# Shared Flashcard Set

## Details

Chapter 8
rotary motion, torque, etc.
44
Physics
12/03/2012

Term
 What is rotary motion?
Definition
 when an object spins on its axis in rotational motion
Term
 What is angular displacement? What is its symbol? What units is it measured in?
Definition
 the change in the angle as an object rotates; theta; revolutions, degrees, radians
Term
 What is the angular displacement of a second hand on a clock in ten minutes?
Definition
 10 revolutions; 2 pi; 3600 degrees
Term
 What is angular velocity? What is the symbol? What units is it measured in?
Definition
 the rate of rotation (rev/sec); omega; change in angular displacemnt/change in time; rev/sec or rad/sec or degrees/sec
Term
 What is the angular velocity in radians of a tops that turns 100 times in 5 seconds?
Definition
Term
 What is tangential speed? How does the tangential speed vary across a rotating disk? How do you convert from angular velocity to tangential velocity?
Definition
 the actual meters/sec it is traveling; as you move outward, the faster you go; V=r(omega) and omega must be in radians
Term
 An object has an angular velocity of 50 radians/sec. At a distance of .5m from the axis of rotation what is the tangential speed?
Definition
 V= (50) (.5) V= 25 m/s
Term
 What is angular acceleration? What is the symbol? What are the units?
Definition
 the rate of change of angular velocity; aplpha=change in angular velocity/change in time; rev/s squared
Term
 What does rpm stand for?
Definition
 revolutions per minute
Term
 An object spinning at 1000 rpm slows to a stop in 10 seconds, what is the angular acceleration?
Definition
 0-1000/10=-100 rpms
Term
 What causes rotation? What is torque?
Definition
 torque; rotational effect caused by parallel forces
Term
 How do you calculate torque?
Definition
 T=Fl
Term
 What is the torque arm?
Definition
 perpendicular length from the pivot point to the force
Term
 What happens to the gorque if the line of the force passes through the pivot point?
Definition
 there is no torque
Term
 How do you calculate torque if the force is an angle to the object?
Definition
 find the components
Term
 What is rotational inertia or the moment of inertia?
Definition
 when an object starts rotating, it wants to keep rotating; rotational inertia = moment of inertia
Term
 What deteremines how much rotational inertia something has?
Definition
 the distribution of the mass; the big wheel has more rotational inertia than a small wheel
Term
 What is the center of gravity (mass)?
Definition
 the point at which you draw your force vector down; where the force of gravity acts
Term
 when will toppling occur?
Definition
 when the center of gravity is not over the base of support
Term
 What are the 3 types of equlibrium?
Definition
 stable, unstable, equilibrium
Term
 What are the two conditions of equlibrium?
Definition
 translational and rotational; translational--Fup=Fdown; rotational--CW torque=CCW torque; both of these conditions must be met in order to be in equlibrium
Term
 review all problems: seesaw, torque, equlibriant, bridge, angular displacement, velocity, acceleration, etc
Definition
Term
 What is the angular displacement of a second hand in 1.5 minutes?
Definition
 1.5 revolutions; 540 degrees; 3 pi radians
Term
 What is the angular displacement of a second hand in five minutes?
Definition
 5 revolutions, 1800 degrees; 10 pi radians
Term
 Which part of the earth's surface has the greatest rotational speed about the earth's axis?
Definition
 all parts
Term
 Which part of the earth's surface has the greatest linear speed relative to the axis?
Definition
 equator
Term
 On a particular merry g round, the horses along the outer rail are located three times farther from the axis of rotation than the horses along the inner rail. If a boy sitting on a horse near the inner rail has a rotation speed of 4 rpm and a tangential pseed of 2 m/s, what will be the rotational speed and tangential speed of his sister who is sitting on a horse along the outer rail?
Definition
 4 rpm--rotational; 6 m/s--linear
Term
 A wirte with 4 light bulbs is twirled ina circle. The bulbs are numbered 1-4, with four being on the outside of the circle and 1 being towards the center. Which of the bulbs have the greatest rotational speed? Which of the bulbs has the greatest tangential speed?
Definition
 they have the same rotational speed; bulb 4 has the greatest tangential speed
Term
 A fan rotating at 200 rpms takes 15 seconds to stop turning when it is turned off, what is the angular acceleration?
Definition
 0-200/15=-13.3 rev/min/sec
Term
 torque is a ____or ____.
Definition
 twist or spin
Term
 What are the charateristics of torque?
Definition
 different from force, causes rotation, produced when a force is applied parallel to another force, measured in meter newtons
Term
 What is a pivot point?
Definition
 point of rotation
Term
 What is the torque arm?
Definition
 perpendicular distance from F to pivot point
Term
 What when force is applied further from pivot point?
Definition
 the torque increases
Term
 How do you calculate the torque if the force is at an angle?
Definition
 find the y component and multiply by the l
Term
 the more mass, the more____.
Definition
 inertia
Term
 What are the characteristics of rotational inertia?
Definition
 varies with the radius and distribution of mass; as the radius increases so does the intertia; as the distribution is further ot the inertia increases
Term
 Why does a tight rope walker carry a long pole?
Definition
 it gives him a vetter moement of inertia so he doesnt fall
Term
 Why do we bend our knees more when we run?
Definition
 it reduces our moment of inertia
Term
 Where is the center of gravity of a bicycle tire located?
Definition
 the middle
Term
 What is unstable equilibrium?
Definition
 the center of gravity goes lower and is easy to turn over
Term
 What is stable equlibrium?
Definition
 the center of gravity must go up; hard to turn over
Term
 What is neutral equlibrium?
Definition
 center of gravity stays in the same place (ball)
Term
 When you balance an object, are you balancing weight or torque?
Definition
 torque
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