Posts Tagged ‘energy storage’

Angular Velocity of a Flywheel

Wednesday, October 4th, 2017

   We introduced the flywheel in our last blog and the fact that as long as it’s spinning it acts as a kinetic energy storage device.   Today we’ll work our way towards an understanding of how this happens when we discuss angular velocity.

   Angular velocity is represented in engineering and physics by the symbol, ω, the Greek letter Omega.   The term angular is used to denote physical quantities measured with respect to an angle, especially those quantities associated with rotation.

Angular Velocity of a Flywheel

Angular Velocity of a Flywheel

   

   To understand how angular velocity manifests let’s consider a fixed point on the face of a flywheel, represented in the illustration as A.   When the flywheel is at rest, point A is in the 12 o’clock position, and as it spins A travels clockwise in a circular path.    An angle, θ, is formed as A’s position follows along with the rotation of the flywheel.   The angle increases in size as A travels further from its starting point.   If A moves one complete revolution, θ will equal 360 degrees, or the total number of degrees present in a circle.

   As the flywheel  spins through its first revolution into its second, point A travels past its point of origination, and in two complete revolutions it will travel 2 × 360, or 720 degrees, in three revolutions 3 × 360, or 1080 degrees, and so forth.   The degrees A travels continue to increase with each revolution of the flywheel.

   Angular velocity represents the total number of degrees A travels within a given time period.  If we measure the flywheel’s rotational speed with a tachometer and find it takes one second to make 50 revolutions, point A will have traveled the circumference of its path fifty times, and A’s angular velocity would be calculated as,

ω = (50 revolutions per second) × (360 degrees per revolution)

ω = 18,000 degrees per second

   Next time we’ll introduce a unit of measurement known as radians which is uniquely used to measuring the angles of circular motion.

Copyright 2017 – Philip J. O’Keefe, PE

Engineering Expert Witness Blog

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What Came First? The Wheel or the Flywheel?

Monday, September 25th, 2017

   What came first?   The wheel or the flywheel?  Archeologists have been debating this question for decades.   One thing is certain, they both date back to prehistoric times.

What Came First? The Wheel or the Flywheel?

What Came First? The Wheel or the Flywheel?

   

   One of the oldest flywheel discoveries was a potter’s wheel, used to make pottery.   It’s a turntable made of stone or heavy wood that’s connected to a massive wheel by a spinning shaft.   Once the potter got the flywheel spinning with his hand or foot, the wheel’s heavy weight kept it in virtual perpetual motion, allowing the potter to concentrate on forming the clay he shaped with his hands.

   A potter’s wheel, or any other flywheel for that matter, takes a lot of initial effort to put into motion.   In other words, the potter must put a lot of his own muscles’ mechanical energy into the flywheel to get it moving.   That’s because its sheer weight binds it to the Law of Inertia and makes it want to stay at rest.

   But once the flywheel is in motion, the potter’s mechanical energy input is transformed into kinetic energy, the energy of motion.   The kinetic energy the potter produces by his efforts results in surplus energy stored within the flywheel.   Hence, the flywheel serves as a kinetic energy storage device, similar to a battery which stores electrical energy.   As long as the flywheel remains in motion, this stored energy will be used to keep the turntable spinning, which results in no additional mechanical energy needing to be exerted by the potter while forming pots.

   The flywheel’s stored energy also makes it hard to stop once it’s in motion.   But eventually the frictional force between the potter’s hands and the clay he works drains off all stored kinetic energy.

   Since the Industrial Revolution flywheels have been used to store kinetic energy to satisfy energy demands and provide a continuous output of power, which increases mechanical efficiency.

   Next time we’ll begin our exploration into the science behind flywheels and see how they’re used in diverse engineering applications.

 

Copyright 2017 – Philip J. O’Keefe, PE

Engineering Expert Witness Blog

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Electrocution by Microwave Oven

Sunday, August 21st, 2011

     Ever been jolted with electric current?  Like the time you’d just gotten out of the shower and went to plug in a lamp with damp hands?  So what do you think the voltage was that caused that nasty biting feeling that resulted from your momentary lapse in good judgment? 

     Once, while operating a subway car at a railroad museum at which I was a member, I was inadvertently “electrocuted.”  I went to turn on the lights inside the car, and unbeknownst to me the light switch was faulty.  When I touched it I instantly became connected to the car’s 600 volt lighting circuit.  With just a split second of contact the current passed through the tip of my right index finger, along my right arm, down the right side of my body, and out the tip of my big toe, finally exiting into the metal railcar’s body.  The current actually burned a hole where it had exited through my boot.  The experience was both frightening and painful, but fortunately did not result in any real injury.  I was lucky that the current had bypassed my heart, because if it hadn’t, I might not be alive today.

     That was 600 volts.  Now imagine being jolted by the 4000 volts present in a microwave oven’s internal high voltage circuitry.

     Last week we discovered how the high voltage circuit in a microwave oven converts the ordinary, everyday 120 volts alternating current (AC) present in our homes into a much higher voltage approximating direct current (DC).  This is done by an internal component known as the capacitor.  The capacitor is capable of storing large amounts of electrical energy, and this can result in microwave ovens presenting a danger even when unplugged.

     A microwave oven capacitor is shown in Figure 1.  If you happened to touch its wire terminals while it’s still charged, its power can rapidly discharge high voltage electrical current throughout your body.  The electrical current from the capacitor can even stop your heart from beating, and this is exactly what caused the demise of a person featured on a soon to be released Discovery Channel program, Curious and Unusual Deaths.  While being interviewed as an expert for the program, I was asked to explain this rather unique phenomenon of latent stored energy, and how it may present a threat.

Figure 1 – A Microwave Oven Capacitor

     Remember, a microwave oven capacitor can remain charged with dangerous electrical energy for hours, even days, after the microwave oven plug is pulled from the wall outlet.   The bottom line here is that you should not attempt to fix your microwave oven, unless you are trained and certified to do so. 

     Next week we’ll switch to a different topic, namely an electrical device known as a “wall wart.”  That’s the black plastic adapter you plug into electrical outlets to power your cell phones, laptops, and other small electronics. 

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