What is the effect of air resistance on the conservation of energy?

Sebastianebilly · 02-17-13, 07:38 PM

In conservation of energy, for example throwing a ball up and catching it, how does air resistance (non free fall) impact the conservation of energy? Is it because energy is lost due to work done on the air?

SolarUtah · 02-18-13, 12:00 AM

Air resistance can play a huge roll in energy use. I will try to explain this in terms those who are not engineers in the forum will understand.

Wind resistance, or drag increases to the square of the speed or velocity. This means if you double the speed, the resistance to movement or drag will increase 4 times.

At the same time, if you double the speed, the amount of horsepower will increase 8 times.

So you can see that limiting wind resistance or drag can save huge amounts of energy.

In the HVAC industry, I have worked on projects where they doubled the free area of ductwork, just to reduce noise. This resulted in having to slow down the fan RPM and saved about 60% in energy costs, just from changing the size of the ductwork!

I have also read about aerodynamic changes to large 18 wheel trucks where they double the MPG, although some of the changes may be mechanical in nature as well.

Hope this helps answer your question.

kabutomushi · 02-22-13, 06:53 AM

To answer your homework question, since energy is conserved in all cases, air resistance is simply part of the conservation of energy. Any energy lost to air resistance may make it look that energy is not conserved, but if you add in the air resistance, it is indeed conserved. Tossing a ball up and catching it in a vacuum would mean the ball would fly farther up before stopping and would hit the hand at a higher speed than in atmosphere. Could you measure it? It would probably be measured in a few tenths of milimeters, given the force of gravity being so much larger than the air resistance of a tossed ball.

02-17-13, 07:38 PM	#1
Sebastianebilly Lurking Renovator Join Date: Jan 2013 Location: New York Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts	What is the effect of air resistance on the conservation of energy? In conservation of energy, for example throwing a ball up and catching it, how does air resistance (non free fall) impact the conservation of energy? Is it because energy is lost due to work done on the air?

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02-18-13, 12:00 AM	#2
SolarUtah Cheap Renovator Join Date: Jan 2013 Location: Utah Posts: 10 Thanks: 0 Thanked 1 Time in 1 Post	Air resistance can play a huge roll in energy use. I will try to explain this in terms those who are not engineers in the forum will understand. Wind resistance, or drag increases to the square of the speed or velocity. This means if you double the speed, the resistance to movement or drag will increase 4 times. At the same time, if you double the speed, the amount of horsepower will increase 8 times. So you can see that limiting wind resistance or drag can save huge amounts of energy. In the HVAC industry, I have worked on projects where they doubled the free area of ductwork, just to reduce noise. This resulted in having to slow down the fan RPM and saved about 60% in energy costs, just from changing the size of the ductwork! I have also read about aerodynamic changes to large 18 wheel trucks where they double the MPG, although some of the changes may be mechanical in nature as well. Hope this helps answer your question.

02-22-13, 06:53 AM	#3
kabutomushi Kabuto Join Date: Mar 2010 Posts: 7 Thanks: 0 Thanked 0 Times in 0 Posts	To answer your homework question, since energy is conserved in all cases, air resistance is simply part of the conservation of energy. Any energy lost to air resistance may make it look that energy is not conserved, but if you add in the air resistance, it is indeed conserved. Tossing a ball up and catching it in a vacuum would mean the ball would fly farther up before stopping and would hit the hand at a higher speed than in atmosphere. Could you measure it? It would probably be measured in a few tenths of milimeters, given the force of gravity being so much larger than the air resistance of a tossed ball.