Question about Newton's Third Law of Motion

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SUMMARY

The discussion centers on Newton's Third Law of Motion, specifically regarding the forces involved when a brick strikes a glass window. According to Newton's Third Law, the magnitude of the force exerted by the brick on the window is equal to the magnitude of the force exerted by the window on the brick, though the effects differ due to the material properties, such as the brittleness of glass. Participants emphasize the importance of considering net forces and the implications of Newton's Second Law, which states that net force is proportional to acceleration.

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  • Familiarity with Newton's Second Law of Motion (f_{net}=ma)
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  • Concept of net force and its components
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jle1092
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A brick hits a glass window. The brick breaks the glass, so:
is the magnitude of the force of the brick, greater, less than, or equal to the magnitude of the force of the window?

Newton's third law of motion states that for every action, there is an equal an opposite reaction.


With this law I think I should say the magnitude is equal, but then again my gut tells me that the law is talking about the net force and this specific question is dealing with this once force itself, so I want to say the magnitude of the force of the brick is greater. What do you think?
 
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magnitudes are equal, direction are opposite, effects are different, effect depends on nature and properties of the material. here, brittleness of glass.
 
Well what I think you should do is think about Newton's second law, which is frequently formulated as:

f_{net}=ma

That is to say, the net force exerted on an object is proportional to its acceleration. Think about the net force acting on the brick, and then break that force down into its components; the normal reaction of the window on the brick and gravity. (It's equivalent, and more straightforward, if you first consider, for example, a skylight instead of a normal window, the brick being dropped vertically downwards onto it.)

If you still need more hints, let me know.
 
Last edited:

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