What is Newtons third law: Definition and 53 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.
Its clear in elastic collision that both KE and momentum is conserved. Bodies exchange their velocities. It is seen clearly in this video. There is no decrease in speed. Total KE is constant.
But in an inelastic collision momentum is conserved again but not the KE. There is loss in KE (I guess...
Hello everyone.
Probably this question is trivial, but nevertheless I am confused about Newtons law of motion:
$$F=G\frac{m_1m_2}{r^2}$$
Now, some sources say, that F is the force between the two masses m1 and m2. Other sources say, that F is the force that m1 exhibits on m2. But isn’t this a...
Homework Statement
A locomotive has broken through the wall of a train station. During the collision, what can be said about the force exerted by the locomotive on the wall?
a)The force exerted by the locomotive on the wall was less than the force exerted by the wall on the locomotive.
b) The...
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...
Homework Statement
[/B]
A child sits on a sled (50kg) on a snowy hill with an incline of 5 degrees. The coefficient of static friction is 0.05. What downward force must a parent apply parallel to the normal force, to prevent the child from sliding down the hill? (Answer: 366N)Homework Equations...
okay, so I’ve had this random thought. We have all been told that objects fall to the ground at the same speed, even if they have different masses. While it’s true that any two objects, regardless of mass, will accelerate towards Earth at the same speed, that doesn’t mean the Earth is...
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...
so i am literally one step away from producing a floating skateboard powered by permanent magnets,
so here's what i wanted to check, to make sure I haven't missed anything obvious
vertical lift achieved by using vertical repelling fields
rotational motion is controlled by counterbalancing the...
Homework Statement
Two people each with a mass of 70kg are wearing in line skates and holding opposite ends of a 15m rope. One person pulls forward on the rope by moving hand over hand and gradually reeling in more of the rope. In doing so, he exerts a force of 35N (backwards) on the rope. This...
Hello.
First, look at the figure describing Carnot's cycle.
In 1st step (A → B) and 2nd step (B → C), I fully understand that the work done on the pistol (surrounding) by the gas (system) is dW = pdV where dV = Adl since F = pA is the only force on the pistol from the gas (I assumed there...
Given a certain situation, how do you figure out the force that will be exerted onto something (you can only use F=ma to find the average net force over a certain time period, and only after you know the acceleration)? For example, if you have a non accelerating object colliding with another non...
Homework Statement
A 400 g steel block rotates on a steel table while attached to a 1.20 m -long hollow tube. Compressed air fed through the tube and ejected from a nozzle on the back of the block exerts a thrust force of 4.91 Nperpendicular to the tube. The maximum tension the tube can...
Homework Statement
[/B]
Three blocks move on a frictionless surface and a 42N force acts on the 3kg block.
The force exerted by the 1 kg block on the 2 kg block is 14N.
What is then the force exerted by the 2 kg block on the 1kg block? If it is 14N, then shouldn't the 2kg block stay in...
Homework Statement
Three boxes, A, B, C, are positioned next to each other on a friction-less surface, an applied force acting on box A causes all the boxes to accelerate at 1.5 m/s/s. Calculate the force exerted by box C on box B. ma= 8 kg mb=10 kg mc= 5 kg
Homework Equations
Fnet=MA
The...
Three High energy Photons spontaneously convert into electron positron pairs, The electron on the left marked A is created and and destroyed within a short interval, sending an electric field burst towards electron B shortly after it's created, just enough so that Electrons B's electric field...
To every action, there is an opposite and equal reaction. This is Newton's third law. What is the opposite reaction of the conversion of kinetic energy to momentum. Don't say stasis because motion is greatly linked to time. If time freezes, it isn't the opposite of it moving forward bot. Ore it...
If you fill a balloon with air and let it go, since the initial momentum was 0 and the air in the balloon is pushed in one direction, the balloon must move in the other direction. What is the cause of the force that causes the balloon to move this way?
I need some help understanding how Newton's third law applies to field forces (namely gravitation).
The third law in contact forces seems straightforward to me. Billiard ball A, which is moving, hits billiard ball B. The collision exerts a force on Ball B, resulting in its acceleration...
Homework Statement [/B]Find the normal force exerted on a 68.2 kg blacksmith's anvil by the level block of wood that is supporting it.Homework Equations [/B]f=ma Ff=uFnThe Attempt at a Solution [/B]I have tried to find all the forces acting on the anvil while using its mass but I am not...
Hello!
I'm a high school teacher in physics. I will teach Newtons third law this coming week and found the following question (regarding a horse pulling a carriage):
"If the force on the carriage is equal and opposite to the force on the horse how can the horse pull the carriage? Is the...
dear sir,
we know that third law of motion says that every action has a equal and opposite reaction. quantum mechanics tells us that it is possible not predict the position as well as the speed of electron. i like to know if electrons ,protons and neutrons form a system called atom...
Homework Statement
A 2000kg car pushes a 1000kg garbage can at constant speed . The car exerts a force of magnitude CB on the garbage can, and the garbage can exerts a force BC on the car. Which force has greater magnitude, or are they equal? explain
Homework Equations
Fcb=-Fbc
The...
Homework Statement
two hockey players are standing on ice. Player A is 100kg and player B is 112kg, Player A pushes B with 40N and player B pushes A with 50N.
what are the action/reaction forces?
what are the accelerations?Homework Equations
F = maThe Attempt at a Solution
player A has a...
Sometimes I wonder if it actually possible to prove the action-reaction principle. I do know that Newtons laws are empirical but then if you think about the third law it says that in interaction between two bodies they exert equal and opposite forces on each other. Now what happens in the...
Please anybody explain me ... if i punch a soft cushion hardly say "F" force will thw cusion hurt me with the same ... every body says "NO" ok all right everybody says "you, in this case have not applied the "F" force because most part of it is wasted in changing the shape of cusion " so here...
Homework Statement
An elevator containing 3 passengers(with a mass of 72kg 84 kg and 35 kg) has a mass combined of 1030 kg . The cable attached to the elevator exherts an upward force of 12000 N. But the friction opposing the motion of the elevator is 1400 N.
a) Draw a free body diagram...
Whats more basic - Newtons third law or conservation of momentum
You can prove Newtons third law by conservation of momentum but you can also prove conservation of momentum by Newtons third law. What comes first?
Hi friendz
I m new to this forum
I have a problem in a question which is as follows-
If a body of mass m collides with a body of mass 2m it changes its direction of motion buy when it collides with a body of same mass m it stops and when it collides with a body of mass m/2 it does not change...
Coloumbs law states that the force exerted by two charged particles on each other is given by f = kq1q2/d^2
Now say two charged particles (charge type irrelevant in question) x and y are d metres from each other then y exerts a force f on x. But since x is also exerting f on y then won't it...
Figure shows a block of mass resting on a slope. The block has coefficients of friction and with the surface. It is connected via a massless string over a massless, frictionless pulley to a hanging block of mass 2.0 kg.
i got this first one: What is the minimum mass that will stick and not...
If two objects are stacked in an accelerating elevator what is the force equal and opposite to the normal force on the top object?
I was thinking that it has to be either the force of gravity or contact force between the two objects could it be anything else?
Hello PF members,
I was wondering whether Newtons third law was exclusive to spacecraft thrust; space being empty and without enough particles for a force to push against. That in order to produce thrust in space, you would need to carry the fuel that you plan to eject with you...
When a car is moving, the engine is transferring Chemical Energy to Kinetic Energy. He is doing work against the force of friction. If the force of friction is 210 N and the engine exerts a pull force for 10 M it transferred 2100J of Chemical Energy from its fuel to Kinetic Energy, considering...
Homework Statement
A particle of mass 4kg is being towed at a constant speed up a rough plane inclined at 30 degrees to the horizontal by a force 4g N acting parallel to the slope. At the top of the slope the particle moves onto a rough horizontal slope with the same coefficient of friction...
Homework Statement
A lead block is suspended from your hand by a string. The reaction to the force of gravity on the block is the force exerted by:
(a) the string on the block (b) the block on the string (c) the string on the hand
(d) the hand on the string (e) the block on Earth...
I have been thinking about a bar magnet and an infinite wire in free space. The wire is positioned below the north pole of magnet and carries a current.
1) The force from the magent on the wire: Due to the magnetic field, the Lorentz force on the electrons in the wire creates a force on the...
in Newtons third law of motion every action has equal and opposite reaction so my question is that when block hits another block the blocks exert equal force on another so why they move they had to stop immediately.
Homework Statement
A train consisting of two cars pulled by a locomotive experiences an acceleration of 0.33m/s^2 [fwd]. Friction is negligible. Each car has a mass of 3.1 * 10^4 KG.
a. ) Determine the force exerted by the first car on the second car.
b. ) Determine the force exerted by...
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...
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...
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...
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...
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...
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...
Please help me because my teacher has not explained how to do questions involving angles.
Blocks X and Y of masses mx=5.12kg and my=3.22kg are connected by a fishing line passing over a frictionless pulley. Show that block X slides up the incline (35.7 degrees above the horizontal) with...
Homework Statement
Two blocks are lined up in a row. Block A a mass of 1kg, and Block B with a mass of 2kg. If block a is A is pushed forward by 12N, how much force does Block B exert on Block A. Friction can be nelected.
Homework Equations
Newtons Third law
F(A on B)=-F(B on A)...