My good friend Steve Beckelhimer posed an interesting question as to whether I could relate a problem on the energy concept I spoke of last time to rail and timber transport. Absolutely! If we consider a train in motion on a track, an important engineering principle is continuous tractive force. This is a force applied by an object pushing or pulling on another causing a change in velocity. This tractive force is inversely proportional to the velocity of the train. As the train speeds up, more fluid resistance
impedes the tractive force of the train. How can we quantify this continuous tractive force? Power is needed to propel the train. Power is the transfer or use of our good friend energy during a rate of time. Since energy and work are synonymous (demonstrated in the last blog entry) we arrive at the traditional definition of power=work/time -P=W/t. But we also know work is equal to force times distance on object moves - W=Fd. So, power is also equal to force times distance divided by time - P=Fd/t. Distance divided by time is velocity, which was being solved for on the physics question in the last posting. Now, we have arrived at power is equal to force times velocity - P=Fv or F=P/v. This is the equation engineers use to calculate the continuous tractive force for a train and it is derived from the concept of energy and its partner work.
Tuesday, May 22, 2012
Energy Follow-Up
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Very interesting. Can you apply physics to a falling tree in the forest. Can you answer this age old question: Does a tree make a noise when it falls in the forest with no one around?
ReplyDeleteThat depends on whether you hold true to the need for observation through sensory perception. Countless physical events occur that you and I do not observe, yet we do not discount them as not happening. I am not observing heat transfer, evaporation, or any of the immeasurable chemical reactions occurring in my body. Yet, they are accepted as physical events. And, this my friend is the issue. Observation through sensory perception is a pillar of science which helps to seperate it from other disciplines. The tree falls and a compression or density wave spreads out at 340 m/s. Our interpretation of the stimulus of the wave is predicated on us directly observing the event and our sense of hearing translating the event - your noise. As you can see, there is no absolute with this question. This may be why the question has been debated by physics students for generations. I will end with this in regards to the need for observation; it is the acceptable norm that an electron does not exist unless you have located its position - this would indicate that particle physicists insist on the observation and to them your noise would not exist.
ReplyDeleteThanks for the answer. This is definitely an answer that you should show to your students. You could pose the same question and have them come up with a logical inference on how to answer the question. I remember having a computer science teacher telling me of story on how he turned in a 20 page paper on solving 2+2=.
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