RESEARCH PROJECT : IS IT POSSIBLE TO WALK ON WATER ?

Cornflour Experiments

 

We had the idea to add cornflour in water to transform its viscosity and maybe allow a human to walk on this fluid. Indeed, it's a shear thickening.

 

 

      What is cornflour ?

 

“Cornflour” (called “cornstarch” in the USA) and popularly known under the name of “maizena”, is the white powdered starch derived from corn grain. It’s used in many ways, indeed it’s a famous food ingredient used to thicken sauces or soups. Moreover, it is used to make corn syrup and other sugars.

 

Cornflour is a polysaccharide and its chemical formula is : C6H10O5. It’s composed of starch molecules. It's available as semi-crystalline granules and its density is: 1,2 g/mL.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

http://www.africandelights.com.au/product.php?productid=1103306&cat=264&page=1

http://www.fourchette-et-bikini.fr/nutrition/maizena-ou-farine-27320.html

 

 

We can explain the change of reaction of the mixture water/cornflour, by looking at the molecular level: Indeed, starch molecules have rough and quirky shapes. When we mix cornflour and water, aqueous molecules form a fragile coat around starch molecules. In this envelop, they form some kind of balls which are able to slide and overlap one another. At the macroscopic level, the matter seems liquid.

But during a shock, this liquid becomes solid: at the molecular level, the membrane of water is destroyed for a short period of time. Starch molecules find their irregular form back and cling to one another: so the sliding is prevented.

 

 

      Properties of the mixture water/cornflour

 

Cornflour is a kind of flour, so it has a solid consistency. It’s known for its culinary and physical properties. With a certain quantity of water, cornflour will adopt a surprising consistency. Indeed, the mixture water/cornflour is an almost liquid fluid  But, when we exert a force on this fluid, its consistency changes and the fluid becomes solid immediately. So the limit between the solid and the liquid is very thin. Moreover, the consistency of this fluid varies according to lots of parameters: the quantity of cornflour and that of water, the force of the impact, the temperature of the mixture...

 

 

So we decided, thanks of experiments, to analyze the consistency of this fluid to finally determine if a human being could walk on it.

 

 

      First experiment

 

Aim of the experiment:

 

We wanted to determine the quantity of cornflour which is necessary to add in water to allow a person to walk on water.

 

Protocol:

 

We needed:

• A beaker of 100 ml

• Water

• Cornflour

• A spoon

• A scale

 

We decided to realize 3 different mixtures of cornflour and water, with 3 different proportions:

1. 25% of cornflour: 25g of cornflour with 75 mL of water (because 1 mL of water weighs 1g)

2. 50% of cornflour: 50g of cornflour with 50 mL of water.

3. 25% of cornflour: 75g of cornflour with 25 mL of water.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Observations :

 

First, we noticed that the first mixture was too liquid and that in the third one, there was not enough water compared to the quantity of cornflour.

Then, the second mixture was the most successful one, even if, according to us, it would have been necessary to add a little bit of cornflour.

With this mixture, we realized that when we mixed it slowly, the mixture obtained was liquid, but when we mixed it faster, it was harder to move the spoon: the fluid resisted.

 

 

      Second experiment

 

Aim of the experiment:

 

We wanted to show the properties of the mixture cornflour/water and at the same time, to determine the exact quantity of cornflour that would allow a human being to walk on this mixture.

 

Protocol:

 

We needed:

• A basin

• Water

• Cornflour

• A spoon

• A scale

 

 

 

 

 

 

 

 

 

 

 

 

 

 

We mixed gradually water with cornflour to finally obtain the perfect mixture:
200 mL of water with 470g of cornflour (either 470/1,2 = 392 mL). Indeed, on different websites, we found that the perfect proportions were a volume of water for two of cornflour.

With this information, we checked our results:  

200+392 = 592 mL

392/592 = 0,66 (either 66% of cornflour in the mixture)

So it seems that we found the right consistency.

 

Observations:

 

Now, we wanted to show the properties of the mixture cornflour/water thanks to a simple experiment: we just had to bring down a marble on the mixture and on the second video we showed, first the liquid consistency of this fluid with the spoon and then we heated it to show its solid consistency.

 

 

 

 

 

 

 

 

 

 

 

 

 

So we can  notice that the fluid offers a certain resistance and the marble doesn’t sink immediately: it first bounces on the mixture.

 

      Conclusion

 

So we can conclude that the mixture cornflour/water (with the good proportions) behaves as a viscous liquid when we manipulated it slowly but it becomes almost solid when we exert a pressure on it.

This video shows that humans can walk (or rather run) on this fluid:

 

 

 

 

 

 

 

 

 

 

 

 

 

https://www.youtube.com/watch?v=DhzKA__fkoE

 

In the video, they called the mixture cornflour/water "oobleck".

 

 

But we can't imagine walking on the water at a swimming pool, in a lake, a sea or even an ocean thanks to this method. Indeed, for an olympic swimming pool we would need                        (metric tons) of maizena, for the Mediterranean Sea                         and for the Atlantic Ocean                          !

 

Calculations: