Here’s a cool calculation from Angela Coburn of ubc.

This is part of Physics 420 where they learn to demonstrate physics to the public.

I think this is an awesome idea to teach young physicists to discuss and demonstrate physics to the general public (including children).

This is great for the cause of physics and for any individual who works in the field.

I realize that the purpose of these calculations isn’t to model the situation perfectly but it’s to open the door to understanding.

I’m curious if anybody has any comments or other ways of performing this calculation.

I also noticed Zach Hulbert from the same class did a blurb on the Physics of Rubber Bands.

First, I measured the force exerted on the propeller by the twisted rubber band.  I did this by using a digital scale.

After twisting the rubber band, I placed the outside edge of the propeller on the scale, as shown in the following picture.

The scale measured in grams, so I needed to convert this to Newton’s.

Where,

m = the reading on the scale

a = 9.8 m/s²

Then I measured the radius of the propeller and calculated the work.

Where,

F = the previous calculation

d = 2πr X (number of turns)

Then the power could be calculated by measuring the time it takes for the propeller to unwind.

Where,

W = work

t = time in seconds

These calculations can be seen in an excel spreadsheet here, Spreadsheet. (RubberEnergy1)

In order to calculate the transport cost, the glide slope was determined by measuring how far the airplane “glided” when launched without the propeller powering it.  This was done several times to get an average estimate.

Where g is the acceleration due to gravity.

Note: the units of transport cost, m/s² are equivalent to J/kg/m

Then convert the units to kWh/tonne/km and compare to a Boeing 747.

1kWh = 3.6MJ

Link to excel spreadsheet, Transport Cost (transport_cost)