Newton's 3rd law and horse cart

  • Context: High School 
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Discussion Overview

The discussion revolves around the application of Newton's 3rd law in the context of a horse pulling a cart. Participants explore the mechanics involved, particularly focusing on the forces at play and the implications of different conditions, such as surface friction.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions how a horse can pull a cart if every action has an equal and opposite reaction.
  • Another participant suggests that the reaction force occurs on a different body, implying that the forces are not directly opposing in the context of the horse and cart system.
  • A third participant explains that at steady speed, the horse pushes on the ground, which in turn pushes forward on the horse, while the cart pushes backward on the ground with a force equal to that exerted by the ground on the horse, leading to tension in the connection between horse and cart.
  • A fourth participant introduces a hypothetical scenario where the horse and cart are on a very slippery surface, suggesting that without traction, the horse would be unable to pull the cart, raising questions about the role of friction in this interaction.

Areas of Agreement / Disagreement

Participants express different viewpoints regarding the mechanics of the horse-cart system, and while some explanations are provided, there is no consensus on the implications of the slippery surface scenario or the overall understanding of the forces involved.

Contextual Notes

The discussion does not resolve the implications of the different scenarios presented, particularly regarding the role of friction and the conditions under which the horse can effectively pull the cart.

vinodjacob
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If every action has an equal & opposite reaction, how can a horse pull a cart forward ?
 
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because the reaction is on a different body
 
Assuming a steady speed, there's no reactive (related to acceleration) force. The horse pushes on the ground which pushes forwards on the horse. The cart pushes on the ground with pushes backwards with a force equal to the forwarce generated by the ground on the horse. There's a tension equal to this force between the connection from horse to cart. The tension pulls back on the horse and forwards on the cart.
 
Here's something to think about. If the horse and cart were on very, very slippery ice and the horse had no horse shoes, he could not pull the cart forward. What does that suggest?
 

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