About Newton's IIIrd law horse and cart?

Question

If Newton's IIIrd law is correct, then when a horse pulls a cart, the cart must also pull the horse but this doesn't happens. Why?

Answer 1

if the cart didn't pull the horse, the horse wouldn't feel the cart and could pull whatever charge you wuold dream of. A single horse would then be able to pull several tons at full galop.

so, the answer to your "why?" is : "you're wrong".

Answer 2

The cart definitely pulls back on the horse. Newton's 3rd law deals with interacting objects. The force A exerts on B is equal to and opposite the force B exerts on A. This is always true (whether or not in equilibrium).

Your question should be, "if the cart pulls back on the horse, why do the horse and cart accelerate forward?" There's a simple answer to this: there are other interactions.

In this case, the horse pushes back on the ground, and the ground pushes forward on the horse (static friction). There are two forces on the horse: the ground pushing forward on the horse and the cart pulling back on the horse. These are the only two relevant forces on the horse. As long as the ground pushes on the horse more than the cart pulls back, the horse will accelerate. This is Newton's 2nd law. The net force on the horse is equal to the mass of the horse times its acceleration. We can only consider forces *on the horse* in relation to accelerations *of the horse*.

There are also only two forces of interest on the cart: the horse pulling it forward and the ground pushing it back (friction again). Again, if the horse-on-cart force is greater than the ground-on-cart force, the cart will accelerate forward.

Answer 3

But it does pull the horse. Why do you think the horse strains, struggles, sweats, etc.?

Actually Newton's 3rd deals with objects in equilibrium. The object is not in equilibrium if the cart is accelerating. Once the horse and buggy are in equilibrium, all of the force exerted by the horse will be utilized to overcome gravity and friction, thereby pulling the buggy at a constant velocity. The horse will feel the pull of the cart (as friction) with an equivalent amount of force that the cart "feels" from the horse.

Answer 4

The horse is attached to the ground. The Earth is doing the "reaction" here, and yes when the horse pulls the cart the earth responds. Since we're talking about conservation of momentum, the movement of the Earth (far more massive than the cart) is negligible.

If the horse could pull the cart on a frictionless surface, then you would get the kind of reaction that you are imagining; i.e. the horse and cart would slide toward each other a distance inversely proportionate to their respective masses.

Answer 5

The cart does pull the horse, that is why the horse feels resistance and must apply a force to move the cart. The horse must apply a force to overcome inertia, according to F=MA. If the cart did not pull back, it would move effortlessly without any force at all.

Answer 6

Campb.. has a point, your example is more apt for a discussion on the 2nd law rather than the 3rd.

In your example, the opposite reaction is not as clear, as the weight of the cart the force of friction are being mitigated by the use of the wheel to help overcome and facilitate the horizontal force exerted by the horse. Get rid of the wheels and the horse would be more apt to feel the opposite reaction of the friction's horizontal force in the opposite direction.

Here's a quite a link to some lessons on the three laws that may help clarify some things.

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/newtlaws/u2l3b.html

Answer 7

It does in a way. When you pull something heavy, you can feel it resisting. It is hard to pull. That resistance is mathematically a pull in the opposite direction.

But that is not the best situation to demonstrate the 3rd law. A better one has you standing still on a skate board and throwing a heavy object. When you do, you will be pushed in the opposite direction.

Answer 8

newtons third regulation does notice to the cart yet newtons 1st regulation is greater major. that (each merchandise in a state of uniform action has a tendency to proceed to be in that state of action except an exterior stress is utilized to it) or for us lay human beings a physique in action has a tendency to continues to be in action until eventually acted on via an exterior stress or a physique at relax has a tendency to stay at relax until eventually acted upon via an exterior stress notice right here in case you're speaking horse and cart. the cart is at relax until eventually the horse pulls it. The third regulation is there yet in an exceedingly finite variety. under is an internet site that explains it greater effective then i ought to. It explains it greater effective with tug of warfare

Answer 9

Catch the horse with your right hand, and the cart with your left, you will feel how each pulls to its side.

Answer 10

It could happen if the horse and cart were going
up a steep hill and the cart then was more than
the horse could pull.