GIVEN that

• there are today one billion cars on the earth.
•  the average car travels 15,000km a year and uses 1 liter to travel 12km.
•  Global oil reserves were calculated to be 1,383 billion barrels in 2010.
• One barrel is 159 liters of oil.
• One barrel can give 146 liters petrol and diesel.

CALCULATE

• Given that the number of cars in the world remains steady and if the world only uses oil for its cars, ESTIMATE how many years can we carry on driving.

NOTES

One billion = one thousand million: it is written as 1 000 000 000 or 10⁹

See the challenge below. A city with boundary at B is surrounded by land that feeds it. The food is taken to town by horse and cart. No fossil-fueled transport is available. Neither is any renewable transport like rail or sailing boats on canals. Boundary A is the outermost limit from which food is brought in. C is the center of the city and the distribution point farthest away from the outer boundary.

Assume for the sake of simplicity that a horse and cart is to come into the town to deliver oats to point C for distribution from point A. And that the horse and cart will return to point A for the next load. Assume as well that the horse needs to eat the oats to be able to pull the load.

Now, the horse cannot eat all the oats on the cart during the journey, or that would make the exercise pointless. As the horse has to return it can neither eat half the oats during the journey. Personally I would think about 10% per direction (20% in all) would be acceptable but you may take your own amounts. (Please show this carefully in your working)

THE TASK

Calculate using this model the maximum size of a city that is independent on fossil fuels. I maintain that the maximum size of a sustainable city is well under one million inhabitants, meaning that the majority of cities in the world today are at a high risk of starvation due to fossil fuel shortages. I would be happy is someone could prove me wrong.

Show all your working and clarify your assumptions.

Helpful data is given below.

• Although horses eat grass, they need oats.
• Imagine then a horse carrying food from the area of production to the city where the oats will be consumed.
• The driver feeds the horse the oats from the cart.
• Is there a way the answer to this problem could illustrate for us the maximum size of a city? Surely the horse should arrive with its load mainly intact. If the horse has to carry the oats so far that it eats up the load (and has none for the return journey) then sending the oats to the city is pointless.
• An average horse is about 750kg to 800 kg.
• It can pull two times its own weight.
• A draft horse can pull a dead weight along the ground (draft) equal to 1/10 their body weight for 8 hours a day.
• A wagon weighing 1,8 tons takes four horses to pull it.
• For simplicity, let us say the wagon weighs 0,8 tons and carries a ton of oats.
• A grain feeding of only .3% of body weight is all drafts need they can survive on grass they find by the roadside for the rest of their diet.
• City density ranges from 30,000 per km2 to suburbs of 1200 per km2. Suburbs deemed pleasant to live in have 5-6000 per km2. Dense city centres have around 12,000 per km2.
• When working in the harness all day, each horse will eat about 4.5 – 7 kg of grain and about 13,5 kg of grass or hay a day. Note – as the distance pulled increases so does the amount of grain I feed.  When pulling  30 km a day, calculate 9 kilos of grain per horse each day
• For help with calculation the size of the area that will feed the city a rule of thumb is that you need one hectare of agricultural land per family of 4. See more on that aspect in the earlier post here.

Imagine then a horse carrying food from the area of production to the city where the oats will be consumed.

The driver feeds the horse the oats from the cart.

Is there a way the answer to this problem could illustrate for us the maximum size of a city? Surely the horse should arrive with its load mainly intact. If the horse has to carry the oats so far that it eats up the load (and has none for the return journey) then sending the oats to the city is pointless.

Some basic data

A average horse is about 500 kilos say.

It can pull two times its own weight.

A grain feeding of only .3% of body weight is all drafts need they can survive on grass they find by the roadside for the rest of their diet.

This is the first shot at this problem, comments and additional data sets would be appreciated.

City centres have much more, from 12,000 upwards.

However, around 40% of the area of these cities is allocated to car transport system – for example, roads, garages, parking spaces, car showrooms, repair shops and so on.

If the car transport system were to be abandoned, how dense could cities get and still retan the feeling of a density of 5000 per km2?’

If we who live on Earth stand and hold hands with each other, would we be able to form a circle around the Earth?

Given that the average comfortable reach is about 1,2 meters hand to hand.

Given that there are 7 billion people on the Earth

Given the circumference of the Earth is 40075  km

State whether  the following is true or false: if the World population gathered at the Equator, could they, holding hands, create a human chain to encircle the world?

Next: how many times could the world be encircled if this is true?

If we could form a line holding hands around the world, what percentage of the world’s population would be needed?

And that the density of cities ranges from

Mumbai – nearly 30,000 per square km

Through Sao Paolo at 9,000

Through London at 5,000  to

Copenhagen at 1,800

How much space would be needed for these different variants?

For inspiration see the website PER MILE.

For the densities of the top 125 cities see the City Mayor’s site here.

Given that the agricultural land needed to feed a family of four is about one hectare.

Given that only about 30 % of land can be farmed.

Given that the population density of cities can be around 5000 inhabitants per square kilometre.

Calculate:

If the city is circle-shaped, what would its radius be in kilometres?

What would be the radius of the area around the city, needed to feed the city’s inhabitants?

If the land around the city could be farmed 100%, what would the radius of the farming area/food production area be?

Extra work:

Find out the population of a city near you, and its density.

Work out how much agticultural land would be needed to feed it according to the above.

Create a map of the city and its area around it showing how far its food circle extends.

The average car in Europe weighs 1.5 metric tons (1500kg)and in the US: 2 tons (2000kg).

GIVEN:

One litre of petrol weighs 0.737 kg and one litre of petrol gives rise to 2.32kg of carbon dioxide.

GIVEN:

The European Fuel Efficiency Regulations demand maximum  5 litres per 100km.

Calculate:

How far must you drive in order to emit a weight of carbon dioxide equivalent to the weight of the car?

Present:

Give an idea of what the distance stated as your answer in Calculate means (for example how many trips between major cities in your country, or how many commutes to and from work – state the average car commuting distance of course).

The atomic weight of carbon is 12 and oxygen 16.

As carbon dioxide has two oxygen molecules (CO2):

The total weight of carbon dioxide is  12+16+16 =44

CALCULATE:  if your car emits one ton (1000kg) of carbon dioxide, how much of this is carbon?

READ MORE: calculate how far you must drive to emit 1000kg here.