Newton's 2nd law Definition and 136 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. L

    Newton's 2nd Law Homework: Average Force of Tennis Ball

    Homework Statement A tennis player strikes a tennis ball of mass 56.7 g when it is at the top of the toss, accelerating it to 68.0 m/s in a distance of 0.0250 m. What is the average force the player exerts on the ball? Ignore any other forces acting on the ball. Homework Equations f = ma...
  2. P

    Calculating Lift Force and Air Resistance in a Moving Helicopter

    A helicopter is moving horizontally to the right at a constant velocity. The weight of the helicopter is W = 57600 N. The lift force L generated by the rotating blade makes an angle of 21.0° with respect to the vertical. (a) What is the magnitude of the lift force in N? (b) Determine the...
  3. C

    What is the minimum acceleration of the elevator when the cord breaks?

    I have a question: Al and Bert stand in the middle of a large frozen lake (frictionless surface). Al pushes on Bert with a force of 20 N for 1.2 s. Bert's mass is 114 kg. Assume that both are at rest before Al pushes Bert. (a) What is the speed that Bert reaches as he is pushed away from Al...
  4. A

    How Do You Calculate Tension and Acceleration in a Truck and Trailer System?

    Homework Statement The 10-Mg truck hauls the 20-Mg trailer. If the unit starts from rest on a level road with a tractive force f of 20 kN between the driving wheels of the truck and the road, compute the tension T in the horizontal drawbar and the acceleration a of the rig. Homework...
  5. R

    How Does Angular Acceleration Arise in a Rotating Cylinder with Multiple Forces?

    Homework Statement http://ready2goxtr.googlepages.com/problem1055.jpg A cylinder having a mass of 2.0kg can rotate about its central axis through point O. Forces are applied as show: F1 = 6.0N, F2 = 4.0N, F3 = 2.0 N, and F4 = 5.0N. Also, r = 5.0cm and R = 12 cm. Find the (a) magnitude and...
  6. H

    How Does Newton's 2nd Law Apply to a Skateboard Pushed by a Cane?

    Homework Statement A man walking with aid of a cane approaches a skateboard (mass 3.5 kg) lying on the sidewalkk. Pushing with an angle of 60 down from the horizontal with his cane, he applies a force of 115N, which is enough to roll the skateboard out of the way. a) calculate the...
  7. C

    Newton's 2nd Law for a Particle in Uniform Circular motion

    1. A 4.0kg object is attached to a vertical rod by 2 strings. Object roatates in a horizontal circle at a constand speed 6.00 m/s. Find the tention in the upper and lower string. The strings are 2 meters long. the distance between the attachment points for each string is 3 meters. 2...
  8. L

    About force, mass, Newton's 2nd law and inertial frame

    I was reading a physics textbook. It is stated that force is defined by mass and acceleration (a force of 1N causes a mass of 1kg to accelerate at 1ms^-2). In later part, it is stated that mass is defined by force and acceleration (a mass acted by a force of 1N accelerates at 1ms^-2 is 1kg). As...
  9. M

    Newton's 2nd law in circular motion

    Homework Statement Daytona International Speedway in Florida. Both of its courses feature four story, 31.0 degree banked curves with max radius of 316 if a car negotiates the curve too slowly it tends to slip down the incline of the turn whearas if it going too fast it may begin to slide up...
  10. A

    How Do You Calculate Friction and Forces in a Skidding Car Scenario?

    Homework Statement The driver of a car whose mass is 1200kg is traveling 45km/h[W] on a slippery road when he applies the breaks. The car skids to a stop in 35m. Determine: a) the car's acceleration b) the net force acting on the car c) the coefficient of friction between the tires and the...
  11. S

    How Does Energy Conservation Apply to a Rotating Pulley System?

    Homework Statement (a) If R = 12 cm, M = 500 g, and m = 50 g (below), find the speed of the block after it has descended 50 cm starting from rest. Solve the problem using energy conservation principles. - The pulley is setup on the corner of a desk with the object hanging from it. M is the...
  12. V

    Problem involving Newton's 2nd law of motion

    Homework Statement An arrow, starting from rest, leaves the bow with a speed of 25.0m/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...
  13. B

    Angular acceleration and Newton's 2nd law

    Homework Statement A solid cylindrical disk has a radius of 0.16 m. It is mounted to an axle that is perpendicular to the circular end of the disk at its center. When a 45 N force is applied tangentially to the disk, perpendicular to the radius, the disk acquires an angular acceleration of 110...
  14. H

    Acceleration in an Elevator: Solving Newton's Second Law Problem

    Hi, I'm having trouble with a problem dealing with Newton's Second Law, and was wondering if anyone could give me a hint as to how I should solve it (general equation, process, whatever)? I'm not asking for somebody to solve it, I just need some help...:smile: Homework Statement A...
  15. L

    How Does Relativistic Motion Affect Newton's Second Law?

    Homework Statement Show that F=dp/dt=gamma^3*m*a for a relativistic system assumption: force, motion in same direction Homework Equations p = gamma*m*v(t) gamma = 1/sqrt(1-v(t)^2/c^2) The Attempt at a Solution p= v(t)*m/sqrt(1-v(t)^2/c^2) using product rule then chain rule...
  16. C

    Ideal gas law + Newton's 2nd law problem

    Homework Statement A cylinder has its lid connected to a spring with k = 2000 N/m. The cylinder is filled with 5.00 L of gas witht he spring relaxed at a pressure of 1.00 atm and a temperature of 20.0C. (a) If the lid has a cross-sectional area of 0.0100 m2 and negligible mass, how high will...
  17. K

    Applying Newton's 2nd law to single charged particle

    How much are we justified in applying Newton's 2nd law in predicting trajectories of a single charged particle?What will be the answer for a number of charges?Of course, we have cyclotron motion at hand, but still...as we know, sub atomic level physics needs quantum mechanical consideration and...
  18. L

    Collision Problem and Newton's 2nd Law

    How do car bumpers that collapse on impact help to protect a driver? According to the law of conservation of momentum, p = mv. Newton's 2nd Law is F = ma, or F = mv/t. So as t increases, F would decrease, thus less force would be acting on the car at a given time interval. Any...
  19. K

    Newton's 2nd law with an incline plane (I think help0

    Newton's 2nd law with an incline plane (I think...help0 The 1930 kg cable car shown in the figure descends a 200-m-high hill. In addition to its brakes, the cable car controls its speed by pulling an 1830 kg counterweight up the other side of the hill. The rolling friction of both the cable car...
  20. Y

    Newton's 2nd law involving pulley

    I came across some questions where one box's magnitude of acceleration differed from another box's magnitude of acceleration. Please explain why and how this can be true. Thank you.
  21. Y

    Optimal Coordinate System for Applying Newton's 2nd Law on an Inclined Plane

    (Please look at the diagram attached at the bottom) Question: Newton's 2nd law, F=ma, is a vector equation. To add or subtract vectors it is often easiest to decompose the vector into components. Whereas a particular set of vector components is only valid in a particular coordinate...
  22. K

    Need Help with Applying Newton's 2nd Law

    Need Help with "Applying Newton's 2nd Law" What is \sum F_{2x}, the sum of the x components of the forces acting on block 2? Take forces acting up the incline to be positive. Express your answer in terms of some or all of the variables tension T, m_2, the magnitude of the acceleration of...
  23. F

    Having trouble with applying Newton's 2nd Law

    Here's the problem: An object is hung from a spring balance attached to the ceiling of an elevator cab. The balance reads 66 N when the cab is standing still. What is the reading when the cab is moving upward (a) with a constant speed of 7.6 m/s and (b) with a speed of 7.6 m/s while...
  24. F

    Newton's 2nd Law problem (I think )

    Alright, here's the problem: A block is projected up a frictionless inclined plane with initial speed v0 = 7.917811929967 m/s. The angle of incline is = 36.8°. (a) How far up the plane does it go? (b) How long does it take to get there? (c) What is its speed when it gets back to the bottom...
  25. N

    Particle in Circular Motion: Newton's 2nd Law & Orbital Periods

    The position of a particle of mass m moving in a circular orbit with radius r = ro is given by: r(t) = ro <er> Show using Newton's second law of motion, that if the force responsible for this motion is given by: F = -k/r^2 <er> a) the angular velocity is constant in time, and b) the...
  26. N

    Nonequilibrium Applications of Newton's 2nd Law Problem

    I along with a buddy of mine in the same course have been trying to figure out the following question. We spent at least an hour and a half to two hours and nothing makes sense. Any help would be greatly appreciated. Here's the question as it's written: One way to measure the acceleration...
  27. R

    Newton's 2nd Law and Orbital Motion

    Here's the problem...unfortunately I don't remember much about orbital motion. I'm a bit stuck on where to begin. If somebody could give me a little advice on how to tackle this problem I would appreciate it. Recall that the magnetic force on a charge q moving with velocity v in a magnetic...
  28. K

    Calculating Force to Accelerate Lawn Mower: Newton's 2nd Law

    I figured out the horizontal friction force, Fpx to be 55.11 N and the normal force exerted vertically to be 190.8 N. And the other info given is F = 84 the lawn mower has a mass of 13 kg and moves at a constant speed. The lawn mower is at an angle of 49 degrees to the horizontal. I need to...
  29. A

    Newton's 2nd Law and a rolling ball

    Hello! I have a few homework problems that I'm just not sure what to do with: 1) A soccer ball rolls down a hill, reaching the bottom with a speed of 10.0 m/s. The coefficient of friction between the ball and the grass on the hill is .80. How far does the ball travel on the surface before...
  30. J

    How Do You Calculate an Unknown Initial Force Using Newton's 2nd Law?

    If i am given information involving a particle and I know the resulting velocity (in x and y direction) and one of the beginning forces in Newtons (x and y components as well), how do i figure out the other beginning force? I'm given no information about angles or the mass of the object
  31. F

    Newton's 2nd Law Applied to a Particle In Uniform Circular Motion

    Q. In the Bohr model of the hydrogen atom, the speed of the electron is approximately 2.20 x 10^6 m/s. Find (a) the force acting on the electron as it revolves in a circular orbit of radius 0.530 x 10^-10 m and (b) the centripetal acceleration of the electron. I'm going to...
  32. S

    Newton's 2nd Law: Why 10kg Mass Doesn't Fall Faster Than 5kg Mass

    A 10 kg mass experiences twice the gravitational force as a 5 kg mass. Why doesn't the 10 kg mass fall faster than the 5 kg mass? I never understood the reason. All I know is that Galileo found that objects dropped near the Earth's surface will fall faster with the same acceleration or g...
  33. Antonio Lao

    Newton's 2nd law is really the 3rd law?

    Did Newton accidentally reverse the order of his laws of motion? The 1st law implicitly established the notion of time and conservation of energy. The 3rd law formulated the conservation of linear momentum by m_1v_1 + m_2v_2 = constant the time derivative of this expression is m_1a_1...
  34. N

    Newton's 2nd Law Question PHYCS110

    Hey everyone~ A 2.0 kg toy locomotive is pulling a 1.0 kg caboose. The frictional force of the track on the caboose is 0.50 N backward along the track. Of the train is accelerating foward at 3.0 m/s^2, what is the magnitude of the force exerted by the locomotive on the caboose? So I'm...
  35. Antonio Lao

    Exploring Newton's 2nd Law of Motion

    Is force the cause of motion? If there is motion would there be a force also? Newton's 1st law of motion says there can be motion even without force. This motion is a constant velocity (in particular such as the constant speed of light in vacuum). Newton's 2nd law of motion says that the...
  36. J

    Find Initial Acceleration of Rod's Center of Mass with Newton's 2nd Law

    here's the question: A uniform rod of length 1.15 m is attached to a frictionless pivot at one end. It is released from rest from an angle of 27 degrees above the horizontal. Find the magnitude of the initial acceleration of the rod's center of mass. So far I've only been able to figure...
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