Ch 4 Tension

The physics Classroom Equilibrium and Tension


When solving tension problems, it is important to think in terms of vectors and their x and y components. Remember Fnet = ZERO!
DRAW a picture of the vectors and the direction they point. Be sure to note the angles and fill in the missing angles in a triangle using the given info.

With Symmetry

Without Symmetry

How to solve tension problems

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In both of the cases shown above, the sum of the forces in x and the sum in y both equal zero.
The two values of y that point up are equal in magnitude to the force pointing straight down.
The force in x pointing to the right is equal in magnitude, but opposite in direction as the force in x that
points to the left.

CAUTION- set up your triangles, label the angles, and carefully use sine and cosine to find the x and y components.
Be sure to base you use of sine and cosine on the triangles you have drawn and the angles as you label them!
Do not simply assume that you will use cosine for x and sine for y. You might, but its just as likely as you won't.
It all depends on how you have constructed the triangles and placed the angles.

With Symmetry

The two y direction forces will each carry half of the downward pointing weight. This will be key to solving these
types of symmetrical problems.

Without Symmetry

Usually you will need to solve these problems using substitution. remember that the two x components will be equal in
value and that fact is likely to be the key to success with substitution. You can use your two equations with two unknowns to
solve for one value and then back substitute.