What is Newton's laws: Definition and 478 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. S

    Newton's Laws, Force and Kinematics

    Homework Statement A particle is traveling in a straight line at a constant speed of 24.5 m/s. Suddenly, a constant force of 14.3 N acts on it, bringing it to a stop in a distance of 52.9 m. a. Determine the time it takes for the particle to come to a stop. b. What is its mass? Homework...
  2. F

    Explaining the Relationship Between Force and Acceleration: Newton's Second Law

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  3. O

    Theory questions about Newton's Laws and Gravitation

    I'm trying to figure out these two problems and I'm so lost! 1. Two planets are circling a star. The second planet has an orbit 4 times the size of the first planet. By the time the first planet revolves once, how many times the second one will? My solution: the formula is T=2PiR/v... so...
  4. R

    Newton's laws and non inertial frame of reference

    Hi all Why do we actually say that Newton's laws do not hold for non inertial frames. can you folks give me an example of how Newton's laws collapse in an non inertial frame(if they do at all)
  5. W

    Newton's laws of motion and cars

    I kinda need help on this question because i can't find any article or references and please explain how the 3rd law related to safety devices in cars. Question: Access the design and use of injury prevention devices in cars in terms of Newton's laws of motion.
  6. N

    Newton's laws and incline surfaces

    Homework Statement A box is given an initial velocity of 5m/s up a smooth 20 incline surface . The distance the box travel before coming to rest is? Homework Equations I can't solve it correctly , I can't get the idea of this question The Attempt at a Solution x= ? vi=5 v=0...
  7. F

    Speed bump question - Newton's laws

    1. You're driving down the road at 8 m/s and go over a speed bump. When you go over the bump, you feel lifted from your seat. Explain why. I assumed it was because of inertia, but I'm not sure. You weigh 700 N. If it is approximated that the speed bump is shaped like an arc of a circle...
  8. F

    Two conceptual questions regarding Newton's laws

    1. Why is it that when you swing a ball around your head, the string or rope attached to the ball is always tilted down a little? That is, the rope isn't parallel to the floor, it is at a bit of angle at down. 2. The ball will continue to move in a circular path if the total force is...
  9. M

    Newton's Laws Practice Problem: Finding Force on Book During Braking

    Homework Statement Your 3.10 kg physics book is next to you on the horizontal seat of your car. The coefficient of static friction between the book and the seat is 0.640, and the coefficient of kinetic friction is 0.540. Suppose you are traveling at 79.2 km/h = 22.0 m/s and brake at a constant...
  10. A

    How Do Newton's Laws Apply to a Block and Toboggan on a Frictionless Surface?

    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 between the block and the surface of the toboggan is 0.60, whereas the kinetic friction coefficient is 0.51. The block is pulled by...
  11. P

    Newton's Laws of Motion on a rocket

    Suppose the rocket is coming in for a vertical landing at the surface of the earth. The captain adjusts the engine thrust so that rocket slows down at the rate of 2.50m/s^2 . A 8.00-kg instrument is hanging by a vertical wire inside a space ship. 1]Draw a free-body diagram for the instrument...
  12. P

    Understanding Motion in a Pulley System

    Homework Statement A smooth ring A of mass m can slide on a fixed horizontal rod. A string tied to the ring passes over a fixed pulley B and carries a block C of Mass M (=2m) as shown in the given figure. At a instant at the string between the ring and the pulley makes an angle \theta with...
  13. D

    Forces and Newton's Laws with vectors help

    Homework Statement One force of 60N and a second of 30N act on an object at point P. Graphically add the vectors and find the magnitude of the resultant when the angle between them is as follows. a. 0 b. 30 c. 45 d. 60 e. 90 f. 180 Homework Equations A-Sin A = B/Sin B...
  14. R

    Applying Newton's Laws (Inertia, F=ma, Action Reaction_

    Hey guys, This is my first time using these forums, so forgive me if I do/post anything wrong! Anyways, I need help on a question...and this might be on a physics test I'm having tommorow. I'm not that great in physics, so I need a bit of help. If anyone can tell me their opinion, please do so...
  15. N

    Conservation of energy derived from Newton's Laws?

    Homework Statement "Show how conservation of energy (with only gravitational potential energy and kinetic energy) can be gotten from Newton's Laws. This was the question that was asked of me, and sorry for the wording not being terribly precise. Homework Equations I am not exactly...
  16. C

    How Do Newton's Laws Apply to a System of Hanging Masses?

    Homework Statement Three ballot boxes are connected by cords, one of which wraps over a pulley having negligible friction on its axle and negligible mass. The masses are mA = 32.0 kg, mB = 40.0 kg, mC = 18.0 kg. (box a is on the horizontal suface and b and c hang down. (a) When the...
  17. mbisCool

    What Determines the Monkey's Acceleration When It Stops Climbing?

    Homework Statement A 8 kg monkey climbs up a massless rope that runs over a frictionless tree limb and back down to a 15 kg package on the ground. Assume that after the package has been lifted, the monkey stops its climb and holds onto the rope. (b) What is the monkey's acceleration...
  18. N

    How Do Newton's Laws Apply to These Real-World Physics Problems?

    Homework Statement 1. A man stands on a scale in an elevator that has an upward acceleration a. The scale reads 960 N. When he picks up a 20kg bos, the scale reads 1200 N. Find the mass of the man, his weight, and the acceleration a. 2. A horizontal force of 100 N pushes a 12kg block up a...
  19. H

    Newton's laws / pulleys question?

    I have uploaded the problem here: http://i36.tinypic.com/mps9i.jpg These are the answers I have gotten so far: a) L1 = 2*P1 - P2 - x1 + (pi*R) L2 = 2*P2 + (pi*R) - x2 b) Forces on M1 --> M1*g downward, and T1 upward, which I think is equal to M2*g. Therefore a1 = [(M2 - M1)*g] / M1...
  20. M

    Newton's Laws Problem- Question on upcoming TEST

    Newton's Laws Problem- Question on upcoming TEST! Homework Statement A small block is placed at height h on a frictionless 30 degree ramp. Upon being released, the block slides down the ramp then falls 1.0 m to the floor. A small hole is located 1.0 m from the end of the ramp. From what...
  21. H

    How Do I Calculate the Gravity on Saturn with its Given Radius and Mass?

    I have got this word problem and I tried to solve but could not find the exact answer and I need the way to do it because my upcoming test has similar problems to it,, Homework Statement Saturnn has an equatorial radius of 6.00 * 107m and a mass of 5.67 * 1026Kg. Calculate the following...
  22. T

    Newton's Laws: Sharp vs. Dull Knives

    Homework Statement Why does a sharp knife cut better than a dull knife? Explain using Newton's Laws. The Attempt at a Solution 1st Law: Since the sharper knife has less surface area, it keeps more better than the dull knife. The friction is less. 2nd Law: Less surface area on knife...
  23. M

    What Is the Acceleration of a Towed Glider?

    Homework Statement An airplane of mass 1.2 x 10^4 kg tows a glider of mass 0.6 x 10^4 kg. The airplane propellers provide a net forward thrust of 3.6 x 10^4. What is the gliders acceleration. Homework Equations F(net) = ma The Attempt at a Solution After drawing FBD's...
  24. D

    Breaking the Sound Barrier: Calculating Time and Thrust of a Rocket Launch

    A 25,000-kg rocket blasts off vertically from the Earth's surface with a constant acceleration. During the motion considered in the problem, assume that g remains constant. Inside the rocket, a 15.0-N instrument hangs from a wire that can support a maximum tension of 35.0 N. a) Find the...
  25. C

    How Do Newton's Laws Apply to a Pulley System with Unequal Masses?

    Homework Statement http://img213.imageshack.us/img213/6969/physicsproblemhq3.png A rope of negligible mass passes over a pulley of negligible mass attached to the ceiling as shown above. One end of the rope is held by Student A of mass 70 kg, who is at rest on the floor. The opposite end...
  26. D

    What are the equations and steps to solve these two problems?

    I have two separate problems that I think require essentially the same equations and thought process. So if I can get one I should be able to get the other: First problem Homework Statement A bat crashes into the vertical front of an accelerating subway train. If the coefficient of...
  27. C

    Newton's Laws, blocks of mass and string

    Homework Statement Two small blocks each of mass m, are connected by a string of constant length 4h and negligible mass. Block A is placed on a smooth tabletop and block B hangs over the edge of the table. The tabletop is a distance 2h above the floor. Block B is a distance h above the...
  28. O

    Mechanics Problem Involving Newton's Laws

    Homework Statement An arrow, starting from rest, leaves the bow with a speed of 19.5 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 f=ma The Attempt at a...
  29. P

    Applications of Newton's Laws of Motion

    1. A toboggan slides down a hill and has a constant velocity. The angle of the hill is 8.00 with respect to the horizontal. What is the coefficient of kinetic friction between the surface of the hill and the toboggan 2. Static Frictional Force, FsMax=msFn 3. I have no freaking...
  30. L

    Forces and Newton's Laws of tension

    A 204-kg log is pulled up a ramp by means of a rope that is parallel to the surface of the ramp. The ramp is inclined at 29.6 ° with respect to the horizontal. The coefficient of kinetic friction between the log and the ramp is 0.825, and the log has an acceleration of 0.734 m/s2. Find the...
  31. M

    Newton's Laws: Force of Tension

    Homework Statement A mountain climber, in the process of crossing between two cliffs by a rope, pauses to rest. She weighs 600 N. As the drawing shows, she is closer to the left cliff than to the right cliff, with the result that the tensions in the left and right sides of the rope are not the...
  32. T

    Solving Problems with Newton's Laws - Hanging Chandelier

    Homework Statement A chandelier with mass m is attached to the ceiling of a large concert hall by two cables. Because the ceiling is covered with intricate architectural decorations (not indicated in the figure, which uses a humbler depiction), the workers who hung the chandelier couldn't...
  33. C

    Exploring Newton's Laws of Motion

    I curious about Newton have how many laws?
  34. D

    Understanding Newton's Third Law of Motion: A Law of Forces Explained

    It is clear that Newton's first two laws of motion deal with motion: the velocity of a moving body is persistant, and net forces cause acceleration of such a body. However, in my opinion, the third law has more to do with the nature of forces rather than motion. The main point is that forces...
  35. R

    Motion at a Constant Acceleration - Newton's Laws

    Suppose you want to design an air bag system that can portect the driver in an head-on collision at a speed of 100 km/h. Estimate how fast the airbag must inflate to protect the driver. The answer to this question would be-- t= 0-28/ -390 = 0.07 seconds using the law X= Xo + Vo t + 1/2...
  36. J

    How Does Newton's Laws Apply to a Piano on an Incline?

    Homework Statement A man pushes on a piano with mass 180 kg so that it slides at constant velocity down a ramp that is inclined at 11deg above the horizontal floor. Neglect any friction acting on the piano. Calculate the magnitude of the force applied by the man if he pushes (a) parallel to...
  37. J

    Relativity: position/acceleration 4-vectors to Newton's laws

    Homework Statement Given the binomial expansions for sinh and cosh, so that the acceleration and position 4-vectors reduce to x=1/2 a t^2 for small t. Homework Equations Okay, so we have cosh (x) = 1 + x^2/2 + ... and sinh(x) = x + x^3/3 ... We have the...
  38. A

    What does the scale read when two 100N weights are attached to a spring scale?

    Homework Statement http://img131.imageshack.us/img131/2996/physicswb9.th.png Two 100N weights are attached to a spring scale as shown. What does the scale read? Homework Equations The Attempt at a Solution This concept is difficult for me to grasp. My natural instinct...
  39. G

    A couple of question regarding tension and Newton's laws

    1. A led cylinder hangs on a string. By another string, another cylinder is hung on the previous cylinder. If you pull fast enough, the lower string tears, if you pull slowly, the upper one tears. How does one explain this? I tried to explain this with the help of Newton's second law, but I...
  40. A

    Solving Newton's Laws: Get Help Here!

    Homework Statement In the attach Homework Equations Newton Laws The Attempt at a Solution Ok, I did the first one, came up with T2 = 8.736, is that right? What is the net force? How do I do the third one? 10x in advance.
  41. D

    How Do Newton's Laws of Motion Apply to Everyday Life?

    hello can some one help me, post a simplified version of Newton's 3 laws of motion and some examples thank you very much :)
  42. C

    A few questions regarding Newton's Laws

    Okay, I have a few questions. Feel free to answer any that you can. (Even if it's only one.) :-p 1. What is an inertial reference frame? (Provide examples please.) 2. The mass of an object is a quantitative measure of inertia. What does this mean? 3. Is a net force being applied to an...
  43. S

    Physics teacher needs help with lab on Newton's laws

    Hello! I am a high school teacher and I am doing a lab on Newton's laws. I need help interpreting part of the lab because the results did not come out to what the laws would have predicted. The lab consisted of setting up two carts, one with a spring which can be compressed and one...
  44. R

    Circular Motion with Newton's Laws

    A model airplane of mass 7.50 with a speed 35m/s flies in a horizontal circle at the end of 60.0m control wire. Aerodynamic lift acts on the plane at an angle of 20 degrees West of North. In the picture the book has the plane on the right. The weight is acting straight down, the tension is...
  45. R

    Circular Motion and Newton's Laws

    A model airplane of mass 7.50 with a speed 35m/s flies in a horizontal circle at the end of 60.0m control wire. Aerodynamic lift acts on the plane at an angle of 20 degrees West of North. In the picture the book has the plane on the right. The weight is acting straight down, the tension is...
  46. D

    Newton's laws and working with systems

    Homework Statement Say you have three carts connected by strings, with each cart's mass being 50kg, which way would the tension for be pointed in a free body diagram? By the way, the carts are accelerating.. []-[]-[] accelerating --> @ 3m/s/s
  47. T

    Newton's Laws of Motion on an airplane

    Homework Statement Your airplane is caught in a brief, violent downdraft. To your amazement, the pretzels on your seatback tray rise vertivally, and you estimate their upward acceleration relative to the plane at 2 m/s^2. What's the donward acceleration of the plane? ANy suggestions are...
  48. R

    Revisiting Newton's Third Law: Understanding Momentum and Additivity

    Now a part of a project or anything, but a product of a question a friend of mine asked about the third law. Please correct any mistakes, and tell me what you think of this write-up I wrote. http://anonicker.googlepages.com/Newton%27slaws"
  49. I

    Applying Newton's laws to traveling car

    [b]1. A car traveling at 62 km/h hits a bridge abutment. A passenger in the car moves forward a distance of 57 cm (with respect to the road) while being brought to rest by an inflated air bag. What magnitude of force (assumed constant) acts on the passenger's upper torso, which has a mass of 46...
  50. N

    What is the Optimal Distance for a Frictionless Track to Minimize Time?

    Homework Statement A frictionless track is to be built as shown, with L=4.60m and H=4.80m. In order to get the cart to slide from the top to the end of the track in the minimum time, how long should the distance D be? Assume that the speed of the cart on the horizontal surface is the same as...
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