Pushing a cart, using Newton's Third Law

[Libohove90]

I am trying to fully understand Newton's Third Law. I am getting there, but there are a few examples that sort of have me scratching my head for a bit.

Me and a cart are stationary, then I decide to push the cart. I exert a force on the cart and simultaneously, the cart exerts an equal and opposite force on me.

If this occurred in space, the cart and I would have went in opposite directions after the push (conservation of momentum), but on the Earth, this is not apparent. I realize the friction of the floor has a role here. Why is it that both the cart and I accelerate in the same direction as I push it?

Can someone clear this up a bit for me? I would gratefully appreciate informative replies :)

 

[willem2]

I am trying to fully understand Newton's Third Law. I am getting there, but there are a few examples that sort of have me scratching my head for a bit.

Me and a cart are stationary, then I decide to push the cart. I exert a force on the cart and simultaneously, the cart exerts an equal and opposite force on me.

If this occurred in space, the cart and I would have went in opposite directions after the push (conservation of momentum), but on the Earth, this is not apparent. I realize the friction of the floor has a role here. Why is it that both the cart and I accelerate in the same direction as I push it?

Can someone clear this up a bit for me? I would gratefully appreciate informative replies :)

You're not only pushing the cart, you are also pushing the Earth in the opposite direction. Both of them will push back. The Earth is so massive it will hardly move at all, but the cart will move if you push it. To keep contact with the cart you must push the Earth harder, so it will push back harder than the cart, so you will move in the same direction as the cart.

 

[Libohove90]

You're not only pushing the cart, you are also pushing the Earth in the opposite direction. Both of them will push back. The Earth is so massive it will hardly move at all, but the cart will move if you push it. To keep contact with the cart you must push the Earth harder, so it will push back harder than the cart, so you will move in the same direction as the cart.

So the fact that the Earth is pushing me more than the cart is, is what causes me to accelerate in the same direction as the cart?

Why must I push the Earth harder to keep contact with the cart?

 

[willem2]

So the fact that the Earth is pushing me more than the cart is, is what causes me to accelerate in the same direction as the cart?

Why must I push the Earth harder to keep contact with the cart?

If you push the cart and the Earth with the same force, you will stay in one place, because the net force on you is 0. The Earth will stay in the same place because it is so massive, but the cart will accelerate. If you keep pushing it, it will roll beyond the reach of your
arms and you can no longer push it.

 

[sardar]

Newton's Third Law states that for every action, there is an equal and opposite reaction. In the case of pushing a cart, when you exert a force on the cart, the cart exerts an equal and opposite force on you. This can be explained by the concept of forces acting in pairs. When you push on the cart, you are applying a force in one direction, but the cart is also exerting a force on you in the opposite direction. This is due to the fact that the cart has mass and therefore, inertia.

Now, why do both the cart and you accelerate in the same direction? This is because of the presence of friction between the cart and the ground. When you push the cart, the friction between the cart and the ground allows for the cart to move in the same direction as your push, while also exerting a force on you in the opposite direction. This is why you are able to move the cart in the direction you want, despite the fact that the cart is also exerting a force on you in the opposite direction.

However, it is important to note that the friction between the cart and the ground is not always constant. It depends on factors such as the weight of the cart, the surface it is on, and the force you are exerting on the cart. In space, where there is no friction, the cart and you would indeed move in opposite directions after the push, as there would be no external force acting on the cart to keep it moving in the same direction as your push.

I hope this explanation helps to clarify the concept of Newton's Third Law and the role of friction in the motion of the cart and you. Keep in mind that there are many factors at play in any given scenario, and it is important to consider all of them in order to fully understand the situation. Keep exploring and asking questions, as that is the key to understanding complex scientific principles.