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Physics Lesson 6.4.3 - What happens if more than two forces are acting on a turning system?
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Welcome to our Physics lesson on What happens if more than two forces are acting on a turning system?, this is the third lesson of our suite of physics lessons covering the topic of Moment of Force. Conditions of Equilibrium, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
What happens if more than two forces are acting on a turning system?
If there are more than two forces acting on such a system, first we determine the direction of rotation of each force. This is because they may be on the same side of the bar but act in opposite directions as shown in the figure.
From the figure, you can see that F1 causes an anticlockwise turning effect in the system while F2 causes a clockwise effect despite both forces act due right of the turning point. On the other hand, F3 causes a clockwise effect. Therefore, if the system is in equilibrium, we must write (in scalar mode):
instead of
Therefore, we must solely consider the direction of rotation and not the direction in which a force acts in respect to the turning point.
Example 3
Three forces are acting at the system shown in the figure below.
Solution 3
F1 turns the system anticlockwise while F2 and F3 clockwise. Also, d2 = 60 cm = 0.6 m and d3 = 80 cm = 0.8 m.
If there is equilibrium, we have:
Or
All forces are normal to the bar, so, no change is needed on them. Substituting the known values, we obtain
30 = 26 + F3 × 0.8
30-26 = F3 × 0.8
4 = F3 × 0.8
F3 = 4/0.8
F3 = 5N
You have reached the end of Physics lesson 6.4.3 What happens if more than two forces are acting on a turning system?. There are 7 lessons in this physics tutorial covering Moment of Force. Conditions of Equilibrium, you can access all the lessons from this tutorial below.
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