username2982648
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#1
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If a 2400kg truck is attached to a Mkg trailer by a tow bar, does the tension in the tow bar act towards the truck or the trailer?

britishtf2 Kyx @OtherPeopleWhoUnderstandMathsAndPhysics
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old_engineer
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#2
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Both ways.

Assuming the truck is towing rather than pushing, it exerts a force on the tow-bar in the direction of motion. The tow-bar exerts an equal and opposite force on the truck (Newton's third law of motion). The tow-bar then exerts the same force on the trailer in the direction of motion, and the trailer exerts an equal and opposite force on the tow-bar.
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britishtf2
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(Original post by LeCroissant)
If a 2400kg truck is attached to a Mkg trailer by a tow bar, does the tension in the tow bar act towards the truck or the trailer?

britishtf2 Kyx @OtherPeopleWhoUnderstandMathsAndPhysics
Tension is always in both directions in the rope/rod/whatever. One way acts on one particle/object, the other acts on the other.
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username2982648
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(Original post by britishtf2)
Tension is always in both directions in the rope/rod/whatever. One way acts on one particle/object, the other acts on the other.
But then surely the tension acting in both directions would cancel each other out?
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ShadowSeeker
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(Original post by LeCroissant)
But then surely the tension acting in both directions would cancel each other out?
but we take as one way (one direction)
but in real yes they do cancel as they are opposite ways
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Notnek
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(Original post by LeCroissant)
But then surely the tension acting in both directions would cancel each other out?
One of the tensions is a force acting on the truck and the other is a force acting on the trailer. These forces are acting on different objects so don't "cancel each other out".

Only forces acting on the same object can cancel each other out and cause equilibrium. This is why in force diagrams it's often a good idea to draw separate diagrams if you want to show the forces acting on different objects.
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britishtf2
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(Original post by LeCroissant)
But then surely the tension acting in both directions would cancel each other out?
Each tension only acts on one of the objects, and they act on different objects. This means that each object feels the force of only one of the tensions, so, in the frame of the objects, there is a resultant force acting on them. If the tensions weren't to cancel out OVERALL, the string would stretch*. This is why you have to have to assume that the string/rod is rigid*.

*I believe - please correct me if wrong.
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