A uniform 4-meter board weighing 20 kg rests on two supports: one at the left end and one at the 3-meter mark. A 30 kg child stands at the far right end (4 m).
What force does the LEFT support exert?
The left support barely does any work! The child is so far right that most of the load falls on the right support.
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Place weights on the beam and watch the support forces adjust. Can you make the left support push DOWN?
ΣF = 0 and Στ = 0
Two conditions, not one! Forces balanced doesn't mean torques balanced.
Engineers calculate support forces at each pier using equilibrium — it's all torque balance
A crane arm must balance its load torque with a counterweight — or it tips
Wall brackets must support both the weight AND the torque from the shelf's load
“Equilibrium isn't just about forces — it's about WHERE those forces act.”
Balance Builder
Place weights anywhere on a beam with two supports. Watch forces and torques balance (or not!).
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Can you place a weight so far past the right support that the LEFT support must push DOWN to keep the beam from rotating? That's when the left force becomes negative!
Taking torques about a support point lets you instantly solve for the other support. This is the master technique for all statics problems.