Newton's laws Definition and 478 Threads

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. Wajdi Al-ashi

    Do Newton's Laws Explain Motion and Inertia Anomalies?

    Q1: Are objects at rest or are they in a uniform motion along a straight line in the world and in the universe? Q2: Why does an object with an important inertia not move if I apply to it suddenly a big force (accelerate it rapidly)? And on the other hand, the same object does move with a small...
  2. K

    Inertial frame of reference question for stacked boxes

    Hello, I was wondering about a question and how it would be reconciled within Newton's laws of motion. Take a case where two boxes are stacked on top of each other, and the bottom box rests on a frictionless surface. Now, imagine a rope is attached to the top box, and tension is applied to...
  3. AdityaDev

    Understanding Buoyant Force: Exploring FBD and Equations in Accelerating Vessels

    If I have an object of mass m tied to the lower surface of a vessel having a liquid and the vessel accelerates upwards... From FBD of object, Buoyant force acts upwards, mg down, pseudo force downwards (frame of reference is vessel) T down. Here's the doubt. Why is F(buoyant force) = Vp(g+a)...
  4. S

    What is the acceleration of the crate?

    Problem: A 22.0-kg crate is pulled along a horizontal floor by the ideal arrangement shown in figure below. The force F is 300 N. The coefficient of friction between the crate and the floor is 0.270. What is the acceleration of the crate? Homework Equations F = ma Friction =...
  5. R

    Newton's laws question -- a car coasts to a stop on a level road

    Homework Statement A 1490 kg car is is traveling at a speed of 22.2 m/s when the driver let's the car coast on a level road. The friction on the car slowing it down is 288 N. How far will the car coast? Homework Equations f=maThe Attempt at a Solution i can find the force but i cannot find...
  6. GiantSheeps

    Finding Force on 7.7 kg Block in Contact with 9.2 kg Block | Physics Problem

    Homework Statement Three blocks in contact with each other are pushed across a rough horizontal surface by a 98 N force as shown. The acceleration of gravity is 9.8 m/s^2. ----F--->|2kg| |7.7kg| |9.2kg| u = 0.082If the coefficient of kinetic friction between each of the blocks and...
  7. D

    What Is the Minimum Hanging Mass Required to Keep a Block Stationary on a Wedge?

    1. A 1 kg wedge is pulled across a rough floor (uk=0.20) via contact with a 2 kg block as shown below. The shape of the wedge is that of an isosceles right triangle. a rope passes from the 2 kg block and over a mass-less and friction-less pulley and is attached to a hanging mass. Find the...
  8. J

    No, this is not correct. See my previous post.

    Homework Statement A truck (1200kg) is traveling south at 22m/s a) what is the net force required to bring the truck to a stop in 330m? b) what is the cause of this net force? (im assuming the answer is friction due to brakes) Mass= 1200kg (1.2*10^4) Velocity= 22m/s [south] What force is...
  9. A

    What if Newton's laws were shifted by one time derivative?

    What would be some important properties of a universe where Force = Mass * Jerk and objects stay in constant acceleration until acted upon by a net force? (if we ignore the fact that objects would reach the speed of light, and just deal with classical mechanics)
  10. L

    Why does a skateboard move backward when you push on it, but the Earth does not?

    Use Newton's to explain : When you take a step, you push down and back on the Earth and the Earth pushes up and forward on you. When you step on a skateboeard, the skateboard moves backward as you push down and back. Why does the skateboard move backward while the Earth does not even if the...
  11. J

    Newton's Laws Conceptual Problem

    Homework Statement "Normally, jet engines push air out the back of the engine, resulting in forward thrust, but commercial aircraft often have thrust reversers that can change the direction of the ejected air, sending it forward." "When might thrust reversers be useful in practice? (Chose all...
  12. I

    Newton's Laws of Motion Question

    Homework Statement A cart of mass 1.5 kg is connected by a string over a pulley to a hanging mass of 300g. What would be the acceleration of the cart and mass if the force of gravity is approximately 1N for a 100g mass. Cart 1=1.5kg Cart 2=0.3 Kg Fg1=15N Fg2=3N Homework Equations F=ma The...
  13. M

    Newton's Laws of Motion (Is my theory correct?)

    Homework Statement If two cars of equal mass are pushed apart by a spring mounted on cart #1 with a force of 14 N what will be the resulting acceleration of the carts. Mass of carts 1 and 2= 2.0Kg f=14N A? Homework Equations F=ma The Attempt at a Solution My theory is that the Newtons will...
  14. PhysicsHelp152

    Magnitude of a ball's Acceleration

    Homework Statement A 0.17-kg cue ball rests on the pool table. It's struck by a cue stick applying force F1→ = 13Ni^+21Nj^ Determine the magnitude of the ball's acceleration. Homework Equations ax = Fnet, x / m ay = Fnet, y / m a = Fnet / m The Attempt at a Solution Components of...
  15. K

    Newton's laws during a tug of war

    Homework Statement Adam and Ben pull hand over hand on opposite sides of a rope while standing on a frictionless pond. Adam's mass: 75.0kg Ben's mass: 50.0kg Adam's acceleration: 1.00 m/s2 to the east What is the magnitude and direction of Ben's acceleration?
  16. T

    Using Newton's laws to find an expression for the angle of inclination

    Homework Statement Use Netwon's laws to find an expression for the angle of incilination theta at which the refrigerator starts to slide. Express your answer in terms of possible g, Us, Uk and m. Homework Equations Fnet=ma Ff=UFn The Attempt at a Solution I attached my attempt...
  17. A

    Help Midterm tomorrow Pulley, Newton's Laws Problem

    1. Homework Statement An object consists of 3 connected masses as seen in the figure. None of the surfaces have friction except the surface on m1 which has the coefficients μs=0.4 y μk=0.3. What is the acceleration of each one of the masses? It looks like the following image but m1 is the...
  18. Govind_Balaji

    I need to do a project for science fair based on Newton's laws

    The science fair is after 1-2 months but I should submit a report not exceeding 300 words what I will do in the project tomorrow morning to my teacher. Now it's 10pm. Please give me ideas as soon as possible(Before 30min from now)
  19. G

    Newton's Laws applied at an incline including a spring and friction

    Dear Helpers, I'm sitting since ours in front of a task and trying to solve it. Attached you find a picture to the problem. Given: θ=28° μs=0.4 μk=0.3 k=30N/m m1=1kg m2=2kg x0=0 x1=1m --> Spring is stretched The question is: Does m2 move up or downwards? First thing I tried...
  20. Coffee_

    I don't understand the ''definition/law'' aspect of Newton's laws

    Hello everyone, it's been a while since I've been introduced to Newton's laws for the first time. Yesterday I've been reading the Feynman lectures vol 1, where Feynman makes a remark about Newton's laws not really containing any physics. This got me thinking and I'm really confused right now...
  21. Q

    How Do You Calculate Force on an Inclined Plane with and without Friction?

    Homework Statement A 90 kg box is pushed by a horizontal force F at constant speed up a ramp inclined at 28°, as shown. Determine the magnitude of the applied force: a. when the ramp is frictionless. b. when the coefficient of kinetic friction is 0.18. Homework Equations F= ma, Ffr = μk *...
  22. M

    Why doesn't the glass move when I pull the tablecloth from under it?

    Hey guys. So I have this question about this scenario.. If I have a glass of water on a table and I quickly pull the table cloth from under the glass, the glass stays put. I can't get my head around this. What causes this?
  23. R

    Understanding Tension and Friction in Newton's Laws Homework

    Homework Statement PART A only Homework Equations The Attempt at a Solution The answer suppose to be mg sin theta- t cos alpha = 0 ( Newton's law). 15g sin36.9 = t cos 30 However, why don't we need a force of static friction?
  24. B

    Newton's Laws: Internal Degrees of Freedom

    Hello Everyone, I am currently re-reading Taylor's Classical Mechanics, in particular, section 4 in chapter 1. He is discussing Newton's Laws, and makes the statement: "A point mass, or particle, is a convenient fiction, an object with mass, but no size, that can move through space but has...
  25. R

    Newton's Laws of Motion Problem

    Homework Statement Mass of Block A = 1 kg Mass of Wedge B = 2 kg Inclination of Wedge is 37° and Cos 37° = 4/5 The wedge is given an acceleration of 5 ms-2 Find - 1. Acceleration of Block wrt Wedge 2. Normal Force Homework Equations Newton's Law for a System (hereby referred as...
  26. S

    Need help with Newton's Laws, basic Physics

    Hi, I am taking a high school physics course, and there are a few points at which I am getting a bit of confusion. My first area of confusion relates to Newton's Laws. There are a few scenarios in which I am not clear as to the interaction of forces, etc. a) Exactly why does putting...
  27. M

    Silly question about Newton's laws of motion

    I'm sorry I didn't use the outline provided automatically by the thread. My question does not focus on the maths; sorry if I chose the wrong section (I'm new here). Anyhow, what I'm asking is: Why does Newtonian Physics state that a moving object with uniform velocity (abiding by the...
  28. J

    Newton's Laws - finding acceleration of block on sled

    Homework Statement A 4.0 kg toboggan rests on a frictionless icy surface, and a 2.0 kg block rests on top of the toboggan. The coefficient of static friction μs between the block and the surface of the toboggan is 0.58, whereas the kinetic friction coefficient is 0.48. The block is pulled by...
  29. R

    Newton's Laws of Motion : Block Problem

    Homework Statement In the arrangement shown, all surfaces are frictionless, mass of block M = 30 kg and m = 20 kg. If F = 180 N , Find accelerations of both the blocks 2. Doubt What amt of force will act on larger block M, just T(coz of horizontal string around the pulley) or...
  30. J

    A small task with Newton's Laws

    Homework Statement I have been given a small task. There is two parts. (I have translated it from another language): "Santa is flying in his sleigh 836,6 feet (250 meters) above the ground. To save time, he will let the packets fall from the sack down the chimney of a house. The package is...
  31. G

    Newton's laws and submerged objects.

    I have access to a remote controlled submersible and I want to use it to do some physics with some students of mine. We are examining Newton's Laws. I intend to use spring scales to determine the mass of the sub and the max force the sub can exert by applying full forward thrust while reading a...
  32. B

    Newton's Laws Applications - Systems

    Hello, I am taking intro Physics and we are having a little quiz this friday. Professor gave us handouts and told us to solve them by ourselves, and then study those problems because the same problems will be on the quiz. Now, my problem is, is that I really don't understand the subject...
  33. V

    Newton's Laws direction and acceleration

    Homework Statement Two forces are acting on a 0.250-kg hockey puck as it slides along the ice. The first force has a magnitude of 0.405 N and points 25.0° north of east. The second force has a magnitude of 0.565 N and points 75.0° north of east. If these are the only two forces acting on the...
  34. M

    Newton's Laws: Book-Table-Earth

    Homework Statement A book is sitting on a table, which is sitting on the Earth. The book has a weight of 10 N and the table has a weight of 20 N as labeled on the diagram. a. Find all contact forces, F12. (For example, “FEB” would mean “Force of Earth ON Book”) b. Next to each, tell me...
  35. H

    What Is the Car's Acceleration Given These Forces?

    Homework Statement A 1200 kg car travels at 50 km/h and experiences air resistance of 5000 N and road friction of 2200 N. If the wheels push with a force of 7500 N, what is the car's acceleration? Homework Equations a = ƩF/m The Attempt at a Solution I got ƩF = 8590 N [E52°S]...
  36. Y

    Newton's Laws of Motion - Force Problem

    Homework Statement A 0.075-kg arrow hits the target at 21 m/s and penetrates 3.8cm before stopping. (a) What average force did the target exert on the arrow? (b) What average force did the arrow exert on the target? (c) An identical arrow strikes the target at 42m/s. If the target exerts the...
  37. B

    Question Pertaining To Newton's Laws

    Homework Statement Figure 1 shows a box of mass m2=1.0 kg on a frictionless plane inclined at angle θ=30°. It is connected by a cord of negligible mass to a box of mass m1=3.0kg on a horizontal frictionless surface. The pulley is frictionless and massless. (a) Choose the direction of your...
  38. Saitama

    Newton's laws - Pedagogical machine

    Homework Statement A "Pedagogical machine" is illustrated in the attachment. All surfaces are frictionless. What force F must be applied to ##M_1## to keep ##M_3## from rising or falling? Ans. clue. For equal masses F=3Mg Homework Equations The Attempt at a Solution I would like...
  39. C

    Elementary questions relating to Newton's laws of motion

    i) If a wall breaks when it gets hit by a cannonball, did the wall exert an equal and opposite force on the cannonball? ii) Would the force exerted by the cannonball on the wall only be the amount that was needed to break it? iii) Hypothetically, is it possible for the wall to break but...
  40. A

    Dynamics, Newton's laws, Problem with free body diagram and work

    Homework Statement A boy skateboards down a curved playground ramp. If we treat the boy and his skateboard as a particle of total mass m = 25:0 kg, he moves through a quarter-circle with radius R = 3:0 m. He starts from rest at point A and there is no friction. (a) Find his speed at the...
  41. T

    Can Newton's Laws of Motion be simplified?

    The three laws are already very simple and basic, is there any way to reduce them further?
  42. N

    Using Newton's Laws Question involving tension

    Homework Statement An old rope can now safely suspend 120 kg. When the rope is tied to a beam, it hangs down with a vertical length of 12.0 m. Calculate the minimum time required for an 85 kg person starting from rest to climb the entire length of the rope without breaking it. Homework...
  43. R

    Problem related to Newton's Laws

    Homework Statement Homework Equations ƩF=0 ƩF= m a The Attempt at a Solution Since there is no friction do I assume the objects will move? or it will remain equilibrium since m1 is 120N which is way higher than 50N.
  44. E

    Misconception of Newton's laws?

    A bird flies by pushing downwards the air below its wings with a force. According to Newton's third law, the air pushes the wings upwards. As a result, the bird is lifted. Also consider the case of a rocket. The fuel it ejects exerts an upward force and as a result, the rocket moves upwards...
  45. R

    Using Newton's Laws - A problem involving 3 masses and an incline

    This is my first time posting. I see there is a protocol for making proper posts, so I am sorry if I make any errors. Homework Statement I have a problem involving a system with an incline and three masses. A picture of the system is in the attachment labeled 15.1. I am to calculate the...
  46. M

    Finding acceleration and tension using Newton's laws

    Homework Statement http://i.imgur.com/sPN07Hi.png Homework Equations Newton's laws of motion. The Attempt at a Solution I split up the entire thing into two pieces. http://imgur.com/dMxfCZM The left diagram illustrates the left block of 3 kg. I set the x-axis parallel to...
  47. M

    Applying Newton's laws to find forces

    Homework Statement "A 1130-kg car is held in place by a light cable on a very smooth (frictionless) ramp. The cable makes an angle of 31 degrees above the surface of the ramp, and the ramp itself rises at 25 degrees above the horizontal. (a) Find the tension in the cable. (b) How hard does...
  48. A

    Are Newton's laws also an approximation?

    So are Newton's laws also an approximation to quantum phenomena. Can it be derived from quantum laws?
  49. T

    Kinematics, Newton's Laws, Fun With Engineers

    Homework Statement As a prank, your friends have kidnapped you in your sleep, and transported you out onto the ice covering a local pond. Since you're an engineer, the first thing you do when you wake up is drill a small hole in the ice and estimate the ice to be 6.7cm thick and the distance...
  50. M

    Finding Tension using Newton's Laws

    Homework Statement A picture frame hung against a wall is suspended by two wires attached to its upper corners. If the two wires make the same angle with the vertical, what must this angle be if the tension in each wire is equal to 0.75 of the weight of the frame. Ignore any friction between...
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