What is Newton's first law: Definition and 68 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. thomas_shvekher

    Newton's First Law to explain Washing Machine Spin Cycle

    I truly am not sure. I assume it is that because everything has inertia, an a tendency to remain in a constant state of motion, when the clothes are quickly spun around they cannot remain in a constant state of motion (of either rest or constant velocity), but the water is "pushed"/spun out of...
  2. Mikasun1108

    Newton's First law of motion -- Boy jumping vertically on a moving train

    I'm not sure if my answer is correct but I think the answer is false. Thank you for your help :) -sun1108
  3. E

    B Is Newton's first law of motion applicable when walking?

    Is Newton's first law of motion applicable when walking?
  4. jonander

    Newton's first law and a body on an infinite and frictionless road

    Hi everyone! I have started to study physics this month and I got to the Newton's laws. According to Wikipedia, the first law is: This definition made me wonder: If there was, let's say, a fictional road, infinite long and frictionless, and a body would move in constant velocity over it, could...
  5. D

    The Confusion of Weight and Mass in Physics Education

    In material introducing Newton's First Law to students, we sometimes see a supplementary statement to this effect: in addition to changing the velocity of an object, forces can distort its shape. But surely here two different situations are being conflated: (1) the effect of a single force on...
  6. Jehannum

    Is Newton's First Law a conservation law?

    I'm thinking through a few basic things - hopefully in a new way. One thing that struck me is that momentum (mv) and energy (e.g. 0.5mv^2) can be conserved but velocity is not. For one thing, velocity is relative, of course. I'm wondering whether there's a quantity a bit like velocity but not...
  7. Manny46

    What happens with the puck in a non inertial board?

    I'm not being extremely exact here, but suppose there's a puck in a board where there's very little friction. Both puck and board are at rest. Suppose the board starts from rest to some decent speed, so there's definitely this acceleration, by virtue of which (and also less friction), puck...
  8. R

    Newton's first law of motion and Inertial Systems

    I have just begun my journey in Classical Mechanics with the book "An Introduction to Mechanics" by Kleppner and Kolenkow. I find myself stuck at Newton's first law. The book presents Newton's first law as follows: "Newton's first law is an assertion that inertial frames exist." The book also...
  9. F

    Mathematical model of Newton's first law

    Is there a mathematic model for the first law of dynamics? If no, do you think that this law can be modellized with maths?
  10. Lunct

    Newton's First Law problem -- Conceptual question about KE

    I have come up with a bit of a problem in my head regarding Newton's first law. If any of you could help me solve it that would be much appreciated. So if you throw a tennis ball (or any object really), and you throw it into an infinite expanse of nothing but void, it will travel forever, or...
  11. Quantum Velocity

    Why do we have Newton's first law

    Hey guy! I know how Newton's first law said but i can't understand why. So can you pleas help and tell me why. Thank you!
  12. parshyaa

    Frame of reference in which Newton's first law is not valid

    Newtons first law of motion depends on frame of reference So what are some examples , which shows that in this frame of reference F = 0, but a is not equal to zero or vice versa.
  13. M

    How did Newton come up w/ 1st law? Why does friction exist?

    So I'm trying to understand Newton's laws, and I know that friction is supposed to be the force that stops an object in movement. But I don't really understand why this is the case, as the force of friction is not something that can be perceived intuitively (unlike, for example, the force I...
  14. Evangeline101

    Newton's First law: Barrier on large transport trucks

    Homework Statement Explain why large transport trucks have a hard steel barrier between the load and the driver's cab. Consider Newton's first law in your answer. Homework Equations no equations required.The Attempt at a Solution According to Newton’s first law, if no net force acts on an...
  15. alexandria

    Understanding Newton's First Law & Safety Measures for Roller Coaster Rides

    Homework Statement Homework Equations no formula's required The Attempt at a Solution please explain if these answers are correct, thanks 34. Large transport trucks have a hard steel barrier between the load and the driver’s cab In order to protect the driver and prevent injury. According...
  16. heartshapedbox

    Newton's first law, forces, charges

    Homework Statement Two uniform masses of .260kg are fixed at points A and B. Find the magnitude and direction of the initial acceleration of a uniform sphere with mass 0.01kg released from rest at point P that is acted on the gravitational forces of attraction from spheres A and B. The diagram...
  17. B

    Inertia: Internal Forces & Object Motion

    Homework Statement My textbook says that internal forces have no effect on an object's motion and that external forces are required to change the motion of an object. But, we looked at an expirement where a raw egg was spun and then stopped. After being stopped, it went back to spinning...
  18. P

    Inertial Frame of Reference vs Spacetime

    Is the inertial frame of reference the same thing as space time?
  19. L

    Question on Newton's first law

    An object with no resultant force can still be moving at constant velocity. Why? Is it because of its kinetic energy or has it got nothing to do with energy?
  20. J

    How can balanced forces result in constant velocity?

    Homework Statement Hi everyone. I am a grade 11 physics teacher. This week, I will be teaching about Newton's first law in class. I'm having trouble explaining one thing. Students generally understand that a hockey puck moving on ice will continue to move with constant velocity. In this case...
  21. RAHIL008

    Why can't a rocket continue to travel without fuel?

    By Newton's first law of motion, every object will continue to be in state of movement or rest, until acted upon by external force. Now, why can't a rocket continue to travel after it was initially thrusted (do not know if its right word) by fuel ? like a satellite that is set in orbit with some...
  22. S

    (simple) Applying constant force - Newton's first Law

    Another silly question... Assuming a surface with no friction in space (you get the idea), I push/kick/give a 1kg block on this horizontal plane a force of 1N. It would start to accelerate in the direction i pushed it with at a rate of 1m/s² forever until another force acted upon it. So far so...
  23. copypacer

    Newton's First law - Dropping a feather and a hammer....

    <<Mentor note: Edited for language>> 1. Homework Statement If I have a feather and a hammer and drop it at the same time from the same height (with out air resistance, so basically in a vacuum) Why would it land on the ground at the exact same time? Homework Equations F = ma The Attempt at...
  24. Rwindsor1

    Trouble with definition of Newton's First Law

    The lecturer in my dynamics class defined Newton's First Law to be 'There exists at least one inertial frame with respect to which mass m moves in a straight line with a constant velocity. In this frame no net force acts on m.' This has confused me; I thought inertial frames could not...
  25. M

    How does an object maintain constant velocity according to Newton's First Law?

    Newton's first law says that when an object is at rest or moving in constant velocity, it will stay that way unless external force is applied. So, net force is zero. What I don't get is on an object moving in constant velocity. How is the object begin moving? Is netforce applied initially...
  26. S

    Conceptual Newton's Law's Questions - HS Freshman Physics

    NOTE: The following questions are not part of any homework assigned. This is part of finding extra concept-related questions to help me study for my physics unit test. Homework Statement I have conceptual questions, not problems. I'll provide sufficient evidence that I've attempted to think...
  27. tomo

    2 questions regarding circular motion and Newton's 1st Law

    Hey, I'm an adult who finally realized that physics is great and tries to recall (or rather learn for the first time) what he learned at the school. I've been reading some basic things around. It's not really a homework question, I'm just trying to understand the laws here. 1. I know that if a...
  28. avito009

    Newton's First Law: Movement in Space Without Friction

    Everything should move in a straight line if there is no friction. But when an aircraft goes into space it needs to move burning its fuel. Why does it not move constantly in straight line? So is the reason behind the fact that a rocket needs to be propelled, that the gravity of the sun and...
  29. V

    Newton's First law and KT of Gases

    One of the assumptions of Kinetic Theory states that: A gas is a substance composed of many particles flying about randomly, colliding with one another and with the walls of the container. My instructor mention that we might be required to Know, state, and apply this theory to one of newtoms...
  30. L

    Newton's First Law: At Rest or In Motion?

    For Newton's first law, which one is correct? 1. All objects that are at rest, stay at rest; all objects that are in motion stay in motion, unless acted upon an unbalanced force. Or 2. All objects that are at rest, stay at rest; all objects that are in motion stay in motion, unless acted...
  31. M

    Understanding Newton's First Law of Motion in Physics

    Won't the sentence be complete if its mentioned, with respect whom the particle remains at rest or moves with constant velocity?
  32. Adjoint

    Why do we need Newton's First law? And how the First law works?

    This must have been asked before. But never mind here I ask it again to convince myself. Newton's Second law says \vec{F} = m\vec{a} Now if we put \vec{F} = 0 here we get \vec{a} = 0 which is Newton's First law. So why do we need to state First law as a separate law? Before I asked this I did...
  33. M

    Why is using Newton's First Law failing me?

    A factory worker pushes a 29.7kg crate a distance of 5.0m along a level floor at constant velocity by pushing downward at an angle of 32∘ below the horizontal. The coefficient of kinetic friction between the crate and floor is 0.24. What magnitude of force must the worker apply to move the...
  34. E

    Newton's first law and projectiles questions

    I just don't get these questions...please help. () are what I think the answers are but I am not positive. Question set 1: Beginning from rest, Mia Edwards runs the 200 meter dash with an acceleration of 0.9 m/s2. 1. define inertia. (inertia- the tendency of an object to resist change)...
  35. N

    Newton's First Law of Motion is Wrong (Proven Wrong in This Thread)

    Please note this is a very serious thread. Please note Newton's First Law: First law: When viewed in an inertial reference frame, an object either remains at rest or moves at a constant velocity, unless acted upon by an external force. Here is an experiment to prove this First Law...
  36. C

    Question about Newton's first law

    Homework Statement Q13 All external forces on a body cancel out. Which statement must be correct? A The body does not move. B The momentum of the body remains unchanged. C The speed of the body remains unchanged. D The total energy of the body remains unchanged. Homework EquationsThe Attempt...
  37. F

    Why Does Susan Fall Forward When the Metro Brakes?

    Homework Statement Susan is standing in an empty Metro (subway) car which is traveling at constant velocity. Suddenly, because of an emergency, the driver applies the brakes. Select True or False for each of the following statements. a) If she immediately grabs onto the seat behind her (she...
  38. adjacent

    Newton's 1st Law: Object at Constant Speed, No Reaction Force

    An object is traveling at constant speed.There is no force on it(It means it won't also exert any force on any object)What will happen if I put something in its path?If it does not exert a force there will be no reaction force(Newtons 3rd law).Then what will happen to it?
  39. E

    Question relating Newton's First Law of motion

    Hi there! I kept on reading my textbook and i found one simple confusion in Newton's First law of motion. I want to consider a situation where a space shuttle is moving in the outerspace (assume there is no gravity) under the influence of the engines. What will happen when the engine stops...
  40. R

    Slight confusion concerning Newton's first law

    Hi, I've very recently begun physics self-teaching as I used to find it boring and thus avoided it as a subject but now find it increasingly interesting. Nevertheless, I'm having some problems regarding questions on Newton's First Law. One of the questions in the book I'm using says the...
  41. P

    Perpetual motion and Newton's first law

    This might be a very stupid question. But let me still ask. :) Perpetual motion is not possible. But by Newton's first law, a body remains in its state of motion unless an external force acts on it. Now, I wonder if the statement "perpetual motion is not possible" is true only in a practical...
  42. W

    Apparent Discrepancy Between Two Definitions of Newton's First Law

    So I was reading through my textbook (specifically, Physics for Scientists and Engineers, Eighth Edition, Volume 1 by Raymond A. Serway and John W. Jewett Jr.) and I noticed that, in one of the "Pitfall Prevention" sections (which are usually quite helpful - not this time, evidently), it says...
  43. L

    How Does Spontaneous Decay Relate to Newton's First Law?

    Homework Statement Newton's first law of motion deals with inertia of bodies. According to this law, " Every body continues in its state of rest or of uniform motion in straight line, unless compelled by an external force." Homework Equations The Attempt at a Solution My question...
  44. C

    Where Does the Energy Come From for Motion Without External Forces?

    Forgive me if I'm missing a basic concept, A body does have a natural tendency to move, but a body does need energy to move! Where does this energy come from when no external force is applied on it? Please help, I've been pondering over this doubt since a week..
  45. H

    Is Newton's first law a particular case of the second?

    There is not much to explain my question, really. First law says that the velocity of a body remains constant if there is no external force acting, which is just equivalent to second law, as a null force is equivalent to null acceleration, as mass cannot be null.
  46. A

    What is Force in Newtonian Mechanics & Newton's First Law?

    Is Newton's first law the definition of force in Newtonian mechanics? If not: 1) What is the definition of force in Newtonian mechanics? 2) What is the purpose of Newton's first law?
  47. L

    On Newton's First Law of Motion

    This question is probably really stupid but I have to ask. I take a pot of water and stir it. This creates a vortex. When I stop stirring, the water continues spinning before slowing to a stop. But Newton's First Law says that "Every body persists in its state of being at rest or of moving...
  48. L

    Newton's First Law Explained: Ball Dropped From Moving Ship

    A ball released from the top of the mast of a moving ship lands at the base of the mast. Explain this according to Newtons' first law. I just know that the first law is that if the net force acting on an object is zero, the object will maintain its state of rest or constant velocity. How does...
  49. L

    Danger of Driving Too Fast on Icy Highway Curve: Newton's 1st Law

    Apply Newton's First Law of Motion to explain the danger in driving too quickly on a curve of an icy highway. I just know that the first law is that if the net force acting on an object is zero, the object will maintain its state of rest or constant velocity. How does it apply to this scenario?
  50. D

    What is the true nature of rest according to Newton's first law?

    HI, I have a stupid question but important, Newton;s first law doesn't mention anything about Net force , just that a body that no external forces acts in him, will stay @ rest or with constant velocity ,now my problem is the word "rest", Is a body at rest relative to something Is a body that...