Sometimes, when night falls and the house becomes quiet, thoughts start to wander on their own. Then it can easily happen that curiosity takes complete control and reason, which tells you that it is bedtime, must give way. You examine one thing and along the way discover another thing that needs to be looked into – and so on. Until the night comes to an end and you go about the day in a half-asleep state.
Energy, for example, is something worth thinking about. We are in the process of depleting the Earth's energy resources at an accelerating pace. We have long been aware of this, but we refuse to fully acknowledge it. At least not to a significant degree. Driving electric cars might help a little, but unfortunately it is far too little. We live in a world of denial, along with a firm belief in miracles, that we will be saved when science provides a deus ex machina solution. Unfortunately, this is a phenomenon that belongs in the world of movies and novels. However, it may be that the world is beginning to wake up. If so, it is because of a young woman from Sweden who has made it her mission to awaken the world. Because we need change. Yet at the same time, the idea is associated with fear, for it is likely that these changes will hardly be very comfortable.
But if we let our thoughts spin a little in the night. Have you ever wondered how far a car could drive if it ran on slices of bread – or oats for that matter? Have you ever wondered how much gasoline you would need if we humans could run on gasoline?
Fortunately, the situation is such that we still have enough energy to run the internet. There, one can easily find basic data by doing a quick Google search. First, I looked at the daily energy requirements. From the Norwegian Health Informatics website, I obtained the daily energy requirements for women and men under different conditions, as shown in the table below. The energy requirements were given in kilocalories, a useless unit for calculations, so I immediately converted it to joules (kilojoules) and then to the amount of gasoline that contains the same amount of energy.
| OBJECT | ACTIVITY | ENERGY kcal | ENERGY kilojoule | Gasoline (liter) |
|---|---|---|---|---|
| Man age 40, height 180 cm, weight 80 kg | rest | 1732 | 7251 | 0,228 |
| easy work | 2772<7td> | 11605 | 0,366 | |
| activ work | 2945 | 12330 | 0,389 | |
| Woman age 40, height 165 cm, weight 60 kg | rest | 1354<7td> | 5668 | 0,178 |
| easy work | 2166<7td> | 9068 | 0,286 | |
| activ work | 2302<7td> | 9638 | 0,304 |
As shown by the table, we animals are considerably more efficient than machines. Yes, we are animals too, mammals and warm-blooded. Cold-blooded animals that do not use their energy to maintain body temperature are even more energy-efficient than us, but that can wait for another night. We do have an impressively low consumption – less than half a liter per day. Imagine how much gasoline it would have taken to build the pyramids if all the workers were gasoline-powered?
Then I also visited a website belonging to Ingrid Kristiansen. To reassure people who know me: I don't usually frequent such sites. It was just a one-time occurrence and solely for the purpose of finding information. What I learned on that site is how much energy we use on different activities.
| ACTIVITY | Energy/hour (kcal/h) | Energy/km (kcal/km) | Energy/km (kJ/km) | Petrol consumption (litres/km) |
|---|---|---|---|---|
| Hiking in flat terrain 5 kilometres per hour | 300 | 60 | 251 | 0,008 |
| Running 10 km/h | 660 | 66 | 276 | 0,009 |
| Running 15 km/h | 1080 | 72 | 301 | 0,01 |
Once again, one is amazed at how efficient we are. We also see that the most effective way to move is to walk – not run.
But what if we build an engine that runs on whole-grain bread with yellow cheese (without butter)? How much fuel would that require?
Many cars today consume about half a liter per ten kilometers. But gasoline engines are not particularly efficient. They have an efficiency of 20% (perhaps a little better with new engines, but in this calculation, we use 20%). This means that most of the energy is wasted as heat. Only 0.01 liters go towards moving the car forward one kilometer. That corresponds to an energy of 0.088 kWh, which in turn corresponds to 757 kcal. A slice of whole-grain bread with yellow cheese has an energy content of 152 kcal. This means that this car with a bread engine would need to chew through almost five slices of bread per kilometer. Then one would need to load a significant amount of fuel to drive a trip to Tromsø. Maybe one would also need to bring a stoker to feed this greedy machine. I really think we are going to have to scrap the car as a means of transport.
Comments. I have made it quite difficult to post comments on this page. This is to avoid having to clean out all those who try to sneak in shady links on the site. Comments are welcome via email. (click here) or post on Facebook page mine (opens in a new tab). Let's just hope that no major calculation errors have crept in!
