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Logs dropped upright into a pond do not remain upright, but float "flat" in the water. Explain.

Logs dropped upright into a pond do not remain upright, but float "flat" in the water. Explain.

Grade:11

2 Answers

Kevin Nash
askIITians Faculty 332 Points
8 years ago
When a log is dropped upright in a water, the buoyant exerted by the water acts on the log at its center of buoyancy (B). The weight (W) of the log acts downward towards the center of gravity (G). In this case, the center of buoyant force (Fb) and its center of gravity do not lie on the same vertical line. Thus, a net torque acts on the log which makes the log unstable.
This is shown below:
234-1370_1.PNG
For equilibrium position, the center of buoyancy and the center of gravity should act on the same vertical axis of the log. This happens when the log float flat in the water. It is shown below:
234-2088_1.PNG
Thus, the log dropped upright in the pond experiences a net torque and experiences an unstable equilibrium. It will tend to remain in the stable equilibrium and achieved by floating flat in the pond. Therefore, logs dropped upright into a pond do not remain upright, but float flat in the water.
grenade
2061 Points
8 years ago
torque balance

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