Third law Definition and 371 Threads

OK, first of all, I wasn't really sure where to post this; it's not really homework because we covered the material weeks ago and moved on, leaving me totally in the dark. My physics teacher has this annoying habit of saying something is "ALWAYS true" or "NEVER true" and then beginning the next...

1. A 9800kg rocket is traveling east along a horizontal frictionless rail at a velocity of 11m/s. The rocket is then accelerated uniformly to a velocity of 22m/s in a time of 0.75s by the expulsion of hot gases. What is the average force at which the gases are expelled by the rocket...

The question states: How much force does an 81.0 kg astronaut exert on his chair while sitting at rest on the launch pad? the answer that I got was 794 N using... W=m*g and Fnet=w+fchair=0 But I cannot seem to get the right answer for this second question: How much force does...

Homework Statement Two packages at UPS start sliding down a 20 degree ramp. Package A has a mass of 5.0kg and a coefficient of friction of .20. Package B has a mass of 10kg and a coefficient of friction of .15. How long does it take package A to reach the bottom? The package are positioned...

Homework Statement Hi guys i am trying to do question number 4 but i have not done a Question liek this in a very long time so i am forgetting where to start. http://img405.imageshack.us/img405/6976/101420092845.jpg" Image is to big for the forum so its easier that way. Homework Equations...

Newton Third Law problem. Help pleaseee! Homework Statement The 1.0 kg block is tied to the wall with a rope. It sits on top of the 2.0 kg block. The lower block is pulled to the right with a tension force of 20 N. The coefficient of kinetic friction at both the lower and upper surfaces of...

Homework Statement Two boxes are in contact with each other, both different mases, and are both being pulled by an external force, F. M1M2--------->F I can calculate the acceleration of the system but the Question asks to calculate the force between the mases, ie Newtons third law. If...

Hello, Few questions about these things.This is not homework! 1. Is Newton's 3rd law caused by conservation of momentum? 2. If I drop a stone into a pond. The stone would exert a force on the water and the water would exert a force on the stone. So why doesn't the stone move up! 3. Is...

So there's this guys argument that Newtons 3rd law is wrong: "When I say that for every action there CAN'T be an equal an opposite reaction, it is a FACT. It's mathematically IMPOSSIBLE to have an EQUAL reaction to every action. Because then NO action would succeed. ALL actions would be right...

Jenny and Betty are having a great time at Busch Gardens riding the Ubanga Banga bumper cars. Jenny, who is traveling southward in her bumper car, aims her car toward Betty, who is traveling northward in her bumper car. The cars collide and briefly come to a stop. 1)What is the direction of...

Consider a toroidal solenoid powered by a sinusoidal voltage. This will lead to appearance of sourceless electric field, also sinusoidally varying with time. Now consider a conductive ball in the center of the system. Let the electric charge on the ball vary in phase with the voltage applied to...

Homework Statement Two buckets of nails are hung one above the other and pulled to a roof by a rope. Each bucket of nails has a mass of 5.0kg. The action-reaction force between the buckets is 60N. Calculate the acceleration and the force applied by the worker lifting them up. Given: (draw a...

Greetings the venerable PF society, I have a question that has been lingering in my mind for a while, so I thought I'd ask it here. Firstly, how far below does the action-reaction (Newton's third law) principle go down fundamentally? How far below can I take it with me so that I don't make...

Homework Statement "Three blocks (m1, m2 and m3) are in contact with each other on a frictionless, horizontal surface. A horizontal force is applied to m1. http://i4.photobucket.com/albums/y111/kathy_felldown/sb-pic0556.png What is the net force on block 1? " When drawing free body...

Homework Statement A 5.9 kg box is on a frictionless 40 degree slope and is connected via a massless string over a massless, frictionless pulley to a hanging 2.1 kg weight. A. What is the tension in the string if the 5.9 kg box is held in place, so that it cannot move? B. If the box is...

I have heard that Newton's third law fails to apply in certain cases. Is it true?? and if it is , is there a reason why it works in the remaining cases? also regarding the second law F=dp/dt is it how force is defined ??or is it a relation between force and change in momentum?? if it is...

Homework Statement would you say that "the two forces exerted on the book ar ethe normal force directed up and the weight of the book directed down. These are equal and opposite to one another. By Newton's third law they are a third law force pair, so the normal force is always equal to the...

How can two objects of different mass accelerating at the same speed impart an equal an opposite force on each other when they collide? I understand Force to be equal to Mass times Acceleration. How can the Force and Acceleration be equal while the Masses are different? I'm probably...

Homework Statement By considering the centripetal force which acts on a planet in a cirlar orbit, show that T^2\proptoR^3, where T is the time taken for one orbitaround the Sun and R is the radius of the orbit. Homework Equations Fc=GMm/r^2 1/2Mv^2=GMm/r^2 The Attempt at a Solution...

A thought-experiment. (This is not homework!) Supposing someone puts a radio-controlled helicopter in a CLOSED clear-plastic box. They then put the box plus chopper on a sensitive scale and recorded the weight. Say 50N for the sake of argument. Now suppose they started up the chopper and...

Well i known this is a kinda fundamental property of mechanics but i always have a weird thinking about this law. Let me illustrate my trouble with an example. Let's say i kick a ball with force F? According to the Law the ball experience F force, and my leg experiences -F. My questions...

I am so very confused by this third law business. It all started with me thinking about whether it is true that heavy and light objects fall at the same rate (I don't mean approximately). I figured that they don't. While the Earth attracts, say, an elephant and a small rubber ball, at the...

Homework Statement I am studying gravitation and I have been trying to derive Kepler's Third Law using Kepler's Second Law.Homework Equations The second law : \frac{dA}{dt} = \frac{L}{2m}The Attempt at a SolutionTo start with, I thought if we take \int \frac{L}{2m}dt from 0 to T; we would...

Suppose I have a proton at the origin, and a (stationary) electron on the x-axis at x=r. Taking q to be the elementary charge, the force acting on each of these particles is: F = \frac{q^2}{r^2} Now suppose that the electron is heading towards the proton (in the negative x-direction)...

Found the following statement on the web: You can't hit a feather in midair with a force of 200 N because the feather is not capable of exerting a 200 N force on you. The forces "you hit feather" and "feather hits you" are a Newton's Third Law action/reaction force pair, so they must always be...

Homework Statement Two blocks are accelerated across a horizontal frictionless surface as shown. The coefficient of static friction between the two blocks is 0.7, and the coefficient of kinetic friction is 0.5, use M= 1.0 kg. When F=1.2 N, frictional forces keep the two blocks from sliding...

Hello PFers, I've been reading these forums for a little while, and now that I have my own question I thought I would register to the site :). My question is about pumping and Skimboarding. I understand that many of you (if not all) have no idea what skimboarding and pumping even is...

Hello, True or False: - According to Newton third law, the algebraic sum of the forces in the system is equal to zero. I think the answer is FALSE because, the third law of Newton says that F1 = - F2 and the " - " is for the direction, so that F1 = F2 in the quantity ==> F1 + F2 \neq 0

Homework Statement How does Newton's Third Law of Motion apply to a tetherball? Homework Equations N/A The Attempt at a Solution Forces always occur in pairs (action/reaction force). I know that when you're pushing on a wall, the wall pushes back on you, which is why you don't...

Why do rockets behave so well in accordance to Newtons third law

This is more of a conceptual question, meant to help us understand how tension forces work. Homework Statement Assume that segment R exerts a force of magnitude T on segment L. What is the magnitude FRL of the force exerted on segment R by segment L? Give your answer in terms of T and other...

Homework Statement A physics student in a hot air balloon ascends vertically at a constant speed. Consider the following four forces. that arise in this question. F1 = the weight of the hot air balloon F2 = the weight of the student F3 = the force of the student pulling on the earth F4...

Homework Statement there is a pulley and on one side there's a man hanging on it he weights 60kg on the other side resting on the ground is a 100kg weight. what is the tension on the rope Homework Equations T-m1g=m1a T-m2g=m2a F=2T-(m1+m2)g The Attempt at a Solution T-m1g=m1a...

Homework Statement You are standing on scales which read weight in Newtons. A 0.50 kg ball is dropped from a height of 1 m into your hands. Your hands drop from chest level to waist level during the catch, a distance of about 25 cm. Your mass is 62 kg. Assuming that you decelerate the ball...

Ok so I just read this statement as part of an explanation of list using Newton's 3rd law "The amazing thing about wings is that because they are flying through air which is a fluid, the top of the wing deflects air down as well as the bottom of the wing." What I don't understand is how...

If everyone believes that there's an equal and opposite reaction for everything, should the universe go out to a point and stop; or will it end up coming back to its origins?

Hey guys, was just wondering if you could explain the answer to this question. So basically we have a picture of a book resting on a table. On this book there is the weight force downwards and the reaction force upwards, both acting on the center of mass. The question: A class of students is...

The lower block in the figure is pulled on by a rope with a tension force of 20 N. The coefficient of kinetic friction between the lower block and the surface is 0.30. The coefficient of kinetic friction between the lower block and the upper block is also 0.30. What is the acceleration of the...

The figure shows two 1.0 kg blocks connected by a rope. A second rope hangs beneath the lower block. Both ropes have a mass of 250 g. The entire assembly is accelerated upward at by force. What is F? What is the tension at the top end of rope 1? What is the tension at the bottom end of rope 1...

[SOLVED] Newton's third law Homework Statement My book gives two forms of Newton's Third Law: Weak Form: The forces exerted by two particles \alpha and \beta on each other are equal in magnitude and opposite in direction Strong Form: The forces exerted by two particles \alpha and \beta on each...

Homework Statement In a tractor pulling contest, a 2300-kg tractor pulls a 4900-kg sledge with an acceleration of 0.61 m/s^2. If the tractor exerts a horizontal force of 7700 N on the ground, determine the magnitudes of (a) the force of the tractor on the sledge; (b) the force of the sledge...

Ok, I'm getting a lot of mixed messages about the reactionary forces involved with the 3rd law. if i push a box at a constant speed with 100N of force, is the friction that resists the motion the opposite but equal (100N) reaction force? isn't the friction force LESS than the push force because...

Hey guys, I was just wondering if you could help me with a question that has been bugging me for a while now. I've thought of many possibilities to the answer yet i still can't find the right one. The question is that, when a fly strikes the windshield of a truck moving at let's say 60km/h, why...

[SOLVED] Newton's Third Law problem Homework Statement Three boxes, A, B, and C, are positioned next to each other on a horizontal, frictionless surface. An applied force acting on box A causes all the boxes to accelerate at 1.5m/s^{2}[right]. Calculate the force that box B exerts on box A...

[SOLVED] Newton's Third Law problem Homework Statement Three boxes, A, B, and C, are positioned next to each other on a horizontal, frictionless surface. An applied force acting on box A causes all the boxes to accelerate at 1.5m/s^{2}[right]. Calculate the force that box B exerts on box A...

Hi all, I would like to know in which circunstances the third law applies just in the weak form. Thank you DaTario

I am reading Introduction to Mechanics by Kleppner and Kolenkow. I am now reading the articles dealing with conservation of angular momentum. I am not satisfied with the articles dealing with how the third law does not lead to conservation of angular momentum. Could anyone please throw some...

Homework Statement I have this problem for homework and I don't know how to even start. Can someone help? Thanks in advance.A neat and exploitive use of the sun would be to put a space probe into a solar elliptical orbit from the Earth on one side of the sun headed towards a rendezvous with...

I have spent a ton of time researching my question but i can't find the answer i know that for every action there is an equal and opposite reaction i know if you have a tire on the ground and when it starts spinning it pushes so that the concret will go the other way but the ground it to...

It says that every reaction there is a opposite and equal reaction. Why do things still move if everything is opposite and equal?