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I am trying to construct the free body diagram of a mass suspended by two vertical springs such

sd

I concluded that the weight of the mass exerts a force on the upper spring causing a tension force to arise in the upper spring, and the weight of the mass exerts a force on the lower spring causing it to compress producing a thrust force.

Hence my diagram is as shown

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However the textbook I am using instead shows the forces exerted by the springs acting in opposite directions,

sf

I do not understand, why would the lower spring exert a tension force instead of a thrust force?

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It actually doesn’t matter. You can make either assumption and simply do the math to find the value of the force. If you get a negative number then you know your original guess was wrong, and if you get a positive number then you know your original guess was right. Either way works. Just guess one, and be consistent from that point on.

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