6.6 Equilibrium Rules Flashcards
When two objects interact, they always exert…
… equal and opposite forces on one another
What does a free body force diagram show
Only the forces acting on the object
For a point ;object acted on by three objects to be in equilibrium
F1 + F2 + F3 = 0
They must give an overall resultant force of zero
How can you find an unknown force or angle - scale diagram
Draw one of the known force vectors F1 to scale
Use a protractor and ruler to raw the other known force at the correct angle to F1
The third side can then be drawn in to give the unknown force
How can you find an unknown force or angle - calculation
By resolving it and F2 parallel and perpendicular to the base force F1
Label θ2 as the angle opposite F2 and θ3 as the angle opposite F3, the perpendicular components of the resolved forces F2sinθ3 and Fsinθ2 correspond to the height of the triangle and are equal and opposite to each other
Motion of an object in equilibrium
At rest or moving with a constant velocity
The forces acting on it must give zero resultant and their turning effects must balance out as well
For a body in equilibrium:
The resultant force must be zero, if there are only three forces, they must form a closed triangle
The principle of moments must apply (ie. the moments of the forces about the same point must balance out)
