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. C

    Newton's laws - studying for a test

    Hello guys. I have a test in a couple of days, so I am hoping to get some practice. I'll post any questions I have here, I would appreciate if you guys can help me clear up any confusions. 1. A 400-N block is dragged along a horizontal surface by an applied force F as shown. The coefficient of...
  2. S

    Help with Newton's Laws (AP Physics B)

    Homework Statement they keep telling me it is a simple problem, I've actually done harder problems of the same thing, but i just don't seem to get this one. A 15kg block sits on a 25kg block. The coefficient of static friction between the blocks is 0.408 and there is no friction between...
  3. T

    Kepler's 3rd Law as a result of Newton's Laws

    thanks in advance for any and all help! The question is to show that Kepler's 3rd Law holds when you assume circular orbit with TWO gravitating bodies both orbiting around the center of mass. (by equating gravitational and centripetal forces and finding the constant of proportionality which...
  4. C

    Force and Newton's Laws of Motion

    I came across this question, " An 8000 kg engine pulls a train of 5 wagons, each of 2000 kg along a horizontal track. If the engine exerts a force of 40000 N and the track offers a frictions of 5000 N, then calculate the force exerted by wagon 1 on wagon 2." In this question,if we consider...
  5. F

    Newton's laws problem: K&K 2.19

    Homework Statement A pedagogical machine is illustrated in the sketch, yatta yatta, what force F must be applied to M_1 to keep M_3 from rising or falling? No friction. Here's the http://www.slideshare.net/brigittperalta/sol-maquina-pedagogica-1546585" . The Attempt at a Solution If we...
  6. J

    Newton's Laws, bungee jump problem

    Please help me with this problem. many thanks :) A 55-kg bungee jumper has fallen far enough that her bungee cord is beginning to stretch and resist her downward motion. Find the force (magnitude and direction) exerted on her by the bungee cord at an instant when her downward acceleration has a...
  7. J

    Help, please on vectors and Newton's laws

    Hello :) This is my question: A 325-kg boat is sailing 15 degrees north of east at a speed of 2 m/s. Thirty seconds later, it is sailing 35 degrees north of east at a speed of 4 m/s. During this time, three forces act on the boat: a 31 N force directed 15 degrees north of east (due to an...
  8. N

    Question Related to Newton's Laws of Motion

    1. A fully loaded Saturn V rocket has a mass of 2.92 x 10^6 kg. Its engines have a thrust of 3.34 x 10^7 N. a. What is the downward force of gravity on the rocket at blast-off? b. What is the unbalanced force on the rocket at blast-off? c. What is the acceleration of the rocket as it...
  9. T

    Newton's Laws question : On springs and pulley system

    A Particle is attached by a string to a point in a rough inclined plane of elevation \theta. Co-efficient of friction is \mu. Originally, the string is unstretched and lay along the line of greatest slope.Prove that the condition for particle to oscillate is \mu < 1/3tan\theta. Note : Tension...
  10. M

    Calculating Block's Backward Pull in Physics Problem?

    Hey, I have a question I'm stuck on for my grade 12 physics class. There is a block being pulled by tension over a triangle essentially that's at a degree of 35.7 (right angle triangle). I understand the whole question but I don't understand how to find how much pull the block has backwards of...
  11. W

    What will happen to the crate of eggs when a truck makes a sharp left turn?

    A truck driver is carrying a crate of eggs to a local gorcery store. When the driver gets off the highway, he makes a sharp left turn. According to Newton's Laes, what will happen to the crate of eggs? a. The crate will slide to the right in the truck. b. The crate will slide to the left in...
  12. F

    Questions on dynamics - Newton's laws of motion

    1. A chain of mass M and length L is suspended vertically with its lower end touching a scale. The chain is released and falls onto the scale. What is the reading of the scale when a length of the chain x has fallen? You may neglect the size of the individual links. 2. A smooth wedge, whose...
  13. V

    Solving the Elevator's Acceleration: Examining Newton's Laws

    Homework Statement An object is placed on a scale in an elevator which reads 8kg at rest. This scale shows 9.2kg when the elevator accelerates. What is the direction and magnitude of the elevator's acceleration. Homework Equations F=MA, F=MG, Fnormal=m(a-g) The Attempt at a Solution...
  14. M

    Conceptual question: Newton's Laws

    Suppose you have a can (like a spray can) in a vacuum. You poke a hole in the can and the pressure from the can pushes it to the right. Now suppose you have a vacuumed can within a pressurized container and then you poke a hole in it. Which way (if at all) does it move? I know this is sort of...
  15. A

    Newton's Third Law and Tractor Movement

    Homework Statement A tractor is pulling a heavy weight behind it by a rope. If, according to Newton's third law, the load is pulling back as hard as the tractor is pulling forward, then why does the tractor move? Something else I don't really get: A fishline will break when a force of more...
  16. A

    Relating Homework problems to Newton's laws

    Hi guys, I realize this can be a rather uncanny occurance when a new member's first post is to ask for physics help on his homework but I've been lurking around the forum here for a while and am now in a really tight spot and thus had to get over myself and finally make an account...
  17. P

    Is This Scenario Demonstrating Newton's Third Law of Motion?

    Let's say there's two people, A and B. Person A hits person B and person A gets pushed back more than person B does. Would be that be exhibiting Newton's Third Law of Motion of Newton's Second Law of Motion?
  18. J

    Newton's laws, finding acceleration and force

    Homework Statement A large football player student (1.0 x 10^2 kg) applies a 6.0 x 10^2 N force to another equally burly student (1.0 x 10^2 kg) sitting on a sled (13.2 kg). If sliding friction and air resistance (drag) is 99.5 N, find the acceleration of the sled. In addition, how much...
  19. M

    Need extra practice for Newton's laws?

    Does anyone have a good website for some questions/answers for Newton's three laws (I'm not sure if he made more, but the inertia, the net force must be zero when something is not moving, or moving at a constand rate, and the for every action there's a reaction). I've got a test tommorow, and I...
  20. S

    How Do Newton's Laws Apply to Everyday Motion and Animal Adaptations?

    Homework Statement Sorry to bother, but I was working through some homework I haven't done (I put a * next to ones I didn't get and I just wanted to post them because I have no idea how to do them): 1. If you are on a bus that is traveling along a straight, level road at 100 km/h, you are...
  21. I

    What Force Allows a Balloon to Float in the Air?

    As the balloon rises, the force of gravity pulls on the balloon, but which force is strong enough to pull the balloon up so that it floats in the air? thanks
  22. ThomasMagnus

    How can the window washer move at constant velocity with unbalanced forces?

    A window washer pulls himself upward using the bucket pulley apparatus shown. How hard must he pull downward to raise himself at a constant speed? The mass of the person and the bucket is 65kg. My attempt: When doing pulley problems, I like to set 'moving to the right' as positive. In this...
  23. J

    How Do You Calculate the Coefficient of Kinetic Friction on an Inclined Slide?

    Homework Statement A child slides down a slide with a 34 degree incline, and at the bottom her speed is precisely half what it would have been if the slide had been frictionless. Calculate the coefficient of kinetic friction between the slide and the child. Homework Equations \SigmaF...
  24. B

    Newton's Laws Question: Skateboard Speeds After Release | F=ma Explained

    Jack and Jill are on skateboards. Jack weighs 3 times heavier than Jill, and is pushing Jill(a horizontal force on Jill's back). Immediately after Jack let's go, what are the speeds they're moving at? (No need to take friction into consideration) F=ma Okay, I do understand that they will be...
  25. E

    How Do You Calculate Force and Distance in Physics Problems?

    Homework Statement 1.On an aircraft carrier, an F18 Super Hornet can be catapulted from 0 to a take-off speed of 248 km/hr. The loaded mass of this jet in fighter configuration is 21,320 kg. The length of the angled section of the flight deck on the US Nimitz class carriers is 237 m. What...
  26. A

    Analyzing the Motion of a Thrown Box Using Newton's Laws of Motion

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  27. A

    Applying Newton's Laws and solving multiple object system question

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  28. M

    Newton's laws of motion discussion question

    this is from chapter 4 of university physics of young and freedman q19 why can it hurt your foot more to kick a big rock than a small pebble? must the big rock hurt more? explain? but I can't see the answer at all by just applying Newtons law in the scenario of the small pebble mp is small...
  29. F

    Newton's Laws, not sure which law this is, also FBD

    Homework Statement http://img576.imageshack.us/img576/5773/67450733.jpg Suppose three blocks as stacked as shown on a floor which I forgot to draw and assume it is frictionless. Draw a free-body diagram for each mass Now I know my FBD is wrong because it is a misconception of Newton's third...
  30. N

    Dot product, cross product, Newton's laws.

    My final for Physics is coming up and I really, really ****ed up in this class. I don't even know how to do dot products, cross products, or let alone Newton's laws. We applied Newton's laws to some pulley problems I think. I've been going to all the lectures but it just doesn't stick -- nothing...
  31. L

    How long does it take to move a box of books across the floor?

    Homework Statement A box of books weighing 329 N is shoved across the floor by a force of 484 N exerted downward at an angle of 32◦ below the hori- zontal. The acceleration of gravity is 9.81 m/s2 . If μk between the box and the floor is 0.57, how long does it take to move the box 3.66 m...
  32. M

    Newton's Laws, Kinematics, and Friction

    Homework Statement A student pushes horizontally northward on a 1.5 KG textbook initially at rest. The book is located 1.0m from the edge of a long table. the coefficient of static friction is 0.25, and the coefficient of kinect friction is 0.20. The applied force is just enough to get the...
  33. P

    The jumping skier (momentum, Newton's laws, energy)

    Homework Statement So, there is a skier (the blue recktangle) preparing to do a jump. There is no friction between the skier and the jumping board, and also no friction between the jumping board and the ground. Known values are: v0 - starting speed of the skier m2 - mas of the...
  34. P

    Newton's Laws and finding magnitude

    An object of mass 1.25 kg on a flat surface has two forces acting on it, F1 and F2 in the horizantal direction. F1 acts in the positive direction, F2 acts in the negative direction. The magnitude of F1 is 26.75 N. The object moves strictly along the horizontal x-axis, which we choose as positive...
  35. A

    Newton's Laws grade 11 physics

    Homework Statement A toboggan with a mass of 15kg is being pulled with an applied force of 45 N at an angle of 40degrees to the horizontal. What is the acclecration if the force of friction opposing the motion is 28 N?Homework Equations Is this question related to the x and y component rules...
  36. P

    Newton's Laws and finding acceleration

    Homework Statement A brick of mass 1.0 kg slides down an ice roof inclined at 30 degrees with respect to the horizantal. If the brick starts from rest, how fast is it moving when it reaches the edge of the roof 0.90s later? Ignore friction Homework Equations Fnet = ma v2 = v1 +...
  37. P

    Frictional Forces and Acceleration: Solving for Horizontal Component

    Homework Statement Two blocks are accelerated across a horizontal frictionless surface as shown. Frictional forces keep the two blocks from sliding relative to each other, and the two move with the same acceleration. F = 1.2 N and M = 1.0 kg Homework Equations what is the horizontal...
  38. T

    Passive forces and Newton's laws

    A block can move with constant velocity even though it has an applied force. Newton's first law is NOT violated. We were going over this in class today but I don't understand it, why is Newton's first law not violated? What applied force would you need to keep the block moving with a...
  39. S

    Newton's Laws of motion problem

    Homework Statement A block weighing 70.0 N rests on a plane inclined at 25.0° to the horizontal. A force F is applied to the object at 35.0° to the horizontal, pushing it upward on the plane. The coefficients of static and kinetic friction between the block and the plane are, respectively...
  40. J

    Newton's Laws Questions + Friction. Very tricky and help appreciated

    I AM NOT INTERESTED IN DIRECT ANSWERS! I'm just stuck on how to process these questions and just need a little guidance on what I'm doing wrong. I will be forever indebted and I am more interested in learning how to solve for these. Thank you! 1. A person weighing 0.9 kN rides in an...
  41. J

    How do I find the necessary force to start a crate moving on a rough floor?

    Homework Statement To move a large crate across a rough floor, you push on it with a force F at an angle of theta=21.0 degrees below the horizontal. Find the force necessary to start the crate moving, given that the mass of the crate is 32.0 kg and the coefficient of static friction between...
  42. E

    What is the explanation behind Newton's Laws?

    Homework Statement I need someone to help me fully understand Newton's Laws. I kinda get his second law, the sum of the forces equals mass times acceleration??, but yea. Homework Equations Newton's First Law Newton's Second Law...
  43. J

    Finding Acceleration in a Frictionless System with Multiple Masses

    Homework Statement What is the acceleration of the masses as shown in the second attached image. m1 = 0.9kg, m2 = 1.6kg, and m3 = 2.4kg. (Assume the table is frictionless) Homework Equations \sumF=ma F_mg+FN = ma The Attempt at a Solution I figured everything up to the point...
  44. J

    What is the mass of the hanging block in this system in equilibrium?

    Homework Statement T here are 2 blocks connected by a string, as shown in the first image attached. The smooth inclined surface makes an angle of 40 degrees with the horizontal, and the block on the incline has a mass m1 = 7.9kg. What is the mass of the hanging block m2 that will cause the...
  45. C

    Newton's laws in variable mass systems

    Thread split from this thread. Not true. The spray can is generating a constant force, not a constant power. As a result, the work done by the spray can depends on the distance it travels, and the power generated depends on the rate at which it is traveling. The farther the spray can travels...
  46. O

    Newton's Laws of Motion problem help

    Hi everyone! I am really bad in physics so I need help in my assignments. My problem is what formula to use. Here's the problems. Homework Statement An electron (mass = 9.11 x 10-31 kg) leaves one end of a tv picture tube with zero (0) initial speed and travels in a straight line to the...
  47. R

    Newton's Laws with Friction; Inclines

    Homework Statement A car can decelerate at -4.80m/s^2 without skidding when coming to rest on a level road. What would its deceleration be if the road were inclined at 13degrees uphill? Assume the same static friction coefficient. Homework Equations Ffr=µkFN The Attempt at a...
  48. M

    Proving rotational motion using Newton's laws

    I have asked this question before, but couldn't get a satisfactory response. Let me make the problem more concise. We have a two particle system, i.e. two masses of mass m each joined together by a spring of spring constant k. A force F is applied to one of these particles in a direction...
  49. M

    Deriving the equations of torque and ang. Momentum from Newton's laws

    I know what the definition of torque and angular momentum is. But I read in a few books that "Torque and angular momentum are not independent laws of nature, and have been derived from the more fundamental laws of Newton." The above simply means, that the rotational motion is just a...
  50. ThomasMagnus

    How can Newton's Laws be applied to the motion of a bus and a person on it?

    Hi there, I have two simple physics questions. One day I was on the bus, and began to wonder why I kept getting thrown to the back every time the bus accelerated. Which one of Newton's laws can be applied to this?-if any. Another question is: When a rocket takes off, it applies a force in...
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