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Burning food experiment - could some explain these results please?

Discussion in 'Science' started by 1000trees, Nov 24, 2007.

  1. I have been doing a burning dried food experiment for the past couple of years - linked to the amount of energy in each food. They set fire to small piece of dried food in a candle flame. I always use crisps, dried banana, pasta and sometimes toast. I often give them moist banana to show that it doesn't burn. They only burn a small amount, roughly the same size of each one. The dried banana wins hands down every time, with the crisp second.

    However, when you look on the back of food labels, energy per 100g, crisps have much more as well as a higher content of fat. Surely this should burn longer?

    I have always explained this in the past as the banana having lots of "slow release" energy as opposed to crips.

    Can anyone explain this in simple terms - it is for primary children and 'keeping healthy' - or perhaps suggest changes to this experiment.
     
  2. I have been doing a burning dried food experiment for the past couple of years - linked to the amount of energy in each food. They set fire to small piece of dried food in a candle flame. I always use crisps, dried banana, pasta and sometimes toast. I often give them moist banana to show that it doesn't burn. They only burn a small amount, roughly the same size of each one. The dried banana wins hands down every time, with the crisp second.

    However, when you look on the back of food labels, energy per 100g, crisps have much more as well as a higher content of fat. Surely this should burn longer?

    I have always explained this in the past as the banana having lots of "slow release" energy as opposed to crips.

    Can anyone explain this in simple terms - it is for primary children and 'keeping healthy' - or perhaps suggest changes to this experiment.
     
  3. maybe a silly question but I assume you're burning the same mass?
     
  4. Are you using a calorimeter or just timing how long it takes something to burn out?

    (The length of time something burns isn't necessarily an indication of how much heat energy is produced.)

    http://bioweb.usc.edu/courses/2004-fall/documents/bisc150...

    I'm no biologist, but I'm not sure the speed of burning relates to the speed of conversion in the body (?).

     
  5. specko: I'll just reinforce that this is primary school science so the experiment is conducted under rather less scientific conditions than it perhaps should be! I've never come across a primary school that has accurate enough scales. Perhaps I have been using too much banana?

    firrs: As I hinted at before, I have always explained the banana as being 'slow release' energy and the crisp being instant energy - it fizzes really well when you burn it. Is this correct? Or have I been teaching it incorrectly?

    Perhaps anyone can make suggestions to modify it? Obviously, with keeping health, I was rather hoping the banana would still be the best - Surely no one would recommend eating a bag of crisps before a long run/cycle ride because the energy is higher?

    It needs someone to spell this out to me!

     
  6. Hi,

    Basically your experiment contains far too many uncontrolled variables for it to actually give 'correct' results. For example;

    Mass differences
    How well they burn in air
    Water content (important for the above)
    Do they completely burn

    With the equipment available it is not possible to do an accurate experiment (this probably also applies to secondary schools).

    I would leave it with them getting the idea that this shows food contains energy then provide numbers for different food which they can then use.

    I am afraid your slow release energy explanation is way off the mark as your body gets the energy from food in a completely different way to simple combustion in air.

    Ger
     
  7. Thanks kevin, I just now looking for the answer to the 'energy' question. Picture the scenario: Class of 10 year olds looking at energy numbers on packets. They see that crisps contain 2000Kj per 100g - the highest of the lot. Cue questions to puzzled teacher about why crisps have been banned at breaktime over fruit when they would give more energy to work (albeit more slat and fat!). Cue questions about why marathon runners don't stuff themselves with crisps rather than pasta before they run. And I say...???
     
  8. Anyone for Kendal mint cake? :)

    How about some kind of practical analogy? Pass the parcel with a banana in many layers of wrapping paper and a chocolate bar (perhaps a fake one to avoid temptation) in only a few layers?

    The body has to do more things to extract the energy from the complex sugars in fruit than it does to get the energy from the refined sugars in confectionary.

    Or you could go with a candle and a pile of gunpowder :)
     
  9. Hi,

    Your question really relates to diet rather than the original experiment. In our diet its not all about maximum amount of energy per gram. We need lots of other things in a balanced diet i.e vitamins & minerals and roughage. With crisps as you say you take in lots of salt and fat so if you want to train for a marathon/run a marathon you would need to consume loads of packets of crisp which would soon take you over a sensible amount of fat and salt. With pasta there is not this problem as it gives you lots of large carbohydrate molecules without fat or too much salt. As you digest the pasta your body gradually gets lots of of small sugar molecules by breaking down the large carbohydrate molecule. The sugar can then be used to give you energy. Importantly this occurs over a long period of time (hours) hence you can run a long time before your body starts to use its own reserve of muscle carbohydrate (called glycogen).
    The problem with sugary foods like coke or sweets is that provide alot of energy they have to be used quickly by the body or stored as glycogen or fat. Hence they are useful when you need a burst of energy.

    Hope this helps.

    Ger

    (PS I have been known to run the odd marathon hence have looked into this)
     
  10. Sorry forgot to add.

    How do you explain this to 10 year olds. Not sure..... but you could get lots of empty crisps packets. It takes about 100 calories to run a mile so 2600 calories for a marathon. Then get them to work out how many packets of crisps they would be need to get this amount of energy and hence how much salt and fat that would amount to. Then give then the recommended daily intake for each so they can then work out why Paula Radcliffe is not sponsored by Walkers crisps.
    Hope this helps.

    Ger
     
  11. blazer

    blazer Star commenter

    Don't forget that a calorie (in dietary terms) is actually a kilocalory or 4,200J or 4.2kJ. Also you should be using J or kJ with your kids rather than calories otherwise we have to unlearn the imperial measure before they can learn the correct metric units. This is a constant problem with the kids I teach who don't have a grasp of the metric system at all and don't seem to pick it up at secondary either.
     
  12. coudn't you just show what 100g of banana looks like and what 100g of crisps look like to explain the KJ per 100g?
     
  13. As a secondary school teacher can i please beg primary school teachers not to steal our practicals. This is a fab practical for older children to analyse as there are lots of different aspects of science for them to get their teeth into. If they've already done the practical in primary school (to show something that even the class teacher seems unsure of) they just feel patronised by high school. There are lots of wonderful practicals for primary kids, please leave some for us.
     

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