Newton 2nd law Definition and 142 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. Q

    I Bike going downhill brakes front wheel

    I'm an avid bike rider and a first year physics student. A couple days ago a friend of mine told me about how his friend was going downhill on her bike, used her front brake, and went over. I would like to determine what the minimum speed for a given slope angle is for the biker to do a full...
  2. MickeyBlue

    Tension in two wires at unknown angles

    Homework Statement An object at rest is suspended from two strings (A and B) as shown in the diagram, with A shorter than B. The object pulls on the point O with a force of 20 N. Each of the strings also exerts a force on the Point O. The angle between the strings at O is 90o. Which of the...
  3. G

    I What Is Four-Force in Special Relativity?

    Hi. One of my undergrad professors emphasized explicitly that Newton's second law $$\mathbf{F}=\frac{d\mathbf{p}}{dt}$$ is not a definition of force, but an empirically found relation between a force law (e.g. Hooke's law) and the change of momentum of an object this force acts upon. Wikipedia...
  4. Zack K

    Applied force of a ball on a glove

    Homework Statement A 0.145 kg baseball traveling at 35.0 m/s strikes a catcher's mitt which, in bringing the ball to rest, recoils backwards 0.11 m. What was the average force applied by the ball on the glove Homework Equations Fnet=ma or F=ma The Attempt at a Solution I am honestly so lost...
  5. Sqrt

    Understanding Momentum & Force: Self-Studying Physics Tips

    Hey, Just started studying this chapter and everything is just floating around my head. I am self studying Newton's Laws of motion and I'm having trouble imagining and getting used to it. Like i can't get a feel of force or momentum. I hope you get what I mean even though it sounds wired...
  6. J

    I Spacecraft Launches: Perigee & Apogee - Why Terminate?

    why spacecraft launches are usually terminated at either perigee or apogee?
  7. J

    An application of free fall (DE) model to industry

    Could someone tell me an application of the model of free fall to industry or more generally by using Newton's second law and the law of gravitation, construct a model similar to the free fall one, that has an application in industry
  8. J

    Additivity of mass: provable from Newton's laws?

    Within the context of Newton's laws, it seems implicitly understood that mass is an additive property of objects. My question is: should this be considered "just" an experimentally confirmed fact, or is is provable from Newton's laws? The following is a more precise context for this question...
  9. Holden Kenne

    B Understanding Newton's Laws of Motion: Exploring Errors and Contradictions

    Hi, I'm a frehshman in High school writing a paper about Isaac Newton. One of my paragraphs is about the laws of motion. I came across a tidbit of information - there are instances in which Newton's laws are not correct. One example I found was that, at speeds approaching that of light, an...
  10. P

    Two blocks on a frictionless surface; find the force

    Homework Statement Two blocks, A and B , are being pushed on a frictionless surface by a froce of 30 N to the right, .Block A has a mass of 2.0kg, Block B, being pushed by Block A is 4.0kg. Calculate the magnitude of the force that block B exerts on Block A. Homework Equations f=ma The...
  11. L

    Path of a Particle: Find & Solve Questions

    Homework Statement Homework Equations Find the path of a particle. What is the general or fundamental way to solve this type of questions ? The Attempt at a Solution I don't know where do i start. I can't able to find a relation between these vectors.
  12. L

    B Finding the Path of a Particle with Initial Velocity and Force

    Hi There. I want to ask a question, here it is :- How to find the path of a particle if initial velocity(vector) is given and constant force(vector) acts on the particle. Like :- 1) How can we determine the path will be PARABOLIC 2) How can we determine the path will be CIRCULAR. 3) How can we...
  13. A

    Holding a block of mass in equilibrium on a slope

    Homework Statement A block of mass is held in equilibrium on an incline of angle 30 degrees by the horizontal force 500N. Determine the blocks's weight, ignore friction. Homework Equations F = MA Normal Force y = Fg*sin(theta) Normal Force x = Fg*cos(theta) The Attempt at a Solution I'm...
  14. M

    Calculate the average resultant force required to accelerate the ball.

    Homework Statement A 56 g tennis ball is accelerated at 1000 m s-2 to reach its service velocity. Calculate the average resultant force required to accelerate the ball. Homework Equations F = MA The Attempt at a Solution Mass = 0.56g = 0.056kg Acceleration = 1000m/s2 0.056 x 1000 = 56N...
  15. Anjum S Khan

    Is the Force Applied to the Ball Zero in this Scenario?

    Homework Statement I am pushing a very heavy ball with full strength, but the ball is not moving at all. So, there is no change in momentum of the ball. Is it appropriate to say that the Force applied to the ball is zero ? Homework EquationsThe Attempt at a Solution
  16. Anjum S Khan

    A body thrown upwards with some external force

    Homework Statement A ball of mass of 1Kg is held in hand. The moment it is released from hand, without any delay it is hit by an external force of 100N in upwards direction. How high will the body go ? Homework EquationsThe Attempt at a Solution I know how to solve if instead of Force we...
  17. Alexiy

    Find the differential equation and velocity

    Homework Statement Homework Equations 3. The Attempt at a Solution [/B] Hello guys,I posted images since its easier to write equations.Please can someone help me check this, if this is correct so far, then i should be able to find the velocity at C, using kinetic energy?
  18. C

    Confusion about type and quantity of force being exerted

    Homework Statement A 500-N person stands 2.5 m from a wall against which a horizontal beam is attached. The beam is 6 m long and weighs 200 N (see diagram below). A cable attached to the free end of the beam makes an angle of 45 degrees to the horizontal and is attached to the wall. a) draw a...
  19. REVIANNA

    Classical mechanics: forces on a pendulum

    Homework Statement [/B] A simple pendulum is pulled sideways from the equilibrium position and then released. I figured this part out - Immediately after the pendulum is released, the net force acting on it is directed: it is perpendicular to the string (I REASONED THAT THE DIRECTION OF...
  20. Tibriel

    A person and a box of equal mass are on a pulley with v=0....

    Homework Statement person and a box of equal masses are hanging off of the same pulley. The rope is considered massless. The person and the box are separate from each other. (The person is NOT standing on the box.) Homework Equations How far does the box move if the person starts climbing...
  21. G

    What is the Exact Meaning of F=dp/dt?

    Hi. Force was introduced to me as "what a force meter in an inertial frame measures". I'm a bit confused about the interpretation of Newton's second law$$F=\frac{dp}{dt}\enspace.$$ Is it a definition? Is it an empirical finding? Can it be derived theoretically? Or do we need to make the...
  22. J

    Effect of wind speed on running

    Hi guys, I'm an arts undergrad student with very little knowledge of the sort of physics I'm about to ask. I was wondering if there is a calculation to work out the differentiation between running at a particular speed say 10mph against wind coming towards you at 15mph. As well as it being on...
  23. N

    Clarification of the laws applied

    I am a first year student and i am required to build one thing based on one physics law . if i build a rubber band powered airplane , what laws should i say it applies? and what about rubber band powered car??
  24. K

    Half atwood machine with accelerating pulley

    Homework Statement [/B] Consider a half-atwood machine on a cart as below, with mass m_2 attached to M via a frictionless track that keeps it pinned to M but allows it to move vertically. All surfaces (except between the wheels/ground) are frictionless, and the pulley and rope are massless. If...
  25. O

    Task: Function for the acceleration throughout a loop?

    So, this seemed really fun to me until I got stuck. THE TASK is about an object with mass m, moving in a basic (2D) coordinate system. It is attached to origo (0, 0) by a "rope" with constant length r=5. In position P0(-5, 0) it has the velocity v0=[0, -10]. Hence, the object moves around origo...
  26. D

    Finding Tension of a string tied to a wall

    In the figure we see two blocks connected by a string and tied to a wall, with θ = 33°. The mass of the lower block is m = 0.9 kg; the mass of the upper block is 4.0 kg. Find the tension in the string that is tied to the wall. -I have the forces of Block A as Tension, Normal Force, and Gravity...
  27. manaXmizery

    Forces acting on two stacked blocks

    Homework Statement A 1.5 kg block rests on top of a 7.5 kg block which are attached using a cord to a pulley - there is no friction anywhere. What force must be applied to the bottom block so the top block accelerates to the right at 2.5 m/s^2? Homework Equations m1 = 1.5kg a(to the right) =...
  28. Samei

    Force of Falling Objects at a Height

    Homework Statement : [/B]I'm curious to know why and how one would account for the force of a falling object dropped from a height. If I apply Newton's 2nd Law, force is only dependent on acceleration. So in a straight vertical drop, this acceleration is only gravity. But is it not that a...
  29. tjvv

    Conversion of g acceleration into "body weight"

    Hi guys, I have a table with vertical peak acceleration values [g] and I want to find out a formula that convert the [g] values into ground reaction forces in units of body weight (BW). I think Newton´s 2nd law (F = m x a) may help but I am stuck on finding a generic relationship (problem is...
  30. K

    Box Pushed Up an Incline Ramp: Basic Newton's Law Questions

    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. when the ramp is frictionless. when the coefficient of kinetic friction is 0.18 Homework Equations F=mg FN=mg μ= Fk/FN The...
  31. R

    Tension on a Rope Deflected by a Pulley: Differentials

    Hi all, first post here. I'm a junior Physics/Math double major at UMass Amherst, playing with some problems over the summer. I'll get right into it. A rope with constant tension T is deflected through the angle 2\theta_{0} by a smooth, fixed pulley. What is the force on the pulley? It is...
  32. SpacemanRich

    Newton's second with Pullys, Ropes, and Boxes (Frictionless)

    Homework Statement [/B]In the drawing, the rope and the pulleys are massless, and there is no friction. Find (a) the tension in the rope and (b) the acceleration of the 10.0-kg block. (Hint: The larger mass moves twice as far as the smaller mass.) 2. Formula's Used. F = ma, W = Mg. The...
  33. SpacemanRich

    Newtons' Second Law with Kinetic Friction Problem

    Homework Statement While moving in, a new homeowner is pushing a box across the floor at a constant velocity. The coefficient of kinetic friction between the box and the floor is 0.41. The pushing force is directed downward and an angle θ below the horizontal. When θ is greater than a...
  34. 1

    Why is there a vertical force on the pin in this static equilibrium setup?

    Q: Why does the pin have a vertical force in this diagram (Static equilibrium)? The diagram depicts as follows: A mass (M) sits a a distance (d) away from the end of a board of length L. The board has a mass of m and is held to a wall by a pin and string. The string has a tension (T) and is at...
  35. P

    Newton 2nd. 2D velocity fn. Distance (boundry conditions)

    I understand that this has been answered, but I can't follow it. My apologies, physics is a realm I want to understand but it doesn't come naturally and I have no High school physics background just 1st yr Engineering physics. (passed with supps.) A particle is projected vertically upward in a...
  36. R

    Newton 2nd law, forces and vectors

    A car of mass 1000 kg tows a caravan of mass 600kg up a road which rises 1m vertically for every 20m its length. There are constant frictional forces of 200N and 100N to the motion of the car and caravan respectively. the combination has an acceleration of 1.2ms-2 with the engine exerting a...
  37. R

    Rate of change of momentum. Newton 2nd law

    rate of change of momentum. Newton 2nd law (solved) hailstones with an average mass of 4grams fall vertically and strike a flat roof at 12ms-1 . In a period of 5 minutes, 6 000 hailstones fall on each square meter of roof and rebound vertically at 3ms-1 . Calculate the force on the roof if it...
  38. J

    Problem understanding angular momentum and Newton 2nd law

    hi, thank you for any help. -[problem understanding angular momentum and Newton (second)2nd law] -[usual/classic problem of spinning bike wheel on rope doesn't fall] (from 28min:10s to 29min:15s and also 37:48 to 39:00)...
  39. M

    Newton 2nd Law word problem help

    "Newton 2nd Law" word problem help Homework Statement When the click beetle jumps in the air, its acceleration upward can be as large as 400.0 times the acceleration due to gravity. (An acceleration this large would instantly kill any human being.) For a beetle whose mass is 40.00 mg...
  40. J

    Applyings Newton 2nd Law and Kinematics

    Homework Statement A 10,000 kg rocket is acted upon by a upward thrust of 118,000N How fast will the rocket be moving after 20 seconds? How far will it have moved in this time? Also, how do i determine the net force Homework Equations a = \SigmaF/m d=1/2at2+vit The Attempt at a Solution...
  41. A

    Newton 2nd law of a fish in an elevator

    Homework Statement A person weighs a fish of mass m on a spring scale atached to the ceiling of an elevator. (a) Show that if the elevator accelerates either up or down, the spring scale gives a reading different from the weight of the fish. Homework Equations \SigmaFy=T-Fg=may...
  42. F

    Newton 2nd law + frame of reference

    hello forum, i am struggling with the conceptual understanding of this problem: Given two blocks, one on top of the other. There is friction between the two blocks. The upper block is pulled with a force F. Thanks to friction, as long as F is smaller or equal to the static friction...
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