, very realistic), the car hits a wagon that weighs 1000Kg, that is on rest. And...
12. N

### Explaining acceleration due to gravity without math

Hi, I teach a physics class to a group of homeschooled students. Many of them aren't yet at the level of algebra. Last week we went over Newton's laws and did some experiments to show objects fall at the same rate regardless of mass. One student though, has asked me to explain why the mass...
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### Two Questions on Newton Law Problems

These are conceptual questions, and i just want to really understand why the answer is the answer! 1. Homework Statement 1) A force acts to push two boxes, box 1 and box 2, across a floor (assume for this problem that friction is negligible). The two boxes are stacked such that the force...
14. ### Is true force just "accepted" if it satisfies Newton law?

So I understand the relationship between mass x acceleration=force but all that relationship tells me is "Whatever the force is to accelerate a given mass at a specific unit of acceleration = units of force, and we just accept whatever the unit of force is. example 1/ms² x 1 kg mass = 1 N...
15. ### What is the work done by friction in a sliding and rolling ring?

Homework Statement A uniform ring of mass m and radius r is projected horizontally with velocity v on a rough horizontal floor,so that it starts off with a pure sliding motion and it acquires a pure rolling motion after moving a distance d.If the coeffcient of friction between ground and ring...
16. ### Friction of rubber box on concrete floor

Homework Statement A 10 kg rubber box is resting on a concrete floor. A force of 200 N is then applied to this box in a horizontal direction. What is the magnitude of the friction force on the box? Homework Equations This is a question about applying Newton's laws so Fsmax = μs η and η = mg...
17. ### MHB Find General Form of Z & T: Newton's Law of Cooling

A cup of tea is removed from the fridge and left on a desk. The temperature of the room is constantly E and T(t) represents the temperature of the tea after t minutes. dT/dt = K(E-T) Z(t) = E-T(t) How do I find the general form of Z and T?
18. ### Calculating the tension in rope of accelerating object

I have attached a picture so that it is easier to visualize this problem. The information is all in it. The number scribbles are just my attempts to solve it: http://i65.tinypic.com/2qlbn9h.jpg The current topic we are on in class is Newton's Laws and we have covered moments and equilibrium...
19. ### Initial acceleration of the charge

Homework Statement Three identical charged balls of mass m and charge q bound in a triangle thread length l. One of the strands break. Calculate the acceleration of the middle ball at the initial moment. 2. Relevant equation a. Newton's laws ##m\vec a_1 = \vec F_{12} +\vec F_{13} + \vec...
20. ### Can you merge these equations and get acceleration

m*a=k*Q1*Q2/r equalizing Newton's first law and coulomb's force to get acceleration of the specific charged body.
21. ### Why are the forces in Newton's 3 laws equal, but not in hydraulic systems?

Hi Mentor i am in little confusing about force, according Newton third law force on action and reaction is equal but according hydraulic system are not equal. https://www.facebook.com/photo.php?fbid=1749685448591067&set=pb.100006488851023.-2207520000.1429362639.&type=3&theater Thank you for...
22. ### Question about Third Newton Law

If I jump, I accelerate away from Earth. However, if I drop a human on the ground, he doesn't accelerate away from the Earth. In both cases the force used on the Earth is about the same, but acceleration away from the Earth exists in one case and doesn't exist in another case. Why so? (not a...
23. ### Newton law of universal gravitation

Homework Statement Having problems on the method of calculating the acceleration due to gravity of the planet. A certain planet has a diameter of 1715 km and a density of 5254 kg/m³. The planet has a moon that orbits every 4.46 earth-days. What is the acceleration due to gravity...
24. ### Does Newton's Law of Gravitation Apply in Outer Space?

Hello I studied about the Newton law of Gravitation which states that in universe every matter attract each other with a force which is denoted by F= Gm1m2/r^2. But in my view it is only happen within the region of gravity of a matter. but not in the space. please can anybody help me in...
25. ### Newton law, An object hanged with a robe that has a weight.

Homework Statement An object 50kg is hanged with a wire that wights 12,2kg Homework Equations what's the tension in the robe The Attempt at a Solution W - T = 0 (50+12,2)* 9,81 = 0 T = 610.182 N
26. ### Newton's Second Law: Solving for Acceleration and Velocity | Homework Help

Homework Statement http://postimage.org/image/810vdcuvf/ Homework Equations F=ma The Attempt at a Solution for part a) i put mdv/dt = -F(brake) - kv but is lost for what to put in for part b), help?
27. ### Newton Law Gravitation - Multiple choice question?

Newton Law Gravitation - Multiple choice question?? Homework Statement Newton’s law of gravitation can be applied to the Earth-Moon system. Which of the following statements is not correct? A The value of G at the surface of the Moon is the same as that at the surface of the Earth...
28. ### How Do You Calculate Initial Temperature Using Newton's Law of Cooling?

A hot object cools down to a temperature of 10 degrees of Celsius during a period of 180 seconds. The room temperature is 10 degrees of Celsius. Assume the coefficient in the Newton's Law of cooling to be 0.01[1/sec]. Determine the original temperature of the substance 2. T(room) +...
29. ### Having trouble finding the tension of this Newton law problem

Block A in the figure below has mass mA = 4.5 kg and is sliding down the ramp. Block B has mass mB = 2.2 kg. The coefficient of kinetic friction between block B and the horizontal plane is 0.50. The inclined plane is frictionless and at angle 30°. part a is to find the tension the equation...
30. ### Newton law Applications. Any suggestion

A mass M at To =0 s has a speed of lVol in the positive X direction. The floor has a coefficient of static friction of Us and a coefficient of kinetic friction of Uk. How far will the mass M travel? mass = M @ To = 0s speed = Vo coefficient of static friction = Us coefficient of Kinetic...
31. ### 2nd and 3rd Newton Law Problem

Consider the figure below where the coefficient of kinetic friction between the m1= 2.0-kg and the m2 = 3.0-kg blocks is 0.30. The hanging mass is given to be m3 =10.0-kg and the horizontal surface supporting the blocks along with the pulleys are...
32. ### Solving Newton's Laws of Motion Problems - Step-by-Step Guide

I'm having some difficulty with some sample questions. I have the solution to the problems. but i don't know how to work through the problem to get to the solution. 1.what is the mass of the object? details: Two strings are holding up an object. string 1 is 30 degree and 23N. string 2...
33. ### Another Newton law theoroy question

Homework Statement pushing an armchair across a carpeted or at constant speed v you apply a force of 100N if you push same chair at constant speed 2v(twice as fast) you mush push with a force? a)100N B)141N The Attempt at a Solution Newtons second law? if the net force acting on...
34. ### Entropic force correction to Newton law by Modesto and Randono

The paper is impressive. I'll get the link. Here http://arxiv.org/abs/1003.1998 On our 2nd quarter 2010 MIP ("most important paper") poll, I noticed that Atyy picked both of the Randono papers. It made me think about this one, that came out in March---the first quarter of 2010, so not on the...
35. ### Newton's Laws: Force, Time, Acceleration, & Distance

A 4kg block rests on a table. 5N is applied to it, pulling it the right, giving it an acceleration of 1ms^-2. ( a)If the applied force acts on the block for 5s, what will be the speed of the block at the end of this 5s be? (b)After 5s, the applied force is removed. What will be the new...
36. ### How Do You Solve for Acceleration and Tension in a Pulley System?

Homework Statement http://img69.imageshack.us/img69/2429/phyq1.jpg Homework Equations to find the acceleration of the 2 objects and the Tension Force. The Attempt at a Solution since only 1 pulley used, a=a1=a2, then m1a=T (1) m2a=-T+m2gsin45 (2) i...
37. ### Calculating Arrow Speed with Doubled Force | Newton's Law Problem

Homework Statement An arrow, starting from rest, leaves the bow with a speed of 29.5 m/s. If the average force exerted on the arrow by the bow were doubled, all else remaining the same, with what speed would the arrow leave the bow? Homework Equations use a= v-vo/t and f=ma The...
38. ### Calculating Net Force on Boxes of Different Masses in Contact

Homework Statement Two boxes full of books are in contact with each other on a smooth table. Box H has twice the mass of Box G. If you push on box G with a horizontal force F, then box H will expereince a net force of? Homework Equations F =ma The Attempt at a Solution answer from...
39. ### Bernoulli Equation and Newton Law

Hello friends, I have a problem in Bernoulli equation and Newton Law. I'm going to calculate how much power is needed to lift up an object with weight W. I'm planning to put the object in a 10 inches diameter. How can I calculate the power needed by the motor to lift up the object? Does...
40. ### Could we rewrite the Newton law

Could we rewrite the Newton law as F=G\rho\rho1\frac{}{} d^{}2? I' ve read this in a book. Is it right?
41. ### What is the Tension on a Spring Scale for an Object on an Incline?

Homework Statement I am trying to understand how these Newton's laws work, specifically with an object on an incline. If a 5.00kg object is attached to a Newton spring scale on an incline (incline makes 30 degrees with the ground), what reading is the scale giving? Homework Equations Fx...
42. ### Max Weight for Newton Law Problem Homework

Homework Statement If the maximum tension either rope can sustaine without breaking is 5000N determine the maximum value of the hanging weight that these ropes can safetly support. the diagram shows two ropes connecting at a node which leads down to a weight, the first rope on the left is...
43. ### Max Height of 2kg Object in Newton Law Problem

[b]1. "two objects with masses 5kg and 2kg hang .6 m above the floor from the ends of a cord 6m long passing over a frictionless pulley. Both objects start from rest. Find the maximum height reached by the 2kg object. Homework Equations Newton's laws. Kinematic equations. The...
44. ### Newton's Laws: Solving Friction Problems with Applied Force and Net Force

An applied force of 50 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of friction. Use the diagram to determine the normal force, the net force, the mass, and the acceleration of the object. (Neglect air resistance.) this is the image she...
45. ### Force and Newton law of Motion

hi there i have a question in which i can't get the answer i will show my work on what i did, if anybody can help , that would help a lot . here is the question: only two forces act on an object (mass= 3kg) x=40N a=60N is at 45 degrees above the horizon y= ? find...
46. ### Calculating Force: Newton's Law and the Motion of a 850 kg Dragster

I need some help on the two questions: A 850 kg dragster, starting from rest, attains a speed of 24.6m/s in 0.49s. 1. What is the size of the average force on the dragster during this time interval? Do I just use the equation F=ma to find this answer?...because I found the acceleration...
47. ### How Can You Solve Problems Using Newton's Laws?

Does anyone know how to solve this?
48. ### Newton Law of Universal Gravitation

we all learn this law. It state that the force between two bodies of mass m_1 and m_2 is attractive in nature. The gravitational attraction F is directly proportional to the product of the masses of the two bodies and inversely proportional to the square of the distance between them. From the...