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Ch 08: Dynamics II: Motion in a Plane
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Not the one you use?Change textbook
Chapter 8, Problem 12

It is proposed that future space stations create an artificial gravity by rotating. Suppose a space station is constructed as a 1000-m-diameter cylinder that rotates about its axis. The inside surface is the deck of the space station. What rotation period will provide 'normal' gravity?

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Understand the problem: The goal is to determine the rotation period of a cylindrical space station that provides artificial gravity equivalent to Earth's gravity (normal gravity, g = 9.8 m/s²) on its inside surface. The artificial gravity is created by the centripetal force due to the rotation.
Identify the relationship between centripetal acceleration and gravity: The centripetal acceleration (a_c) experienced by an object on the inside surface of the rotating cylinder must equal Earth's gravitational acceleration (g). The formula for centripetal acceleration is: a=ω2r, where ω is the angular velocity and r is the radius of the cylinder.
Determine the radius of the cylinder: The diameter of the cylinder is given as 1000 m, so the radius is half of the diameter: r=1000/2=500m.
Relate angular velocity to the rotation period: The angular velocity (ω) is related to the rotation period (T) by the formula: ω=2π/T. Substitute this into the centripetal acceleration formula: a=(2π/T)2r.
Solve for the rotation period (T): Set the centripetal acceleration equal to Earth's gravity: (2π/T)2r=g. Rearrange the equation to isolate T: T=2π/g/r. Substitute the values for g and r to find the rotation period.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Centripetal Acceleration

Centripetal acceleration is the acceleration directed towards the center of a circular path that keeps an object moving in that path. It is essential for understanding how artificial gravity can be created in a rotating space station. The formula for centripetal acceleration is a = v²/r, where v is the tangential velocity and r is the radius of the circular path.
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Gravitational Force

Gravitational force is the attractive force between two masses, which on Earth gives us a standard acceleration of approximately 9.81 m/s², referred to as 'normal' gravity. In the context of the rotating space station, the centripetal acceleration must equal this gravitational force to simulate Earth-like conditions for the occupants.
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Rotational Dynamics

Rotational dynamics involves the study of the motion of objects that are rotating. It includes concepts such as angular velocity and torque. For the space station, the rotation period (the time it takes to complete one full rotation) is crucial, as it determines the angular velocity needed to achieve the desired centripetal acceleration that mimics normal gravity.
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Related Practice
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Three satellites orbit a planet of radius R, as shown in FIGUREEX13.24. Satellites S₁ and S₃ have mass m. Satellite S₂ has mass 2m. Satellite S₁ orbits in 250 minutes and the force on S₁ is 10,000 N.(b) What are the forces of S₂ and S₃?

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A 200 g block on a 50-cm-long string swings in a circle on a horizontal, frictionless table at 75 rpm. What is the tension in the string?

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Communications satellites are placed in circular orbits where they stay directly over a fixed point on the equator as the Earth rotates. These are called geosynchronous orbits. The altitude of a geosynchronous orbit is 3.58 x 107 m (approximately 22,00 miles). Astronomical data are inside the back cover of the book. Find the value of g at this altitude.

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Suppose the moon were held in its orbit not by gravity but by a massless cable attached to the center of the earth. What would be the tension in the cable? Use the table of astronomical data inside the back cover of the book.

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A satellite orbiting the moon very near the surface has a period of 110 min. What is free-fall acceleration on the surface of the moon? Astronomical data are inside the back cover of the book.

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A 5.0 g coin is placed 15 cm from the center of a turntable. The coin has static and kinetic coefficients of friction with the turntable surface of μs = 0.80 and μk = 0.50. The turntable very slowly speeds up to 60 rpm. Does the coin slide off?

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