What is Newton's third law: Definition and 251 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.
An alternative title could have been "how do forces propagate" but google searches bring up things related to waves only.
Initially my problems started with a mass on a spring but I was able to boil it down to any general system comprising at least two 'parts' in succession.
Suppose you have...
C. There is no net change in force, momentum, or velocity of the sail craft because the fan exerts a forward force on the air; however due to Newton's third law the air exerts an equal and opposite force on the fan. This air then exerts a forward force on the sail which cancels out the rearward...
This problem is from MIT's module again.
I have a doubt about Newton's Third Law. How is the normal and weight of the book not Newton's 3rd Law pairs?
When the book is placed on the table, I imagine that the book's weight exerts a force on the table and the table exerts and equal and...
Something about Newton's third law confuses me, when I hold my phone and I move it around it's velocity is changing, therefore because Newton's first law it's acted on by a force, and because Newton's second law, the force is directly proportional to the mass and acceleration of that object...
Hi, here's a theoretical problem that I am trying to find a satisfactory answer for.
Imagine a coil that is temporarily switched on an off and generates a magnetic field that permeates through space. Now imagine a charged particle passing through this field, at time that the coil is already...
I have gathered that forces always occur in pairs and are equal in magnitude but opposite in direction and that according to the second law a force is the product of the mas and acceleration of the object exerting the force.
My problem is with getting this make sense with real life examples. If...
Since the airplane is flying at a constant speed, then the lift force equals the weight of the airplane. This means that the lift force prior to acceleration is the mass * gravity constant = 29400 N.
When the airplane increases horizontal speed, the lift force increases to 30 kN. This means...
eg. For a ball in free fall (ignoring air resistance) there is only one force acting if the system is just considered to be the ball. It seems necessary to go to the system which includes the Earth for identification of the reaction force to be made. Is there any rule for how big a system must...
for c) i need help
d)
Given: Let [forward] be positive.
F 1 = — 250 N
F 2 = 360 N
Unknown: a = ?
Equation: F net= F1+ F2
F net= m a
Solve: F net= (— 250 N) + 360 N = 110 N
F net= m a
a = F net/ m
= 110 N / 220 kg= 0.5 m/s [forward]
Statement: The acceleration of the boat is 0.5 m/s [forward].
For example, let's say i have force acting on an object about some pivot. That object will apply an equal force about the same pivot, at equal lever arm, back. So there it seems like if the forces are in line, acting on the same pivot point, there is an equal and opposite torque.
However, if i...
Is third Newton law valid for rotation / Torque? I mean, can we say that for every torque there must be another torque with equal magnitude and opposite direction?
This can only be true for contact forces or radial forces, as these forces will create a reaction that will cancel the torque...
Let us consider two point charges: one of which moves (in the simplest case) rectilinearly with a constant speed and the other is at rest. The electric field of the first charge is renormalized due to the effects of retardation and generation of a solenoidal electric field (see Am. J. Phys...
I know that the normal force and Fg are unbalanced in this case, but I don't get how to set up the equilibrium equations with that. I struggle with determining what you set the equations equal to when its either balanced or unbalanced forces you're dealing with.
Thank you very much your time!
I first found the force of the air on the boat using the principle of Newton's third law and the fact that no friction is involved.
Faction= -Freaction
150 N backwards = -150 N backwards
150 N backwards = 150 N forward
I then sought to determine the...
m1 is the large cruise ship
m2 is the tug boat
The question doesn't state it explicitly, but I assume that both masses are undergoing acceleration because the tug boat is experiencing a change in velocity. I assume the system accelerates uniformly, and I assume that m1 and m2 accelerate...
1. Drawing Free Body Diagrams for all components we get :
2. Following this we can find total elongation using ##\Delta L = \frac {1}{AY}(F_1*L_1 + F_2 *L_2+ F_3 *L_3) ##
My questions :
a) I am assuming that the internal forces (3t) are neglected in the FBD because of Newton's third law whereby...
Homework Statement
A spherical rubber balloon inflated with air is held stationary, with its opening, on the west side, pinched shut. (a) Describe the forces exerted by the air inside and outside the balloon on sections of the rubber.
Homework Equations
?
The Attempt at a Solution
The air...
Homework Statement
Two blocks are attached to opposite ends of a massless rope that goes over a massless, frictionless, stationary pulley. One of the blocks w/ a mass of 1.5 kg accelerates downward at (3/4)g.
A. What is the mass of the other block?
Homework Equations
There were no given...
Hi everyone. I found this image online that made me question a couple of things that might be a bit humiliating to ask:
I always thought that tension is simply a pulling force, meaning that the mass is suspended because the tension force pulling the mass is equal to the weight force of the...
Homework Statement
On a horizontal frictionless floor, a worker of weight 0.900 kN pushes horizontally with a force of 0.200 kN on a box weighing 1.80 kN. As a result of this push, which statement could be true?
A ) The box will not move because the push is less than its weight.
B ) The worker...
Hi everyone, I am new to this forum, and I'm having a hard time understanding Newton's third law and collisions, first of all I want to say that it is not homework and that I do know the basics of physics, vectors, energy, work, and momentum I also know and understand Newton's first and second...
The following reasoning leads to an apparent paradox; explain what’s wrong with the logic. A baseball player hits a ball. The ball and the bat spend a fraction of a second in contact. During that time they’re moving together, so their accelerations must be equal. Newton’s third law says that...
Homework Statement
A book is placed on a chair which is standing on the floor. An iPad is placed on the book. The floor exerts a significant force:
A) only on the book
B) Upwards on chair and downwards on book
C) ONLY upwards on chair
D) upwards on chair book and iPad
E) downwards on...
Homework Statement
A 2,300 kg truck pushes a 2,500 kg SUV, and they both move at 3.75 m/s2. I am to find the force that the SUV exerts on the truck.
Homework Equations
F=ma
The Attempt at a Solution
I solved this problem already, it was just taking the acceleration I had found (3.75) and...
Can someone clarify this for me-- how is the motion of the center of mass unaffected by internal forces, as is stated towards the end of the paragraph in the picture I've provided. It seems to me that motion of the center of mass directly affected by these internal forces. Specifically, the...
Hello,
1- IF we have an object has 200 kg and we also have a machine has 5 kg and pushes that object with force of 600 n , in Newton third law it must be another force =-600n then : the acceleration of the object must be 3 m\s^2 and the acceleration of the machine is 120 m\s^2 , Am I wrong...
<Moderators note. Moved from the quoted thread to avoid detracting>
Newton third law does apply in magnetism, and this is proved by applying the conservation of momentum principle. This will be clearer when the causes/origin of the magnetic force is understood as described in the work "Two new...
Homework Statement
A group of construction workers are building a house and want to lower down an excess bundle of 1400 kg bricks to ground. They tie one end of a rope to the bundle of bricks, loop it through a pulley, and tie the other end of the rope to a toolbox. If the coefficient of...
Homework Statement
If every action has an equivalent and opposite reaction, how is that anything ever happens ?. Shouldn't force pairs equal in magnitude cancel each other?
Homework EquationsThe Attempt at a Solution
I tried drawing a free body diagram, but it didn't help much. This is a...
how can you say(prove) that Newton's third law is frame independent. you will say that as real forces are frame independent , therefore Newton's third law is also frame independent, so tell me how real forces are frame independent?
Hello, I am Awais gul, a student of science subjects and learning the basic of Physics , chemistry and computer science.I have a Question about Newton's third law of Motion.
Question : If we Throw a ball on a wall it goes back but if we throw a ball on sand why it does not go back?
Newton's...
Imagine that I am pushing on a wall. Then my textbook says that by Newton's third law, ##F_{AB} = F_{BA}##, where I am B and the wall is A. Isn't this wrong? Shouldn't it be that ##F_{AB} = -F_{BA}##?
I've been noticing that there are exceptions to every scientific law. For Example, with Newton's First and Second Laws are totally invalid at the quantum level, but I'm failing to find such an example for Newton's Third Law. Is anyone able to help me?
Homework Statement
Use Newton's third law to explain how a rower makes his rowing boat move forward through the water.
Homework Equations
no equations required
The Attempt at a Solution
According to Newton's third law, there is a reaction force for every action force. In this case, the...
I am not the best at drawing, I know.
If A exerts a force of 200N on B, then by Newton's third law, 200N would be exerted on it. Similarly, if B exerts 100N on A, by Newton's third law, 100N would be exerted on it. Then why wouldn't both accelerate in opposite directions with accelerations equal...
This is probably a very trivial question, but my brain isn't "playing ball" today so I'm hoping someone can help me with this.
Suppose I have a system of ##N## mutually interacting particles, then the force on the ##i##-th particle due to the other ##N-1## particles is given by...
If an apple hanging in the tree has only reaction upwards, then what will happen to a Newtons third law? how is it that there is no "force " downwards, but have spacetime curvature which "mimics" a force. why can't spacetime curvature be itselt a force?
Homework Statement
In terms of Newton's Third Law, why is it better for 2 cars of the same mass, both going 50km/h to crash into each other than for 1 car going 100km/h to crash into a wall?
Homework Equations
Newton's Third Law
F=ma
The Attempt at a Solution
I have no idea. I'm really confused
Homework Statement
Hello,
Regarding the idea of Newtonian force pairs, imagine a bottle resting on a table:
Weight force exerted on bottle by Earth and normal contact force on bottle by table are not Newtonian force pairs because they are different types and act on the same object.
Weight force...
Homework Statement
Explain why when a person in a canoe throws a package onto the shore, the canoe moves away from the shore?
Homework Equations
No equations, just Newton's third law.
The Attempt at a Solution
I think it's because the person applies a force onto the package and the package...
let's look at force at the atomic level to understand the Newtons third law of motion. I'll use Helium atoms as an example.
Now imagine we start with one atom HE2 stationary, and throw another atom HE1 at it.It is the velocity of HE1 that affects the motion of HE2 , because the system of these...
Homework Statement
Emma and Caleb are playing a game. I don't know what the name is, but they put their fingers together like a hook and then pull. Caleb won. does that mean that Caleb pulls with greater force than Emma pulls him? Caleb wins. Does it mean that he pulls with greater force than...
Hey guys, I have some confusion with Newton's Third Law. I understand that, for example, if I push against a wall the wall feels my force and the wall puts an equal force onto me.
One confusion comes from the horse cart problem, or any motion problem that uncludes one object pushing another...
The Newton's third law states that the force exerted by body A on body B is equal to the force exerted by Body B on Body A . In this case, isn't the object supposed to be stationary because equal forces are acting on both sides?
Can someone please explain to me . Thanks
Homework Statement
I need to explain why I can't lift myself by pulling my shoes' laces.
Homework Equations
Newton's third law
The Attempt at a Solution
My explanation is that by pulling on your laces, there is always going to be a force that goes against your force, so this is why you...