# Shared Flashcard Set

## Details

Circular Motion and Equilibrium
Exam 3
31
Physics
11/10/2011

Term
 Define force and torque
Definition
 Force- act necessary to produce linear motionTorque- the act necessary to produce angular motion (or to make an object twist, spin, or rotate)
Term
 State the two conditons of equilibrium
Definition
 Fnet=0τnet=0
Term
 Discuss the physics of circular motion
Definition
 To produce circular motion, an object must be moving at a constant speed on a horizontal surface. It is accelerating because of the change in direction. Also, there must be a net force acting on the object for it to accelerate, and any force can produce circular motion. The acceleration and Fnet are always towards the center of the circle, and there must always be a force to keep the object in circular motion.
Term
 Discuss centripetal and centrifugal forces, including frames of reference
Definition
 Centripetal is a force acting towards the center of the circleCentrifugal is a false force, which acts away from the center of the circleFrames of reference are a set of axes which the position or motion of an object can be described Equilibrium exists in the rotating frame if all forces balance, including an inertial "centrifugal" force
Term
 What must occur for an object to tip over?
Definition
 The objects center of mass must stay inside the axis of rotation
Term
 Why won't a sphere tip over?
Definition
 The center of mass of a sphere is located at its center, and it is always supported at its center when balancing. Its axis of rotation is also at its center, so its center of mass cannot go outside of the axis of rotation
Term
 What will a net torque do to an object? Net force?
Definition
 An object will stay in rotation unless acted upon by an external net torque. If there is a net force acting on a mass, then it must be accelerating.
Term
 Define center of mass.
Definition
 the point at which the entire mass of a body may be considered concentrated
Term
 Torque depends upon...
Definition
 Lever arm (distance from the axis of rotation to the applied force) and Force
Term
 If torque is constant, how are the other two quantities related?
Definition
 F α1/r; inversely proportional
Term
 Why does a mechanic put a pipe extension on a stubborn nut?
Definition
 To increase the lever arm; τ α r, so increasing the lever arm increases the torque and the nut will come off.
Term
 At maximum torque, how are the two quantities related?
Definition
 F is perpendicular to r (torque is at a maximum at 90°
Term
 Why is it difficult to open a jar with wet, soapy hands?
Definition
 If friction is one the force acting to produce the circular motion to open a jar, then wet, soapy hands decreases the coefficient of friction, making it more difficult to open.
Term
 Discuss the physics of a rock being whirled at the end of a string at constant speed.
Definition
 UCM, the acceleration and force act towards the center of the circle. There is always a force keeping the rock in circular motion, once this force stops acting on the rock, it will accelerate linerally.
Term
 State and discuss Kepler's laws of planetary motion.
Definition
 I. Orbit of the planets are elleptical with the sun.II. Equal areas in equal times (the closer a planet is to the sun, the faster its moving) III. The square of a planet's orbital period (T^2) is proportional to its avg distance to the sun cubed (r^3) [T^2 α r^3]Used experiments to discover the laws of nature
Term
 State and discuss Hooke's Law.
Definition
 F=kΔxForce is proportional to displacement
Term
 Who is Tycho Brahe? What did he contribute to astronomy?
Definition
 well known astronomer who was assisted by Kepler. When he died, Kepler used his astronomical results to develop his own theories of astronomy. He observed the planetary motion particularly of mars, and obtained crucial data that Kepler later used.
Term
 What forces can produce circular motion?
Definition
 Any force:-normal-tension-friction-gravitational-centripetal v centrifugal
Term
 Why does jupiter have a period longer than 1 year?
Definition
 Earth is 1 AU from the sun, and a period is one year. Jupiter is almost 5 AU from the sun, so the period is much longer.
Term
 Where is the earth moving faster around the sun, January or July?
Definition
 January, because it is closer to the sun. Kepler's second law, equal areas equal times, says that when a planet is closer to the sun it is moving faster.
Term
 How does a tight rope walker stay on the wire?
Definition
 Balancing center of gravity, keeping their center of mass withing their axis of rotation
Term
 Define linear velocity
Definition
 V=Vo-at; how fast an object accelerates linearly
Term
 Define angular velocity
Definition
 ω=ωo-αt; how fast an object is rotating (accelerating angularly)
Term
Definition
 10 rev/min (2
Term
 How are v and ω related mathematically?
Definition
 v=Rω; v is proportional to ω
Term
 Discuss τnet=Iα
Definition
 I is the moment of intertia (resistance to an objects change in angular velocity) This equation means that an object will stay in rotation unless acted upon by an external net torque.
Term
 Define I, moment of inertia
Definition
 Resistance to an objects change in angular velocity
Term
 Write Newton's laws using τnet
Definition
Term
 Define geosynchronous orbit. How far from earth's surface is a satellite in geosynchronous orbit?
Definition
Term
 Can a yo-yo be whirled fast enough to be completely horizontal?
Definition
Term
 Use the gravitational force to determine g as a function of distance from the center of earth. Is g constant?
Definition
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