# What is Newtons law: Definition and 97 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. ### Verifying that Newton's Equations are equivalent to the EL equations

In the past, I have shown relatively easily that if we have a lagrangian of the form ##\mathcal{L}=\frac{1}{2}\dot{\mathbf{q}}^2-V(\mathbf{q})## simply plugging this into the EL equation gives us newtons second law: ##\ddot{\mathbf{q}}=-\frac{\partial V}{\partial \mathbf{q}}##. I am unfamiliar...

3. ### A box with the mass m = 25 kg is sliding up a hill

What I have already attempted is on my Ipad and I don't know how to upload it on here. With hope of help DJ
4. ### A dial can spin on a fixed rotational axis

What I have done is on my Ipad that I cant upload or at least don't know how to... :/ With hope of help DJ
5. ### Analysis of a deformable body and Newton's 3rd Law

I'm posting the images of "Sommerfeld's Lectures on Theoretical Physics, Vol 2, Mechanics of Deformable Bodies" I apologize for posting the images rather than writing out the whole thing. But I did it to so that nothing should be missed, as writing out the...
6. ### Freefall v Jetpack: Will He/She Stay Afloat or Crash?

Homework Statement There is a random person falling from the sky. He remembers that he has a jetpack. Unfortunately, his jetpack is weak and is only able to provide upward force equivalent to Fg. WILL HE?SHE STAY AFLOAT OR WILL HE?SHE CRASH INTO THE GROUND? What acceleration will he/she hit...
7. ### Free Fall vs Jetpack: Will He/She Stay Afloat?

There is a random person falling from the sky. He remembers that he has a jetpack. Unfortunately, his jetpack is weak and is only able to provide upward force equivalent to Fg. WILL HE?SHE STAY AFLOAT OR WILL HE?SHE CRASH INTO THE GROUND? What acceleration will he/she hit the ground?
8. ### Question about inertial and non inertial frames

Suppose a person A is standing in a bus and bus is accelerating forward then when a person B standing outside observes A he see that A is accelerating in forward direction then there must be a force acting on him which is making him accelarating(because Newtons first law holds in Earth's frame)...
9. ### A few questions related to tension in a string

Its getting hard for me to deal with the problems related to tension and reason behind this is not clear understanding of the concept so i have few questions on this. What causes tension in a rope/string(i think its related to electromagnetism, but i am not getting the clear idea behind this)...
10. ### Analysis of tennis string tension

I have a decent background in physics, but something that has always confused me is how to think about how the tension of the string in a tennis racquet affects how the ball leaves the strings. For example, the traditional lore in tennis is that tauter strings will give more control, whereas...
11. ### Sphere rolling with slipping on a movable platform

Homework Statement A sphere (of radius r and mass m) rotating with angular velocity ω0 is lowered onto the edge of a floating platform of length L and mass M. The platform can move freely on water. The platform is rough and the sphere rolls all the way from one edge to the other edge of the...
12. ### Investigating Net Force in Two Dimensions

Homework Statement Homework Equations no equations required The Attempt at a Solution i already answered the question, but i just want to know if i wrote the right direction for the Fnet. is it [N 10 W] or [W 10 N]?[/B] this is how i wrote it: Fnet: 1165 N [N 10 degrees W]
13. ### Apparent weight loss 2nd Newtons Law elevator problem

Homework Statement A 65-kg woman descends in an elevator that briefly acclerates at 0.20g downward when leaving a floor. She stands on a scale that reads in kg. (a) During this acceleration, what is her weight and what does the scale read? Homework Equations ƩF = maThe Attempt at a Solution I...
14. ### Net Force on 5.32 x 10^4 kg Airplane: Solve the Mystery

Homework Statement An airplane with a mass of 5.32 x 10^4 Kg accelerates down the runway at 1.76 m/s^2 [forward]. Calculate the net force acting on the airplane. Homework Equations Fnet=ma The Attempt at a Solution I did this by multiplying the two given values, but my answer was 93632N...
15. ### Mastering Newton's Laws for 9th Grade Talent Exam: Overcoming FBD Problems

I have been preparing for a 9 Th grade talent exam and i can get my head around this problem I keep getting the same answer 5, i used fbd The answer is 7 ; help me out where am i wrong
16. ### Newton's law problem on homogeneous flexible rope

Homework Statement A homogeneous flexible rope rests on a wedge whose sides make angles α and β with horizontal. The centre of rope lies on C. With what acceleration should the wedge be moved for the rope to stay stationary with respect to wedge? (all surfaces are smooth). Homework Equations...
17. ### Projectiles and Newtons law help?

The first question is about Newton's Third Law: A boat is moving north at a velocity v=15 km/h a man on the boat throws a ball horizontally with a velocity u=15 km/h how is the motion of the ball w.r.t the man? For this, I thought that because the boat is moving with the same speed as the...
18. ### Finding coeffiecient of friction

Homework Statement You give a 2.85kg book an initial shove at 2.98m/s and it comes to rest after sliding 3.80m across the floor. Find the coefficient of friction between book and floor. Homework Equations vf^2=vo^2+ad f=ma The Attempt at a Solution 0=2.98+a*3.8 =2.33
19. ### Frame of reference and Pseudo forces

If you have a car and a pendulum is hanged inside it, and if you watch from outside the car,and if the car has some acceleration, then you see the bob moving in opposite direction of motion of car. For a person standing outside, he knows that the car has some acceleration. What causes the bob...
20. ### Help to understand Newtons Law

Homework Statement I am trying to understand a diagram I have of a gymnast hanging from a bar. She weighs 50kg and is not swinging, just hanging. In the diagram it has her weight as 500N (using 10/m/s/s for gravity * 50kg) but the bar she is hanging from has an upward arrow with 550 N next to...
21. ### Free body diagram and applying Newtons law

hello! this is a question that iv been working on and can't seem to figure it out, i checked out the other two threads on this same question but they were of no help, anyway here it is: A wedge with mass M rests on a frictionless horizontal table top. A block with mass m is placed on the wedge...
22. ### Newtons law of gravity problem

Homework Statement Two identical rocks of mass 2 kg drift through space far from any planet or star. If they pass one another at a separation of 30 cm, what is the magnitude of the gravitational force of one rock on the other at this instant. Homework Equations F = G (m1m2/r2)...
23. ### Newtons law and canoe question

If you can get to your feet in a canoe and move towards the front of the canoe, it will move in the opposite direction. Explain why. I thought Newton's first law applies to this question (after the person steps on the canoe, the canoe still maintain at rest), but i am not sure how to explain it.
24. ### Can You Solve This Newton's Law of Motion Problem?

To Admin - This is not my homework, My teacher solved it but I am trying to solve this problem using other methods. If I posted this in wrong group, please message me and I will Post this in correct corner. Problem - To find acceleration in both blocks sliding on smooth surface,string and...
25. ### Using Newtons law and mechanical energy?

1. Homework Statement [/b] A car is rolling down a ramp that is inclined at and angle of 9.9 degree with respect to horizontal. There is no friction acting from the road on the tires. Employ conservation of mechanical energy to find the speed of a car that starts from rest and rolls down...
26. ### How Do Friction and Normal Force Act on a Rod at an Angle?

Homework Statement Here is a rod of mass m(as shown in figure)which is released from rest.The angle made by the rod with the ground is 600. Assume that the force of friction is enough to prevent sliding of the rod.Find the normal reaction and the frictional force just after the rod is...
27. ### Fluid Mechanics Newtons law of viscosity

Homework Statement having problems differentiating Homework Equations Tw ( wall shear stress)= -U(viscosity)*du/dr been given u as 2V(1-(r/r)^2) The Attempt at a Solution i substituted u in and got d/dr (2V(1-(r/r)^2) i tried to multiply out the minus sign and 2V and got...
28. ### Newtons law Dynamics Question 4

Homework Statement Determine the acceleration of a 10kg block traveling up a ramp connected by a massless string and massless pulley to another block that is 5kg and in free-fall. if the coefficient of kinetic friction between the block and the ramp is 0.2 (The diagram shows one block...
29. ### Differential Equation Involving Newtons Law of Motion

Homework Statement mv'=-gm-kv Find the position function using the initial coniditions of t=0 for all Constants Homework Equations Reverse product rule The Attempt at a Solution My attempt is on my white board. Its attached as a picture.
30. ### Three blocks Newtons law help have I got my answers and sign correct ?

Three blocks, each of mass 7.0 kg are on a frictionless table. A hand pushes on the left most box (A) such that the three boxes accelerate in the positive horizontal direction as shown at a rate of a = 1.1 m/s2. What is the net horizontal force on block B? =15.4 N What is the horizontal...
31. ### Projectile Motion Calculations for a Shell Fired at 30 Degrees

Homework Statement A shell is fired at an abgle of 30 degrees to the horizontal. If the shell stays in the air for 40 seconds, calculate a)how far it lands from it's original position b)the highest point it can reach Homework Equations N/a The Attempt at a Solution I was...
32. ### Plateau equation from Newtons law

Homework Statement The Plateau equation (minimal surface of a soap film) can easily be derived from variational principle. We want to minimize the area of the soap film, S = \int \sqrt{1 + z_x^2 + z_y^2} \, \mathrm{d}x \, \mathrm{d}y , and through Euler-Lagrange equation we get the...
33. ### How Much Force Is Needed to Prevent the Smaller Block from Falling?

Homework Statement The static friction between the two blocks is .47 and kinetic friction between the block with mass 9.4 kg and the horizontal surface is 0.21.The acceleration of gravity is 9.8 m/s^2 What is the minimum force F which must be exerted on the 9.4 kg block in order that the 0.8...
34. ### Newtons law of cooling vs conduction equation in solids

I know that Newtons law of cooling is useful when a solid is transferring heat to a fluid. And conduction equation is used in solids. My question is: 1) Can Newtons law of cooling be applied in case of solids (apart from Heat conduction equation)? 2) Can Newtons law of cooling be applied in...
35. ### Does Newton's Law of Gravitation Account for Horizontal Surface Area?

Hello, Is there any research available as to whether Newtons Law F = mg should include horizontal surface area as a factor (ie the surface area of opposing masses). Example a pole weighing exactly the same seems heavier when held at one end horizontally to the ground, compared to holding it...
36. ### Need help on this question on Newtons law of cooling

Homework Statement please i need help as have been trying to solve this question: A body cools from 70°C to 50°C in 6mins when the temp of the surrounding is 30°C. what wil be the tempt of the body after another 12mins if the cooling obeys Newtons law of cooling equation: dq/dt =...
37. ### Are Newton's Laws Applicable to Component Forces and Resultant Acceleration?

Homework Statement I just wanted to know if I was correct, when dealing with a Newton law problem that has components. Ʃfx=0 and ƩfY = zero However when we add the forces together then we can use Ʃf=ma thanks Homework Equations The Attempt at a Solution
38. ### How Does a Motorcycle Exert Force Backward to Accelerate?

Homework Statement A 245 kg motorcyle & rider can produce an acceleration of 3.50 m/s sq while traveling at 25 m/s. At that speed, the forces resisting motion (friction & air) total 400 N. What force does the motorcycle exert backward to produce it's acceleration? Homework Equations...
39. ### Newtons Law of Cooling - Determine rate of cooling

An engine switched off and left to cool naturally will obey Newtons law of cooling. A particular engine is switched off at 105°C when the ambient temperature is 0°C. Its temperature falls according to the equation T=105e-0.025t °C. Where t=time in minutes. c) use calculus to determine the...
40. ### Is Newtons law of cooling related to the zeroth law of thermodynamics?

Being that both laws explain some kind of heat transfer I was wondering if they are in any way related.
41. ### Thermo: Newtons law of cooling for radiation

Homework Statement A cube of copper of mass 4 kg and initial temperature of 110 oC is set to radiatively cool in an environment of 100 oC. (Note: copper has an emissivity of about 0.05. Also, neglect conduction and convection as cooling agents in this problem.) The surface area of the...
42. ### Newtons Law Problem involving kinematic equation

Homework Statement A duck has a mass of 3.0 kg. As the duck paddles, a force of 0.06 N acts on it in a direction due east. In addition, the current of the water exerts a force of 0.13 N in a direction of 60° south of east. When these forces begin to act, the velocity of the duck is 0.12 m/s...
43. ### Calculating Friction Forces in a System of Blocks Connected by Cords

Homework Statement Homework Statement the blocks shown in the figure are connected by flexible, inextensible cords passing over frictionless pulleys. at A, the coefficient fiction is 0.30 while at B, it is 0.40. compute the magnitude and direction of the friction forces and each block...
44. ### How Do You Calculate the Forces in a Tug of War?

I need to find the magnitude of the force exerted from one boy onto another in a game of tug of war and vice versa. Peter weighs 539 N, John weighs 392 N. During the course of the game Peter accelerates at a rate of 3.0 m/s^2. First the magnitude of force Peter exerts onto John. Then the...
45. ### Newtons Law of Cooling applied to hot Neon and Hydrogen gas

Homework Statement 1 mole of Hydrogen gas at 300 Kevin is contained in a thin walled copper container. In container #2 there is 1 mole of Neon gas also at 300 Kevin. The volume= 22.4 liters and surface area ,A = .476 m^2 The surroundings are at 100 deg Kelvin. The specific heat of H2= 5...
46. ### Missing something (Newtons law)

Hello there! I'm trying to solve this in two ways, and i keep getting different solutions. I need to find the force by which M should be pushed for m1 and m2 stand still (compared tom M). There is no friction between anything. First solution: F_{rp} = m_2 \cdot g \: \: \: F_{rp} = m_1...
47. ### Calculating Friction and Acceleration for a Grocery Cart on an Inclined Plane

Homework Statement a grocery cart is being oused with a force of 450 N at an angel of 30degree to the horizontal. if the mass of the cart and groceries is 42kg. a) calculate the force of friction if the coeffcient of friction is 0.60. b) determine the acclecration of the cart...
48. ### Two body applications of Newtons law of cooling.

Homework Statement What's the formula that better describes the temperature as a function of time for an enclosed body of water with certain initial temperature T_a immersed in another body of water of initial temperature T_b? More clearly, I performed an experiment in which I put a...
49. ### Newtons Third Law and Force Imbalance

Homework Statement 1.A 140 kg man pushes a 90 kg man. They are first motionless, as they push larger man moves smaller one backwards. which statement is correct. a)forces are always equal b) larger wrestles always exerts larger force c)when they are motionlesss forces are equal but as they...
50. ### Understanding and Applying Newton's Law of Cooling

Homework Statement Newton's law of cooling says that the rate at which the emperature of any object changes is proportional to the temperature difference between the object and its surroundings. So if the temperature of the object is T, and its surroundings are at a constant temperature...