Simply Strange Physics

QUESTION #1: Does ice become slippery before or after someone steps on it?

Have you ever wondered why ice is slippery when you skate? Probably not, but now that the question is out there could you answer it? Scientists of the past rationalized that the pressure on the ice (applied for instance by an ice skater) caused the top layer of the ice to melt, in theory leading to a small layer of water to form on the ice and voila the ice becomes slippery. If you are wondering why this is a convincing argument well, the answer is that water is less dense as a solid (ice) than a liquid which means it holds the ability to have a lowered melting point caused by pressure. BUT, what if the answer is not that simple? In today's scientific community this simple explanation is not widely accepted. The point is that the pressure of the skates will only lower the melting point of the ice by a very, very small percentage. With that being said the answer is sort of unknown, some scientists think that the friction from the skates melts the ice (but this leaves the door open to questions like what if the person is NOT moving at all is the friction still a valid answer?), while other scientists think that the water on top of the ice is a natural occurrence made of unstable water molecules searching for stability (meaning they are in constant random motion).

ANSWER #1: Unknown! (However, the theories of a thin watery layer on top of the ice or friction and even some pressure probably play into the slipperiness of ice)

Websites Consulted;

http://mentalfloss.com/article/53650/why-ice-slippery
http://www.livescience.com/32507-why-is-ice-slippery.html
http://dujs.dartmouth.edu/questions/what-causes-ice-to-be-slippery#.VoGSOpMrJEI

QUESTION #2: Is foam a liquid, solid or gas?

To really understand foam try holding it, can you make the determination -- is foam a solid, gas or a liquid (use the chart above if you want to review the basic properties of solids, liquids and gases).We use it every day when washing dishes, shaving, taking a bubble bath but do we really know the weird foam that permeates our lives? The answer is no. Actually as far as research has shown me no real theories exist on the stiffness of foam when looking at variables like bubble sizes or ingredients. Ironically, this is valuable information when for instance filling the cracks in buildings (no one wants bugs to easily squeeze through into their home). So, we know it is important but do we know it on the most basic of levels, can we determine if it is in fact a solid, gas or a liquid. There are many people who think foam is either a liquid or solid one or the other simply aerated with a gas. But this is because they are looking at the components, not the characteristics. When looking at a simple shaving cream well the line is harder to draw, since it holds it shape like a solid for a short period of time however, when left overnight it losses its shape being left as a layer of soap. But, unlike solids it will take the shape of a container (shaving cream containers being a prime example). This leads to the question, if a aerated liquid shows properties and characteristics of both liquids and solids what exactly is it?

*Note, in this example we were looking at liquid aerated foams NOT solid aerated foams like sponges which are actually solids with many air holes.

ANSWER #2: Liquid Aerated foam has the properties of both solids and liquids, but has a bunch of gas in it, so it is hard to say, it can be argued depending who you are and how you classify a compound.

Websites Consulted:

http://science.nasa.gov/science-news/science-at-nasa/2003/09jun_foam/
https://www.quora.com/Is-foam-a-liquid-a-solid-or-a-gas
http://mypages.iit.edu/~smart/hallden/lesson1.htm
https://en.wikipedia.org/wiki/Foam

QUESTION #3: Why are cheerios magnetic?

The Cheerios effect; when objects float on a surface and seem to attract each other. Example: if you put one cheerio in the milk it will create a small indent if you put another one in it makes its own dent and as the cheerios come closer and closer together at a point they can appear to act like magnets and stick together! The reasoning is that the barrier between the air and the liquid surface creates surface tension, the milk to air barrier does not like to bend in any way, but the force of gravity it still acting on the cheerio pulling it down which leads to a slight deformation with a floating object at the centre. When you add another cheerio into the mix it has the same outcome with a slight modification if the two cheerios get close enough one will fall into the others dent as if they are attracted to each other.


Alright, so we've answered one of the magnetic questions about cheerios but not the other, why can I use a magnet and pull a cheerio through water? There are two answers, one being that breakfast cereal is fortified with iron and iron is attracted to magnets. If you crush the cereal into a fine dust and put a magnet to it then you will see some of the cereal bits sticking to the magnet therefore it isn't the water but the ingredients of the cereal leading to the magnetism.  However, other objects with NO iron content will also be 'attracted' towards a magnet when left to float on water, the reason is the diamagnetic property of water meaning the water when exposed to a magnetic will actually produce a magnetic field in the opposite direction as the one produced by the magnet in essence the water is repelled by the magnet leading to an dent being made for the non-magnetic object to fall into, the object will continue to fall into the indent as the magnet is drawn across the water surface.

 

What the two magnetic field of water vs. magnet create, diamagnetism is why there is an indent in the water. 

ANSWER #3: Diamagnetism and IRON

Websites Consulted:

https://en.wikipedia.org/wiki/Cheerios_effect
http://www.livescience.com/9350-cereal-science-floating-objects-stick.html
http://www.damtp.cam.ac.uk/user/dv211/cheerios.html
http://io9.gizmodo.com/5514825/the-cheerio-effect
https://www.kjmagnetics.com/blog.asp?p=cereal-contains-iron

The Mpemba Effect

WORD WALL:

Nucleation: the timeframe the observer needs to observe something until it changes structures/phases. Nucleation is effected by impurities.

Have you ever wondered why on occasion hot water freezes faster then cold water? We all know it happens but the reasoning is a bit more challenging to grasp.  There are many theories to explain this conundrum labeled the Mpemba Effect and they go as follows:

1. Hot water will evaporate faster which means there is less volume for freezing. Or the faster evaporation an endothermic process cools the water faster. 
2. Cold water forms a frost layer which acts as an insulator. 
3. Solutes (like carbon dioxide) quantities alter the hot water from the cold water since when the hot water is heated these quantities change. 
4. The freezing point is affected by the impurities inside the water (like dust, or salts), which have nucleation temperatures. 
5. Warm containers enable better thermal conduction with the freezer, which means that heat is conducted better. 
6. The bonds in the actual water have unique properties that cause this weird effect. Specifically the hydrogen bonds, which lead to many of water’s weird properties, like high boiling points. The theory is that the water molecules are pulled close together by the hydrogen bonds leading to the repulsion in the covalent bonds to stretch out the bonds and store lots of energy, the heated water stretches the hydrogen bonds which allows the covalent bonds to lose some of their stretch and energy which leads to faster cooling, this along with normal old freezing makes the hot water freeze faster then the cold water.  
7. Hot water cools quicker due to the larger difference in temperature between the hot water and the cold freezer, which allows it to reach its freezing point before the cold water has time to reach its own freezing temperature.
8. Supercooling can be described as when water freezes at a temperature lower than the known freezing point of zero degrees Celsius if the water reaches a temperature lower than zero then it may want to be in the solid lattice formation but may not know how to actually form this pattern (requiring a nucleation site to provide the instructions which on occasion takes time for the molecules to find below their freezing point). Cold water is shown in some experiments to actually supercool more than hot water and this time and effort preformed by the cold water means a slower freezing. 

Looking at the name of this phenomenon I was wondering where it came from and like so many other theories it was named after its founder who was actually a Tanzanian high school student doing tests on ice cream (hot ice cream freezes faster than cold ice cream) -- this being said other people in history probably saw the effect first since there are actually notations of the effect made by Aristotle and other famed scientists.

All right so we've go the theories but we do not understand the basics of water and how it freezes. Temperature is all based on energy in the molecules; heat ergo can be directly related to the amount of energy. More molecules are in more water and more molecules means more potential energy storage which goes back to temperature. As thermal energy in the water decreases so does temperature and once zero degrees Celsius is reached the water will start to freeze, this temperature is known as the freezing point. Conduction helps with freezing in order for water (a liquid) to freeze it must be in some type of container the container sits on the freezer and as it gets cold the water gets cold, so using conductive materials like metals can speed up cooling since the conductive material can easily transfer the cool temperature to the water. In the freezer there is also cold air, which will exchange the hot air from the water with the cold air in the freezer quickening the freezing. Evaporation leaves the lower energy molecules behind; less energy as we've established means less heat this lowers the temperature. The process of convection also aids in water freezing, one example being that the cold water is denser then hot water so the cold sinks to the bottom of the container this leads to convection currents. The problem is that if the water moves too much then the process of freezing actually slows down. All these factored are important to note when looking at the Mpemba Effect and are what led to the theories looked at in the list above.

In the end conclusions are hard to draw, the only answer is that there are many possible answer and one of them or maybe a bunch of them are correct or maybe a combination of these theories answers the weird, wonderful question left by the Mpemba Effect.

Watch this video for a summary of the Mpemba Effect:

Websites Consulted

http://phys.org/news/2010-03-mpemba-effect-hot-faster-cold.html
https://medium.com/the-physics-arxiv-blog/why-hot-water-freezes-faster-than-cold-physicists-solve-the-mpemba-effect-d8a2f611e853#.qme2mhyeg
http://www.school-for-champions.com/science/mpemba.htm#.Vn8dwpMrJEI
http://math.ucr.edu/home/baez/physics/General/hot_water.html