As the water cools at room temperature. The study of the rate of cooling water in a vessel under different conditions
The study of the rate of cooling water in the vessel
under various conditions
Executed the command:
Team number:
Yaroslavl, 2013
Brief description of research parameters
Temperature
The concept of body temperature seems simple at first glance. From everyday experience everyone knows that there are bodies hot and cold.
Experiments and observations show that the contact of two bodies, of which one we perceive as hot and the other as cold, changes occur in the physical parameters of both the first and second bodies. "The physical quantity measured by a thermometer and the same for all bodies or body parts that are in thermodynamic equilibrium with each other is called temperature." When the thermometer is brought into contact with the body under study, we see various kinds of changes: the fluid moves, the gas volume changes, etc. But soon thermodynamic equilibrium between the thermometer and the body necessarily occurs, a state in which all the quantities characterizing these bodies: their masses, volumes, pressures, and so on. From this point on, the thermometer shows not only its temperature, but also the temperature of the body under study. In everyday life, the most common method of measuring temperature with a liquid thermometer. Here, to measure the temperature, the property of liquids is used to expand when heated. To measure body temperature, the thermometer is brought into contact with it, the process of heat transfer is carried out between the body and the thermometer until thermal equilibrium is established. In order for the measurement process to not noticeably change the body temperature, the thermometer mass must be significantly less than the body mass, the temperature of which is measured.
Heat exchange
Almost all phenomena of the external world and various changes in the human body are accompanied by a change in temperature. Heat transfer phenomena accompany all of our daily life.
At the end of the 17th century, the well-known English physicist Isaac Newton came up with a hypothesis: “The rate of heat transfer between two bodies is the greater, the more their temperatures differ (by heat transfer rate we mean the change in temperature per unit time). Heat transfer always occurs in a certain direction: from bodies with a higher temperature to bodies with a lower one. Numerous observations convince us of this, even at the household level (a spoon in a glass of tea heats up, and tea cools down). When the temperature of the bodies becomes equal, the heat exchange process stops, that is, thermal equilibrium occurs.
A simple and understandable statement that heat alone moves only from bodies with a higher temperature to bodies with a lower temperature, and not vice versa, is one of the fundamental laws in physics, and is called the II law of thermodynamics, this law was formulated in the XVIIIth century by German Scientist Rudolf Clausius.
Studythe rate of cooling water in a vessel under different conditions
Hypothesis: We assume that the rate of cooling of water in a vessel depends on the layer of liquid (butter, milk) poured on the surface of the water.
purpose: Determine whether the surface layer of the oil and the surface layer of milk affect the rate of cooling water.
Tasks:
1. To study the phenomenon of cooling water.
2. Determine the dependence of the temperature of cooling water with a superficial layer of oil on time, the results recorded in the table.
3. Determine the dependence of the temperature of cooling water with the surface layer of milk on time, the results recorded in the table.
4. Build dependency graphs, analyze the results.
5. Make a conclusion about which surface layer on the water has a greater influence on the rate of cooling of water.
Equipment: laboratory glass, stopwatch, thermometer.
Experiment plan:
1. Determination of the price scale division thermometer.
2. To measure the water temperature during cooling every 2 minutes.
3. To measure the temperature during the cooling of water with a surface layer of oil every 2 minutes.
4. Perform a temperature measurement during the cooling of water with a surface layer of milk every 2 minutes.
5. Record measurement results in the table.
6. According to the table plot the graphs of the dependence of water temperature on time.
8. Analyze the results and give their rationale.
9. Make a conclusion.
Completing of the work
First, we heated the water in 3 cups to a temperature of 71.5 ° C. Then we poured vegetable oil into one of the glasses and milk into the other. The oil is distributed over the surface of the water, forming a uniform layer. Vegetable oil - a product extracted from vegetable raw materials and consisting of fatty acids and related substances. Milk mixed with water (forming an emulsion), this indicated that milk is either diluted with water and does not correspond to the fat content declared on the package, or is made from a dry product in both cases. physical properties milk change. Natural milk undiluted in water is collected in a clot and does not dissolve for some time. To determine the cooling time of liquids, we recorded the cooling temperature every 2 minutes.
Table. The study of the cooling time of liquids.
|
liquid | |||||||||||
water, t, ⁰С | |||||||||||
water with oil, t, ⁰С | |||||||||||
water with milk, t, ⁰С |
According to the table, we see that the initial conditions in all experiments were the same, but after 20 minutes of the experiment, the fluids have different temperatures, which means they have different rates of cooling of the fluid.
More clearly this is presented on the chart.
In the coordinate plane with the axes, temperature and time marked points that show the relationship between these quantities. Averaging values, held the line. The graph shows a linear dependence of the cooling water temperature on the cooling time under various conditions.
Calculate the rate of cooling water:
a) for water
0-10 min (ºС / min)
10-20 min (ºС / min)
b) for water with a surface layer of oil
0-10 min (ºС / min)
10-20 min (ºС / min)
b) for water with milk
0-10 min (ºС / min)
10-20 min (ºС / min)
As can be seen from the calculations, the water with oil cooled down the slowest. This is due to the fact that the oil layer does not allow water to intensively exchange heat with air. This means that the heat exchange of water with air slows down, the rate of cooling of water decreases, water stays hotter longer. This can be used in cooking, for example when cooking pasta, after boiling water add oil, pasta will cook faster and even will not stick together.
Water without any additives has the highest cooling rate, which means it will cool faster.
Conclusion: thus, we experimentally verified that the surface layer of the oil has a greater effect on the rate of cooling of water, the rate of cooling decreases and the water cools more slowly.
Comrade Trotsky, as you know, was convicted of the concept of a permanent world revolution. And in vain. With a confident gait, the revolution is sweeping across the planet. True, not proletarian, as the old Bolshevik dreamed, but sexy.
British teen magazine Bliss conducted a survey on the sexual life of its readers. The results of the study, which was attended by 2,000 respondents, turned out to be so entertaining that they were interested in quite serious uncles from the government of the United Kingdom.
As it turned out, almost 25% of the girls surveyed were no longer girls. The first sexual experience young British women received under very ambiguous circumstances. In 86% of cases, partners preferred to save on contraceptives (or simply did not know about their existence), and about the same number of first sexual intercourse in life occurred when young people were intoxicated. What is characteristic, most girls did not like first sex, but this did not prevent them from searching for new and new partners.
The magazine also studied the geography of the spread of early sex life. The most "advanced" were the little residents of the south-west of England and Wales - here up to 75% of girls met with carnal pleasures.
British authorities believe that if the sexual revolution cannot be stopped, at least its consequences should be minimized. Wales Children's Commissioner Peter Clark said that teens need to be given more information about sex, and should not be done in a “mentoring and paternal tone”. However, according to sex therapist Jen Berlow, the majority of girls are much more important love and understanding of loved ones than the joys of the flesh. Spreading early sex is a modern version of the problem of fathers and children, says Berlow.
It must be said that horrific, in the opinion of conservative citizens, data on teenage sex come with enviable regularity. At the end of January, it turned out that almost 100% of American high school students made love at least once in their lives. At the same time, the word “love” here looks a little out of place, since many teenagers have changed partners several times.
True, unlike their British counterparts, the American government considers it necessary to limit the sex life of its young citizens. In April last year, there was a lively debate in the United States about the fate of an emergency contraceptive that is valid for 72 hours after the start of sexual intercourse. Despite the fact that the tool is absolutely harmless, the authorities have banned it for sale to adolescents, citing the fact that teenage girls would have sex more often, knowing that unwanted pregnancy can be prevented.
They say that black tea helps black tea, and green tea helps them.
As for color, this is of course a joke. And the rest is all true. Moreover, the substances contained in tea, not only invigorate and elevate mood, but also help from many diseases.
And the eye pleases, and the heart
Even the ancient Chinese, who gave tea to the world, recommended it as a means to improve visual acuity and against rheumatism. And every year scientists discover more and more beneficial features drink. Here are some results:
Tea helps strengthen bones, supports the function of the thyroid gland.
Green tea also contributes to the secretion of gastric juice, helps appetite, digestion, regulates fat metabolism.
One of the antioxidants found in green tea helps the body burn fat and, therefore, fight excess weight.
Tea slows down the growth of cholesterol, stops atherosclerosis, reduces the risk of heart disease, destroys viruses, improves immunity, helps the body to withstand radiation.
And black and green teas can take away from the white fever, because they prevent addiction to alcohol.
The antioxidants contained in tea enhance the action of vitamin E, preserve liver cells, which prolongs life and remains active in old age. Green tea is a truly wonderful anti-aging remedy, because it is 18 times more effective than vitamin E. And the substances contained in tea protect our skin and prevent the formation of deep wrinkles.
Secrets of welding
A natural question arises: if tea is so healthy, then why does it have almost no effect on us? The answer is simple - most people do not know how to cook and use tea. However, judge for yourself how well you prepare this drink. Here are five tips that tea masters give to inexperienced teapots:
1 The main secret of healing tea is contained, of course, in the tea itself. To date, sold many varieties for every taste and pocket. But if you really want not just to quench your thirst, but to consume a drink that the ancients called the "elixir of health", then you should prefer the more sophisticated process of manual brewing to tea bags.
2 "Right" water is another important component of the drink. Chlorinated tap water definitely spoils it. Iodized water is also better not to take - it will kill the taste of tea. The Chinese generally believe that it is best to use water from a spring, which is located in the same place where tea grew. But since this condition is unattainable for us, we can assume that the drinking water, which is sold in five-liter bottles, is optimal.
3 Very much depends on the temperature of the water, which brewed tea. Recipes there are many. The optimal technology looks like this: rinse the teapot with boiling water and pour the tea leaves into it (a teaspoon per cup plus one more). All this is half filled with water, boiling and cooling to a temperature of about 70-80 degrees (boiling water completely kills all the properties of green tea). A minute later the kettle is poured to the top. For green tea, the brewing process lasts 2-3 minutes. If this tea is twisted into lumps, it should be brewed for 5-8 minutes. For black tea, brewing time is about 3-5 minutes.
4 After that, the finished tea is poured into porcelain mugs and drunk it warm, not allowing it to cool. Good green tea You can brew this way up to 4-5 times (super-quality - up to 8 times). This refers to brewing within the limits of one tea drinking, and not the next day. Experts believe that tea can bring the greatest benefit to the body only in the first 15 minutes after brewing. And after five hours of infusion, additional boiling of tea leaves or topping up boiling water into it (as many do) tea turns into not just a useless drink, but a real poison for the body. And black tea is generally better brewed only once.
5 Properly brewing tea, it is necessary and properly consumed. It is believed that you can not drink it on an empty stomach, just before a meal or immediately after it. It is best to do this half an hour before a meal or half an hour after it. Another important rule: tea should not be cold or very hot. The optimum temperature is 40-50 degrees. It is this tea that invigorates, improves mood, metabolism, clarifies the mind and sharpens the eyesight. Sometimes they wash down the medicine with tea. This, too, should not be done. The fact is that the substances contained in tea interfere with the absorption of many drugs. And, of course, you can not drink tea, which stood for many hours.
Tips
The temperature of the water for welding is easy to determine without a thermometer. To do this, you just need to have a clock and remember that water boils at a temperature of 100 degrees, as soon as you turn off the heat, the water cools down to 95 degrees, and then every minute the water in the kettle loses about five degrees.
More useful than green tea can only be green tea with lemon, say scientists who conducted a special study. It turns out that the addition of a lemon wedge increases the absorption of antioxidants three times, helping with diabetes, heart disease and even cancer.
In order for tea to retain its beneficial properties, it should be stored in a dry, airtight, opaque container. But even under such conditions at room temperature, it keeps healing properties no more than two months.