if action is always equal to the reaction, explain how a horse can pull a cart.?

Answer 1

Break down the actions and reactions:

The horse pulls against the cart -- > The cart pulls against the horse

The horse's hooves push against the ground --> The ground pushes against the horse's hooves

So long as the force that the horse applies to the ground as it pushes itself is > the force of friction against the cart, the cart moves.

Answer 2

Even though a complete answer to the Horse and Wagon Question can get rather involved, a clear explanation only hinges on a couple of simple points:

An object accelerates (or not) because of the forces that push or pull on it. (Newton's 2nd Law)

Only the forces that act on an object can cancel. Forces that act on different objects don't cancel - after all, they affect the motion of different objects!

horse pulls wagon" and "wagon pulls horse". They are equal in magnitude and opposite in direction

"horse pushes ground" and "ground pushes horse". They are also equal in magnitude and opposite in direction

so why does the cart accelerate: Newton's 2nd Law says that an object accelerates if there is a net (unbalanced) force on it. Looking at the wagon in the diagram above, you can see that there is just one force exerted on the wagon - the force that the horse exerts on it. The wagon accelerates because the horse pulls on it! The amount of acceleration equals the net force on the wagon divided by its mass (Newton's Second Law).

why horse accelerates: There are 2 forces that push or pull on the horse in the diagram above. The wagon pulls the horse backwards, and the ground pushes the horse forward. The net force is determined by the relative sizes of these two forces.
If the ground pushes harder on the horse than the wagon pulls, there is a net force in the forward direction, and the horse accelerates forward.

Why does the ground push on the horse, anyway? :
The force "ground pushes horse" is the Newton's Third Law reaction force to "horse pushes ground". These 2 forces are exactly the same size. If the horse wants the ground to push him forward, he just needs to push backwards on the ground.
These two forces do not cancel because they act on different objects. The force "ground pushes horse" tends to accelerate the horse, and the force "horse pushes ground" tends to accelerate the ground

What about the ground?
Looking at the force diagram at the top of the page, you see that there is one horizontal force pushing on the ground - the horse pushes on the ground. Therefore, there is an net force on the ground, so the ground should accelerate. Does it?
Of course it does! However the amount of acceleration equals the size of the net force divided by the mass of the Earth - and the mass of the earth is about 6 x 1024 kg. This means that the acceleration of the ground is much, much too small to notice


So, it is possible for horses to pull wagons! It is true that the force that the horse exerts on the wagon is the same size as the force that the wagon exerts on the horse, but these forces do not combine to produce a zero net force. The force exerted on the wagon (by the horse) affects the motion the wagon, and the force exerted on the horse affects the motion of the horse.

Answer 3

Students always get confused about this when they study Newton's 3rd Law. N3 is not a balance of forces, it's a symmetry of forces. Body A pushes body B. Body B pushes body A. Those forces are always the same.
Think of a tug of war, A vs B. Suppose A is winning. Does that mean that A is pulling on B harder than B is pulling on A? NO! It means that A is pushing ON THE GROUND harder than B is pushing ON THE GROUND.
So in your question, the horse pushes on the ground (and friction pushes back) harder than the cart pushes on the ground (i.e. harder than the force of friction that resists the cart's wheels.)
The forces of horse on cart and cart on horse are always equal. Those other forces, the ones that act on the combined system, are not.

Answer 4

The pressure exerted by the horse legs, the foot pressure to the ground is actually opposite to the direction of the cart.

The direction of actions where the foot is pushing the ground is against the direction of the cart that made the cart move to its direction.

dan

Answer 5

The action is the horse pushing against the ground, the reaction is the ground pushing him forward. Since the cart is attached, it moves in the same direction as the horse.

Answer 6

The horse pulls cart not because of forc that it applies on cart but force that it applies on ground to move.When the horse pushes the earth backwards the earth pushes it forwards.This force moves the horse and as the cart is tied to the horse it also moves.

Answer 7

The force acting within the connection between horse and cart is an internal force. The horse's legs driving against the ground are an external force.

Answer 8

This is a very good question and it shows you don't believe anything blindly because it was said by newton. There is limitation of human language and it is impossible to explain everything in words. To keep things simple, the movement of the cart is one of the components of opposite reaction. Similarly, the forward thrust of rocket is outcome of the opposite reaction of jet pressure excerted on the atmosphere. If you add all the positive and negative forces, the net result will be zero.

Similarly you can ask about acceleration also. If rate of change of velocity is acceleration, then why don't we move as we are always under the influence of the gravitational force?. Acceleration is an integral part of force and there can not be acceleration without force. If there is an imbalance, then to compensate for the imbalance the object has to move in the resultant direction untill it is encountered by another force to stop it.

Always keep in mind that a scientific law is not the ultimate answer to a natural phenomenon. Because nature is connected and doesn't work in isolation. Biology, Physics, Chemistry, Maths and evrything else works in synchronisation with each other. We human beings are part of nature and that's the reason we find it difficult to think in isolation about a particular scientific concept Again, it is just an effort to understand nature and we human beings have very limited capacity to understand and explain everything in words. Newton and Einstein also are human beings and they can not play God. Keep your heart away when you study science and maths.

Answer 9

Since the cart is on wheels, it has little friction. But a horse digs his hooves into the ground, and therefore has a lot a friction.
A horse would have a hard time pulling a cart across a skating rink.

Answer 10

As the horse pushes his hooves against the pavement he is propelled in the opposite direction and from the pressure he exerts and in proportion to the amount of that pressure. The Earth, far more massive than the horse, absorbs the energy and does not move in any measureable amount, but the horse certainly moves, bringing the cart along with him.