Newton's third law Definition and 252 Threads

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...

So, I know that there is a Normal force exerted on the book by the table, and, according to Newton's Third Law, the book exerts a force onto the table. However, I have two questions: if I were to push down on the book, would that Normal force increase? What "creates" the Normal force? Is it the...

Homework Statement Newton's third law of motion is often summarised as 'Every action (force) has an equal and opposite reaction'. A book rests on a table. If the weight of the book is the 'action' force, what is the 'reaction' force? A the pull of the book on the Earth B the pull of...

Homework Statement A small mass (1 kg) sits next to a larger mass (3 kg) on a table. A force of 5 Newtons pushes from left to right on the system while a force of 3 Newtons pushes from right to left on the system. Am I justified to conclude that the net force on the larger block has magnitude...

Homework Statement Homework Equations principle of moments Newton's 3rd law The Attempt at a Solution Okay. I am not asking how to solve this question. I just have a little misunderstanding of the concept of the Newton's Third Law. I will get straight to the point. For example, in this...

when a stone is dropped in a beaker containing water,it sinks.But according to Newton's third law of motion the water should also exert an equal force upwards...so the stone should float. This violating the third law but why?

Hello, I am returning to college after a ten year hiatus and am taking an online course on edx to try and refresh my knowledge a bit before the fall. I read a few other posts on Newton's Third law, but it seems I am falling short on this one concept. In the case of an object, m_1, which is at...

Newton's Third Law concerns the forces of interaction between two bodies. Which of the following statements relating to the third law is not correct ? A. The two forces must be of same type B. The two forces must act on different bodies. C. The two forces are always opposite in direction D. The...

How did Newton predict his third law? If we take the system as the whole universe Newton's third law leads that the net force of the system is zero.Did Newton have an insight about this?

Do weight and normal contact force always act in equal and opposite directions?

I took a practice Ap Physics test today and did well, but there was a basic problem that hung me up: there are two boxes on the ground on top of each other. the top box's mass is 2m, and the bottom's is 1m. question: just looking at the bottoms box's normal force, does it equal the 2m box on...

I need to think of all the physics principles to explain how one can stack spherical items (ex. baseballs) on top of each other. So far I've thought of one. 1. Newton's third law In this case, the reaction is the normal force in each baseball that is stacked and the action is the force of...

Homework Statement A 91-kg astronaut floats outside a 3,131 kg spacecraft . She's initially stationary with respect to the spacecraft . Then she pushes against the spacecraft , and moves away at 0.195 m/s to the left. Find the SPEED of the recoiling spacecraft . Homework Equations Force =...

So a truck hits a car, which is at rest. Would there be a moment in time when a car stops exerting a force in equal magnitude but in opposite direction (Newton's third law)? To put in some arbitrarily numbers to make the example easier to understand. Truck weighs 1000 kg, and the car weighs...

I am the kind of guy that always needs to return to the horse-and-carriage problem to hone in my understanding of Newton's Third Law. Here's my question. Assume a rocket in space is applying a force to another object of equal mass in space. Now, I understand the object in space is experiencing...

Homework Statement I am stuck on this problem: So the question is asking for F21, F12, F32, and F23. (That's the force by 2 on 1). The mass of m2 is variable. There are four cases where I need to solve for the forces: when m2 has mass of 3kg, 0.3kg, 0.03kg, and 0kg. The mass of m1 = 2.5kg, the...

Homework Statement Consider Newton’s force law for two particles interact through a central force F12(r1',r2',u1,u2), where by Newton’s third law F12 = -F21. m1(d^2r1/dt^2) = F12(r1,r2,u1,u2) m2(d^2r2/dt^2) = F21(r1,r2,u1,u2) A. Show that Newtonian mechanics is form invariant with respect...

Homework Statement Consider Newton’s force law for two particles interact through a central force F12(r1',r2',u1,u2), where by Newton’s third law F12 = -F21. m1(d^2r1/dt^2) = F12(r1,r2,u1,u2) m2(d^2r2/dt^2) = F21(r1,r2,u1,u2) A. Show that Newtonian mechanics is form invariant with respect to...

Please forgive me for my naiveté but I've got to resolve a conceptual problem I'm having. If every action has an equal and opposite reaction then why don't all the forces in the universe cancel each other out. For example if i am in space and I hit a ball with force X then the ball reacts back...

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...

Got it!

Homework Statement . question is as attached. answer is 2f/5..how do u get this? Homework Equations F=ma F= (5m)a a= F/(5m) The Attempt at a Solution gotten a=F/5m , but why the answer is 2f/5?

When a horse pulls tonga, the Tonga exerts an equal force on Tonga then why does it move. How is Newton's third law applied to such case.

NOTE: The following questions are not part of any homework assigned. This is part of finding extra concept-related questions to help me study for my physics unit test. Homework Statement I have conceptual questions, not problems. I'll provide sufficient evidence that I've attempted to think...

Hi, I am facing some issues while dwelling upon the application of Newton's third law of motion to the famous "Horse-Cart" Problem.Anybody who is clueless about what I am talking about please follow the link: https://www.lhup.edu/~dsimanek/physics/horsecart.htm As one can see the whole...

Is the force of attraction between an electron and a proton in a hydrogen atom a example of action and reaction to which Newton's 3rd law applies?

If I jump, I accelerate away from Earth. However, if I drop a human on the ground, he doesn't accelerate away from the Earth. In both cases the force used on the Earth is about the same, but acceleration away from the Earth exists in one case and doesn't exist in another case. Why so? (not a...

According to Newton's third law, every force has an equal and opposite reaction force. Which force is equal and opposite to both friction and tension?

1. If Big Bang really happened, then what are the action and reaction forces acting? 2. A quantity like Entropy is always increasing. If average temperature is made constant then universe is getting heated continuously..then what is that being cooled? 3. Total of action and reaction force =0, if...

1. no matter how strong a car engine is a car cannot accelerate on an icy surface 2. A vehicle pushes a car of lesser mass from rest, causing the car to accelerate on rough dirt.

Homework Statement A spring system consists of two parallel springs on top and a single spring connected to them on the bottom as shown: http://i.imgur.com/hgMr12U.png If the system is extended by 7 cm (i.e. x = 0.07m), F = 5N and k2 = 10 N/m, explain why the value of k1 is unrealistic...

Hi, I am a little confused with the concept of action reaction pair of forces. Does this depend on mass? For example, if a train engine is pulling a buggy with force F, what would be the force applied by the buggy on the engine? The masses of the two are different and there is force of...

Newton's third law states that for every action, there is an equal and opposite reaction. This doesn't make sense to me, because it seems as though everything would cancel out and so nothing would ever happen. For example, imagine a person attempting to push a large box; not just a quick push...

Why forces acts on two different bodies with same magnitude and opposite in direction doesn't cancel each other?

After being through with Newton's 3rd law of action reaction pairs, there arise a doubt regarding the categorization of force couple (related to torque) of being or NOT being an example of action reaction pairs.

So I've recently read Newton's third law violates the principles of relativity. I only know how to prove conservation of momentum if Newton's third law holds. I was hoping someone could explain to me this (proving conservation of momentum when Newton's third law is false) without using extremely...

For some reason I couldn't answer this, and I hope you can help me: a) Two people pull on a rope, one with 200 N , the other 100 N. Why is the tension on the rope the shared magnitude of both forces? b) If two people pull on a rope with equal force (say, 100 N), each person pulling feels...

I have always been under the impression that Newton's third law and the law of conservation of linear momentum are really the same thing; synonymous, so to speak. But then I was wondering if Newton's Third Law holds for a non-isolated system. I mean, I know for sure that momentum conservation is...

Newton's third law confusion? If A exerts some force on B then it experiences a force of same magnitude and in opposite direction. This didn't seem intuitive to me so I thought of it this way, Let A and B be a single system. Now there is no net external force acting on the system so the...

Newton's Third Law states that for every action force, there is a reaction force. So take a classical problem with a basketball player. The Earth has a gravitational force on the player, and thus player exerts an equal and opposite force on the earth. The player is stationary. My first...

Homework Statement A chain of three links, each with a mass 0.2 kg, is being pulled up by a person lifting the top link with 8.88 N of force and the chain accelerates upward. Calculate three forces that are acting on the middle link while the chain is accelerating. Homework Equations ƩF = ma...

Homework Statement Two hockey players are standing stationary on the ice facing one another. Player A has a mass of 85kg and Player B is 110kg. They shove each other and player A ends up with a velocity of 1.5m/s [W]. Find the final velocity of Player B. Solution Fa=Maaa Fa=(85)(1.5-0/t)...

"For every action there is an equal and opposite reaction." I'm having a difficult time wrapping my head around this. I'm having a hard time applying it to certain situations. For example, a hammer hitting a nail, but more presently a problem in my homework. A building is being torn down...

Homework Statement A paintball with a mass of 0.15 kg is fired from a paintball gun that has a mass of 5.5kg. The paintball leaves the gun with a velocity of 45 m/s [N] having accelerated for 0.10s. Calculate the acceleration and the final velocity of the paintball gun.

I have a question for which I am intensely confused. Lets say a car was pushing a big truck from behind. And the car (and truck) are accelerating, then there is a breakdown because the car applies all the force it has to the truck, which pushes back with equal force. So the car shouldn't be...

Hello, I have seen several explanations on the Internet about how to resolve Newton's Third Law and Unbalanced Forces, but none made sense to me in a way that I really understood it. Scenario 1: There is a block on the ground, the ground has friction with say static friction force 10 N...

If Newtons third law says there is an equal and opposite reaction how can there be energy transfer. For example if I push a box and give it 1000 joules of energy wouldn't it "give back" the energy. Also does an object have to be moved for it to gain energy, if I were to punch a book many times...

Sorry guys not a physicist!Only wish to know if there is agreement between Newton laws of motion and SR/GR in particular?I know these two don't match in some cases? What are they in simple words please!? Cheers

There seems to be a problem with radiation reaction force. Let's look at charged sphere, attached on a rod to an object with larger mass, and rotating around its centre together with it. The rotating charged sphere emits radiation with power P. The sphere's speed is V. Assuming energy is...

I have a quick question on Newton's third law. When a 100kg astronaut in space is holding a 100 kg rock and then pushes it away from him with 50 joules of energy (the kinetic energy put into the system) and a second astronaut (observer) is watching, sitting still relatively to the location...