When I first learned how to ice skate, my teacher taught us to do fishies with our feet. We would have the heels of our feet touching, then we would push outward and then push inward until our toes touched. Our feet would make an oval shape that kind of looked like the shape of a fish.
Why was I able to move my feet on ice so easily? In fact, the slipperiness of ice always made me feel like I would slip and fall.
The smoothness we feel when we move our hands over a surface has to do with the fact that surface has little friction. Friction is the amount of resistance that one object has with moving over another.
There are two types of friction: static friction and kinetic friction. Static friction is friction between two things that aren’t moving relative to each other. For example, a rock sitting on top of a table is exhibiting static friction. Kinetic friction is the resistance between two objects that are moving. For example, a box moving against the floor is exhibiting kinetic friction.
Atoms can experience friction as well. If a metal box starts getting compressed, the atoms moving inside will create internal fiction. Friction causes things such as fire (when you rub sticks together, the friction from the rubbing creates the fire). So ice’s smoothness should come from the fact that its friction is less, right?
A long thought theory had to do with the fact that ice is less dense (density is the amount of stuff an object has divided by the amount of space it takes up, or mass divided by volume) than water (which is why ice floats on water).
When someone with ice skates steps on ice, the high pressure (due to the fact that the surface area of the skates is very small) causes the ice to melt and thus become liquid water. But this theory doesn’t make sense because there are activities where the surface area is lower, making the pressure lower, and the ice is still as slippery as it was.
Another theory says that moving on ice causes friction to heat up water and create a water layer, which is what makes it slippery. But this one doesn’t make sense either because, as an ice skater can attest, standing still on ice is also pretty slippery.
Since ice is a solid substance, its molecules are packed together. Each water molecule crystal inside ice is bonded to three others. But the molecules on the surface can only bond to two others, weakening their bonds. Slipping on ice is caused by these surface molecules rolling over. But, these molecules aren’t like liquid water. They’re like gas.
When ice is far away from its melting point, like around -40 degrees, it is similar to sandpaper. At really, really low temperatures (the lower the temperature, the less kinetic energy the molecules have), the ice doesn’t have enough energy to break free and roll over and so it’s not as slippery. The highest temperature for slipperiness is about 19 degrees.
The answer to what makes ice slippery is anything but simple and there is still much research to do on this topic. But, having things that are still kind of (or in other cases, fully) a mystery makes our world beautiful.
Vaageesha Das is a senior at Morgantown High School.
Information comes from:
- Fore, M. (2018, May 21). Why is Ice slippery? Why Is Ice Slippery? https://www.livescience.com/62621-why-is-ice-slippery.html;
- Ghose, T. (2013, June 4). What is friction? What is Friction? https://www.livescience.com/37161-what-is-friction.html
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