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Ch. 12 - Static Equilibrium; Elasticity and Fracture
Giancoli Douglas - Physics for Scientists and Engineers 5th edition
Giancoli Douglas5th editionPhysics for Scientists and EngineersISBN: 9780137488179Non è quello che usi tu?Cambia libro di testo
Capitolo 12, Problema 64a

A pole projects horizontally from the front wall of a shop. A 6.1-kg sign hangs from the pole at a point 2.2 m from the wall (Fig. 12–88). What is the torque due to this sign calculated about the point where the pole meets the wall?
A horizontal pole extends from a wall, supporting a 6.1-kg sign hanging 2.2 m away from the wall.

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Identify the formula for torque: Torque (τ) is calculated using the equation τ = r × F × sin(θ), where r is the distance from the pivot point to the point of force application, F is the force, and θ is the angle between the force and the lever arm.
Determine the force acting on the sign: The force is due to the weight of the sign, which is given by F = m × g, where m is the mass of the sign (6.1 kg) and g is the acceleration due to gravity (approximately 9.8 m/s²).
Substitute the values into the torque formula: The distance r is given as 2.2 m, and the angle θ is 90° because the weight acts vertically downward, perpendicular to the horizontal pole. Since sin(90°) = 1, the torque simplifies to τ = r × F.
Combine the expressions: Replace F with m × g in the torque formula, resulting in τ = r × m × g. Substitute the known values for r (2.2 m), m (6.1 kg), and g (9.8 m/s²) into this equation.
Perform the multiplication to find the torque: Multiply the values of r, m, and g to calculate the torque about the point where the pole meets the wall. Ensure the units are consistent, and the result will be in Newton-meters (N·m).

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Torque

Torque is a measure of the rotational force applied to an object around a pivot point. It is calculated as the product of the force applied and the distance from the pivot point to the line of action of the force, often expressed in the formula τ = r × F, where τ is torque, r is the distance, and F is the force. In this scenario, the weight of the sign creates a downward force that generates torque about the point where the pole meets the wall.
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Net Torque & Sign of Torque

Center of Mass

The center of mass is the point in an object where its mass is evenly distributed in all directions. For a uniform object, like the sign, the center of mass is typically at its geometric center. Understanding the location of the center of mass is crucial for calculating the torque, as the force of gravity acts through this point, affecting the torque produced about the pivot.
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Intro to Center of Mass

Equilibrium

Equilibrium refers to a state where the sum of forces and the sum of torques acting on an object are zero, resulting in no net movement. In this problem, analyzing the torque due to the sign helps determine if the pole can support the sign without tipping or rotating. If the torque from the sign exceeds the counteracting torque from the pole's support, the system will not be in equilibrium.
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