; Rotational Quantities
Learning Center
Plans & pricing Sign in
Sign Out
Your Federal Quarterly Tax Payments are due April 15th Get Help Now >>

Rotational Quantities


  • pg 1
									Rotational Quantities

    Going in Circles
Rotation vs Revolution
 Rotation is to spin on an axis, like a wheel;
 Revolution is to travel in a circle around a
  center point, like cars on a race track.
 Forces which cause motion in a
       circle (revolutions)
 If an object is moving in a circle there is a
  centripetal force causing the curving.
 Centripetal means “center-seeking”
 There are no centrifugal forces!
 In space, gravity is the force that causes the
  Moon to orbit (revolve around) the Earth,
  and the Earth to orbit the Sun.
 That makes it a centripetal force!
 Newton was the Physicist who first
  described mathematically gravity.
    Newton’s Law of Universal
 Every object in the universe attracts every
  other object with a force directly
  proportional to the product of their masses
  and inversely proportional to the square of
  the distance between their centers.
 Formula to follow:
An Inverse Square Law!

        F G 2
But Why?
 Newton didn’t say why, he just derived the
 In the centuries to follow, many laws were
  shown to be inverse square proportions.
 The reason has to do with a “flat” universe
  and Euclidean geometry.
 Einstein changed all this, but we’ll stick
  with Newton.
   Forces that cause an object to
 Torques cause objects to spin on their axis.
 A torque is a force acting over a length.
 The length is called a lever arm.
 F1L1 = F2L2, as in a seesaw or mobile.
 Steering wheels, crowbars, and doorknob
  placement are all uses of torque.
 The center of gravity is where all the weight
  of an object appears to be.
Rotational Inertia
 Objects rotating tend to keep rotating.
 As linear inertia is related to mass,
  rotational inertia is related to moment of
 The moment of inertia (nothing to do with
  time) is how an object’s mass is distributed
  around an axis.
Keep on Rotating!
 The conservation of rotation, so to speak, is
  called the conservation of angular
 When an ice-skater spins slowly but then
  pulls her arms in, she speeds up because of
  conservation of angular momentum.
 Combining angular momentum and torque
  (in very mathematical ways) produces a
 The slow turn around the vertical axis of the
  suspended bicycle wheel.
 As the World Turns (ahem), the torque
  produced by the Sun and Moon on our
  planet causes the Earth to precess every
  25,000 years.

To top