Conservation of Angular Momentum quiz #1 Flashcards
Conservation of Angular Momentum quiz #1
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Under what condition is the angular momentum of an object or system conserved? Angular momentum is conserved when the net external torque acting on the object or system is zero. Explain the principle of conservation of angular momentum and how it applies to rotating systems. The principle of conservation of angular momentum states that if no net external torque acts on a system, its total angular momentum remains constant. This means that changes in moment of inertia (due to mass or radius changes) must be compensated by changes in angular speed so that the product Iω stays constant. What happens to the angular speed of a spinning ice skater when she draws in her outstretched arms? When a spinning ice skater draws in her outstretched arms, her moment of inertia decreases, so her angular speed increases to conserve angular momentum. How do planets orbiting the sun and skaters doing a spin both demonstrate conservation of angular momentum? Both planets orbiting the sun and skaters spinning conserve angular momentum because, in the absence of external torques, any change in their moment of inertia (such as a skater pulling in arms or a planet moving closer to the sun) results in a compensating change in angular speed so that their angular momentum remains constant. Describe the conditions under which the angular momentum of a system remains constant. The angular momentum of a system remains constant when the sum of all external torques acting on the system is zero. Based on the conservation of angular momentum, how does one expect the planets to spin as their distance from the sun changes? If a planet's distance from the sun decreases (its orbital radius decreases) and no external torque acts, its angular speed increases to conserve angular momentum. An ice skater is spinning with her arms out and is not being acted upon by an external torque. What happens to her angular momentum and angular speed if she pulls her arms in? Her angular momentum remains constant because there is no external torque. As she pulls her arms in, her moment of inertia decreases, so her angular speed increases to conserve angular momentum. How does shortening the radius of rotation affect the angular speed of an object spinning on a string? Shortening the radius of rotation causes the angular speed to increase. This is because the moment of inertia decreases, so angular speed must increase to conserve angular momentum. What happens to the angular speed of a spinning disk when a person lands on it? The angular speed of the disk decreases when a person lands on it. This is due to the increase in total mass, which increases the moment of inertia and requires a decrease in angular speed to conserve angular momentum. If a star collapses and loses half its mass and half its radius, how does its angular speed change? The star's angular speed increases by a factor of 8 after collapsing. This is because both the mass and the squared radius decrease, causing the moment of inertia to decrease and the angular speed to increase to maintain constant angular momentum.