Skates

If ice were more dense than water, skating would be a lot less popular. 

It has been suggested that the pressure exerted on a skate Made is sufficient to melt the ice beneath it and form a thin film of water which makes it easier for the blade to slide over the ice. Assume that a skaterweighs 120 lb and the blade has an area of 0.10 in2. Calculate the pressure exerted on the Made (1 atm = 15 lb/in2). From information in the text, calculate the decrease in melting point at this pressure. Comment on the plausibility ofthis explanation and suggest another mechanism by which the water film might be formed. 

Sprinkled throughout the text are a number of short notes in the margin. Many of these are of the now, hear this variety, others are mnemonics, and still others make points that we forgot to put in the text. (These were contributed by your fellow students.) Some—probably fewer than we think—are supposed to be humorous. See, for example, the reference to ice skating on page 239 through five editions WLM thought it was uproariously funny. 

Because people everywhere tend to take their fun seriously, they spend freely on sports and recreational activities. The broad range of properties available from plastics has made them part of all types of sports and recreational equipment for land, water, and airborne activities. Roller-skate wheels are now abrasion- and wear-resistant polyurethane, tennis rackets are molded from specially reinforced plastics (using glass, aramid, graphite, or other fibers), skis are laminated with plastics, and so on. 

Takami S., Luer C. and Graziadei P. (1994). Microscopic structure of the olfactory organ of the Cleamose Skate, Raja eglanteria. Anat Embryol (Berl) 190, 211-230. 

I haven t given up hope of participating in activities I used to enjoy. I never would throw away my ice skates, even though my kids always said, Nobody s gonna have an ice skating rink in Pensacola I said, One day, somebody s gonna build me one, and they did I don t know if I can physically put on the skates and skate now, but one day I m gonna ask somebody to sharpen my skates, and somebody to hold my hand, and do it ... 

If the temperature 7) is lower than the freezing temperature of the water - and it usually is - then some of the ice converts to form liquid water squeezing decreases the freezing temperature of the water. The water-on-ice beneath the skater s blade is slippery enough to allow effortless skating. 

Figure 5.9 Skaters apply an enormous pressure beneath the blades of their skates. This pressure causes solid ice to melt and form liquid water...

SAQ 5.3 A man is determined not to slip on the ice, so instead of wearing skates of area 10 cm2 he now wears snow shoes, with the underside of each sole having an extremely large area to spread his 100 kg mass (equating to 1000 N). If the area of each snow shoe is 0.5 m2, what is the depression of the freezing temperature of the ice caused by his walking over it ... 

The high surface tension of a water meniscus explains why various small insects are able to skate across the surface of a pond. 

The Hopkinton Town Council met last night to address the question of building a skate-board ramp in Wilcox Park, but the public response segment of the meeting took much longer than anticipated, and the question had to be shelved until next meeting. 

Many residents were vehemently opposed to the proposal to build a large skate boarding area in the southeast corner of the park. The proposed facilities would include a tunnel, several ramps, and a dish —all made of cement for use by skate-boarders. 

The last thing we need in this town, stated Michael Fritz of Hopkinton, is more graffiti. If we put in a skate board park, that s exactly what we ll get for our efforts. ... 

The inhibition of amino-acid transport has been regarded as the main toxic effect of mercury compounds [82], The biochemical mechanism underlying the inhibition is unclear. In unfertilized sea-urchin eggs an interaction with the amino-acid carrier was found, whereas in fertilized eggs inhibition of amino-acid transport was indirect and might result from an elevation of the Na + content of the egg caused by the inhibition of the Na+ pump [83]. The action on the diffusional process could be mediated by an effect on membrane phospholipids or on membrane proteins, or by interaction with Ca2+ which stabilizes membrane structure. Mercuric chloride in skate liver cells inhibited amino acid transport, decreased Na + /K + -ATPase (adenosinetriphosphatase) activity, impaired volume regulatory mechanisms and increased the permeability of the plasma membrane to potassium [84]. It has been suggested that... 

On the skating trail, there are a total of 29 skateboards and scooters. Skateboards have four wheels and scooters have two wheels. There are 100 wheels in total. How many scooters are there ... 

---