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Human Power vs. Horsepower: the future of sustainable transportation- Teacher Resource Page

with Dr. Bradley Layton

2:15- Introduction: “unless you can measure something, unless you can talk about it in numbers, you really don’t know what you’re talking about…” 4:30- Personal introduction… 9:10- Human powered water and aircraft at MIT… 11:15- Discussion about different modes of transportation… 13:00- Human vs. horse power introduction… 15:45- Calories, Joules, and measurements of power energy… 21:00- How many joules do you need per day?… 27:00- Energy vs. power… 28:10- What is a Watt?… 30:50- How much power do you have?… 36:30- Conversion of Watts into horsepower… 38:00- Human vs. horse power conclusion… 40:00- Renewable energy projects at the University of Montana… 41:30- Overview of larger program/ homework for students… 45:00- Question & answer…

Human Powered Vehicles

Human powered vehicles, or HPVs, are vehicles that rely entirely on power supplied by human muscles for propulsion. The most common type (and largest subgroup) of HPV are bicycles, but there are many different types of HPVs; some can fly through the air or traverse water, and other groups of land-roving HPVs offer better postures, more protection from the elements, or have other advantages compared to standard bicycles. Mechanical engineers are working, in competitions and elsewhere, to create the best design for various types of human powered vehicles. Though many vehicles are built for hobby, or only with speed in mind, others see HPVs as an opportunity to create a more sustainable future. According to HPV enthusiast and entrepreneur Cameron van Dyke, “It is about questioning our country’s energy use, health, safety, and access to travel. … My hope is to get people to imagine new possibilities for the way we travel.”

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Not Just a Weird Hobby
Although much of the internet chatter around HPVs focuses on which incredibly uncomfortable machine can travel the fastest, engineers like Mark Archibald have more practical ideas in mind: “In developed countries, those types of vehicles, along with more conventional bicycles, can be used to relieve traffic congestion, improve public health, reduce air pollution and significantly lower transportation costs. In developing countries, human-powered vehicles can provide affordable basic transportation for personal transport, deliveries and even ambulance services… [HPVs] are affordable, clean and safe. They are faster and more comfortable than standard bicycles, and many offer protection from foul weather.”
-Via LiveScience.

Discussion Questions

From bikes to kayaks, human powered vehicles are everywhere. How many human powered vehicles have you used? Do you use any regularly?

What are some benefits of human powered transportation? What are some limitations? How might human powered transit be different in a city than it would be on the country side/suburbs?

Do you think human powered transportation will become more or less popular and widespread in the future? Why?

How can human power be augmented to create a more sustainable future, while maintaining convenience?

Additional Resources

“The World’s Fastest Human Powered Vehicle” (engadget.com)

“9 Unusual Human Powered Contraptions” (Popular Mechanics)

“The Future People Push the Boundaries of Human Powered Transport” (gizmag.com)

Quattrocycle familiefiets (YouTube)

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Human vs. Horse Power: how do we measure power?

Much of Dr. Layton’s talk is focused on the ideas of energy and power, and more specifically, how much energy and power we consume and expend in a day. To do this, he breaks down the mathematics of “human power” and compares it to a metric we are all familiar with: horse power. In the talk, there is a lot of discussion about unit conversion and the order of operations needed to calculate a human’s energy and power use. In his calculation, he finds that eight humans can produce a bit more than a horsepower of energy. So, in theory, a group of eight average humans could beat one average horse in a game of tug of war (although it doesn’t always work that way in practice). Click below for a more detailed look at the math behind that calculation, and additional resources with help with unit conversion.

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Relevant Units:
1 cal= 4.184 J   1 Kcal= 4.184 kJ
1 W= 1 J/s   1 kW=1 kJ/s

Humans Power:
~2,500 Kcal/day= 10,500 kJ/day
10,500 kJ/day= .122 kJ/s
.122 kJ/s= .122 kW= 122 W

Horse Power vs Human Power:
1 horsepower= 746 W
1 “humanpower”= 122 W
122 W/person x 8 people= 976 W
8 “humanpower”> 1 horsepower

Discussion Questions

A human can produce roughly 1/8th of a horsepower. Does this number surprise you? Did you expect it to be higher or lower?

Does the knowledge of the amount of power that humans can produce change your perception of human powered vehicles? Why or why not?

Additional Resources

Unit Conversion within the Metric System (Kahn Academy)

The Encyclopedia Britannica’s entry on Horsepower

Forum on Horsepower vs. Man Power (The Popular Machinist)

Human Powered Crane (YouTube)

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