Explain the geographical conditions suitable for ice skating (in a few words)
Answers
Ice skating, the recreation and sport of gliding across an ice surface on blades fixed to the bottoms of shoes (skates). The activity of ice skating has given rise to two distinctive sports: figure skating, which involves the performance of various jumps, spins, and dance movements; and speed skating and short-track speed skating, both of which are forms of racing on ice skates. Ice hockey is the best-known team sport that involves skating.
Answer:
A skate can glide over ice because there is a layer of ice molecules on the surface that are not as tightly bound as the molecules of the mass of ice beneath. These molecules are in a semiliquid state, providing lubrication. The molecules in this "quasi-fluid" or "water-like" layer are less mobile than liquid water, but are much more mobile than the molecules deeper in the ice. At about −157 °C (−250 °F) the slippery layer is one molecule thick; as the temperature increases the slippery layer becomes thicker.
It had long been believed that ice is slippery because the pressure of an object in contact with it causes a thin layer to melt. The hypothesis was that the blade of an ice skate, exerting pressure on the ice, melts a thin layer, providing lubrication between the ice and the blade. This explanation, called "pressure melting", originated in the 19th century. This, however, did not account for skating on ice temperatures lower than −3.5 °C, whereas skaters often skate on lower-temperature ice.
In the 20th century, an alternative explanation, called "friction melting", proposed by Lozowski, Szilder, Le Berre, Pomeau and others showed that because of the viscous frictional heating, a macroscopic layer of melt ice is in-between the ice and the skate. With this they fully explained the low friction with nothing else but macroscopic physics, whereby the frictional heat generated between skate and ice melts a layer of ice.[ This is a self-stabilizing mechanism of skating. If by fluctuation the friction gets high, the layer grows in thickness and lowers the friction, and if it gets low, the layer decreases in thickness and increases the friction. The friction generated in the sheared layer of water between skate and ice grows as √V with V the velocity of the skater, such that for low velocities the friction is also low.
Whatever the origin of the water layer, skating is more destructive than simply gliding. A skater leaves a visible trail behind on virgin ice and skating rinks have to be regularly resurfaced to improve the skating conditions. It means that the deformation caused by the skate is plastic rather than elastic. The skate ploughs through the ice in particular due to the sharp edges. Thus another component has to be added to the friction: the “ploughing friction”.The calculated frictions are of the same order as the measured frictions in real skating in a rink.The ploughing friction decreases with the velocity V , since the pressure in the water layer increases with V and lifts the skate (aquaplaning). As a result the sum of the water-layer friction and the ploughing friction only increases slightly with V, making skating at high speeds (>90 km/h) possible.