Science 8 REEEEEEEEEEEEEEEEE
96.Why does the boiling temperature of water decrease when the water is under reduced pressure, such as at a higher altitude?
Less presure holding the water particles together
103.How do the temperature at which a particular metal melts and the temperature at which it freezes compare?
The melting and freezing temperatures are the same.
126.A piece of metal and an equal mass of wood are both removed from a hot oven at equal temperatures and dropped onto blocks of ice. The wood has a higher specific heat capacity than the metal. Which melts more ice before cooling to 0°C?
Wood: has higher specifc heat
116.What is the source of energy that keeps the dunking bird in Figure 7.28 operating?
energy in the room keeps it moving. Hotter= work better. water is eveaporating of ht head. This makes ether inside condense. This decreases prressure which makes fluid go up the tube
62.Wood is a better insulator than glass. Yet fiberglass is commonly used as an insulator in wooden buildings. Explain.
fiber glass is 95% air which makes it a good insulator.
63.Visit a snow
covered cemetery and note that the snow does not slope upward against the gravestones but, instead, forms depressions around them, as shown. What is your explanation for this?-Heat from the relatively warm ground is conducted by the gravestone to melt the snow in contact with the gravestone. Likewise for trees or any materials that are better conductors of heat than snow, and that extend into the ground.
105.What role does antifreeze play in preventing the freezing of water?
has a lower freezing point than water, so it mixes with it and prevents it from freezing at it's normal 32 degrees
66.Many tongues have been injured by licking a piece of metal on a very cold day. Why would little harm result if one licked a piece of wood on the same day?
water in your saliva will freeze and stick your tongue on the pole
98.Your inventor friend proposes a design for cookware that allows boiling to take place below 100°C so that food can be cooked with less energy. Comment on this idea.
water is held together by pressure in the atmosphere. Take away lotta thermal energy in a vacuum or add lotta thermal energy to make it boil. If lower temperature, it would take twice as long to cook it. Less pressure, less temperature.
104.Discuss why halffrozen fruit punch is always sweeter than completely melted fruit punch.-
water is in form of ice crystals. Only taste syrup
102.Distinguish between melting and freezing in terms of molecular speeds.
when melting, movement increased. When freezing molecules are still and in a fixed position.
94.Double pane windows have nitrogen gas or very dry air between the panes. Why is using ordinary air between the panes a poor idea?-
when window cooled, condesnation happens. moisture is a conductor, so it will allow more enrgy through it.
120.Why can you drink a cup of boiling hot tea atop a high mountain without any danger of burning your lips? What if you did this in a mine shaft below sea level?-
120. When you drink tea from this height, it is high above the ground and thus in an area of lower pressure. This means there is less force pushing the thermal energy particles down. This causes them to spread out more freely, which makes your drink colder. In a deep mine shaft onthe other hand, the tea will be hotter than usual because there is more pressure pushing the thermal energy partiels down, which compresses them and makes them more effectively hotter.
70.Snowmaking machines used at ski areas blow a mixture of compressed air and water through a nozzle. The temperature of the mixture may initially be well above the freezing temperature of water, yet crystals of snow are formed as the mixture is ejected from the nozzle. Explain how this happens.
70. This is because when this mixture goes through the small nozzle, it cools. This is because an object will cool when it expands. In this case, when the mixture is in a wide open space and can't expand, it is warm, but when it goes through the nozzle and then expands from there, it is cool.
74.If everything radiates, why doesn't everything zoom downward in temperature?
74. Everything doesn't zoom down in temperature because everything is also an absorber, and as we learned before, hot goes to cold, so that radiated energy goes to a colder substance and is absorbed by it. Basically, it is like money, there is a limited amount of it, but it is traded around.
76.Using as a guide the rule that a good absorber of radiation is a good radiator and the rule that a good reflector is a poor absorber, state a rule relating the reflection and radiation properties of a surface.
76. A good reflector of radiation is a poor radiator and therefore a poor absorber. This is because it will reflect absorbing radiant energy and this will not make it have much energy to radiate.
78.In terms of physics, why do restaurants serve baked potatoes wrapped in aluminum foil?
78. Aluminum foil is a good reflector so it won't absorb much heat emitted by the potato which will cause the heat to stay around inside the foil. This will keep the baked potato warm when it reaches the restaurant patron. Delicious!
80.Which decreases in temperature more rapidly, a white hot poker or a red-hot poker? Or do they cool at the same rate?-
80. A white hot poker decreases more rapidly because of Newton's LAw of Cooling which states that an object cools at a rate that depends on the difference in temperature between the object and the environment around it. In this case, a white hot poker is hotter than a red hot one which in turn creates a bigger difference in temperature which causes the white hot poker to cool faster.
87.You can determine wind direction by wetting your finger and holding it up in the air. Explain.
87: Where more water evaporates off your finger, the wind is blowing that way
88.Why does a dog pant when it is hot?
88. A dog pants when it is hot because it does not have sweat glands to cool it, so it cools off by panting which triggers evaporation, which is a cooling process, to cool off the dog.
89.Give two reasons why pouring a cup of hot coffee into a saucer results in faster cooling?
9: more surface area (more room for evaporation). less mass (less thermal transfer)
91.Why does wrapping a bottled beverage in a wet cloth at a picnic often produce a cooler bottle than placing the bottle in a bucket of cold water?
A bottle wrapped in wet cloth will cool by the evaporation of liquid from the cloth. As evaporation progresses, the average temperature of the liquid left behind in the cloth can easily drop below the temperature of the cool water that wet initially. So to cool a bottled beverage at a picnic, wet a piece of cloth in a bucket of cool water, then wrap it around the bottle. As evaporation progresses, the temperature of the water in the cloth drops, and cools the bottle to a temperature below that of the water in the bucket.
93.Erik Wong crunches an aluminum soft drink can on page 180. Is the can sucked in by the partial vacuum created, or pushed inward by atmospheric pressure? Or both?-
A vacuum is a condition of nothingness, which cannot suck the can inward. The vacuum, even partial, allows the outside atmosphere to exert a net force on the walls of the can, which causes the sudden crunch. So it is not "both."
111.Your friend says that more thermal energy is needed to increase a gram of water from absolute zero to its boiling point than is needed to boil the water once it reaches 100°C. Do you agree or disagree?
Agree, for along the way from absolute zero to boiling water, you encounter 334 J in changing phase from ice to water, but a whopping 2256 J to change the water to steam. The energies in raising ice and water temperatures along the way aren't enough to overcome this difference
92.A friend says that the reason why you feel uncomfortable in muggy weather is that water molecules in the air are giving up energy while bombarding you. Do you agree or disagree with your friend?
Agree. water loses energy by condensing on your skin condensation warms your skin. water loses energy and that energy transfers to your skin. also lesser rate of evaporation..
69.When you blow air onto your hand from your wide open mouth, your hand is warmed. Why is your hand cooled if you pucker your lips when blowing?-
Air cools when it expands. Expansion is minimal when blown from your wide-open mouth, but is greater when exiting the smaller opening with puckered lips. The cooled breath cools your hand.
72.The source of the heat of volcanoes and natural hot springs is trace amounts of radioactive minerals in common rock in Earth's interior. Why isn't the same kind of rock at Earth's surface warm to the touch?
All that radiant energy is held in by the Earth's crust like a cooler that is made to keep something warm. Anything can block radiation. When it's on the surface, it emits all tat energy and now its not warm
67.How does buoyancy play a role in the rising of a parcel of warm air?
Any parcel of air displaces its own volume of surrounding air. If the parcel is warmed it expands and becomes less dense than the surrounding air. Since it displaces a greater weight of air than its own weight, it is buoyed upward.
121.Hydrothermal vents are openings in the ocean floor that discharge water at temperatures far exceeding 100°C. Discuss why this water is not boiling.
As in a pressure cooker, the great pressure on the ocean floor prevents boiling of water at temperatures exceeding 100°C.
130.The snow covered mailboxes raise a question: What explains why the light-colored ones are snow covered, while the black ones are free of snow?-
Black ones emit heat better than white
95.Boiling can be brought about by increasing the temperature of water. How can boiling be brought about without increasing water temperature?
Boiling can be brought about by reducing the air pressure on the water.
114.Friends in your discussion group say that when you touch a piece of ice, cold "flows" from the ice to your hand, which is why your hand is cooled. What is your more enlightened response?
Cold does not flow from your ice to your hand. Thermal energy rather transfers from your hand to the ice cube. Hence why the ice cube melts, because the thermal energy it gained is melting it.
99.When boiling spaghetti, is your cooking time reduced if the water is vigorously boiling instead of gently boiling?
Cooking time will be no different for vigorously boiling water and gently boiling water, for both have the same temperature. The reason spaghetti is cooked in vigorously boiling water is simply to ensure the spaghetti doesn't stick to itself and the pot. For fuel economy, stir your spaghetti in gently boiling water.
75.What is the name given to radiant energy emitted by Earth? How does it differ from radiation emitted by the Sun?
Energy emitted by Earth is called terrestrial radiation. It differs only in frequency from radiation emitted by the Sun. Most radiation emitted by the Sun is of higher frequency.
77.You enter a crowded and chilly classroom early in the morning on a cold winter day. Before the end of the hour, the room temperature increases to a comfortable level, even if heat is not provided by the school heating system. Why the difference?
Every student radiates about the same amount of heat as a 100-W incandescent bulb. So heat radiated by you and your classmates increases the temperature of the room.
110.For water, which has the higher value: heat of fusion or heat of vaporization?
Heat of vaporaization 54
61.Which will cool your finger faster, touching a nail stuck in ice or touching the surface of the ice? Explain.
Heat will conduct from your warm finger to the cold ice either way, but faster through the nail because it is more conducting than snow.
83.If the composition of the atmosphere were changed so that it permitted a greater amount of terrestrial radiation to escape, what effect would this have on Earth's climate?
If more terrestrial radiation in the atmosphere escaped, Earth's climate would be cooler.
117.How do the average kinetic energies of hydrogen and oxygen gases compare when these two gases are mixed at the same temperature? How do the average speeds of their molecules compare? Discuss how mass is the crux of these questions.
If they have the same temperature, then by definition, they have the same average kinetic energies per molecule. But the hydrogen, with less mass, has the higher speed (½mV2 = ½Mv2, where V > v).
118.In a mixture of U 238 and U-235 isotopes, which atoms have the greater average speed? How would this affect diffusion through a porous membrane of otherwise identical gases made from these isotopes? Link this to the previous question.-
If they have the same temperature, then by definition, they have the same average kinetic energies per molecule. But the hydrogen, with less mass, has the higher speed (½mV2 = ½Mv2, where V > v).
115.If all the molecules in a liquid had the same speed, and some were able to evaporate, would the remaining liquid be cooled? Explain.
In this hypothetical case evaporation would not cool the remaining liquid because the energy of exiting molecules would be no different than the energy of molecules left behind. Although thermal energy of the liquid would decrease with evaporation, energy per molecule would not change. No temperature change of the liquid would occur. (The surrounding air, on the other hand, would be cooled in this hypothetical case. Molecules flying away from the liquid surface would be slowed by the attractive force of the liquid acting on them.)
79.Why isn't it important to convert temperatures to the Kelvin scale when we use Newton's law of cooling?
Kelvins and Celsius degrees are the same size. Although ratios of these two scales will produce very different results, differences in kelvins and differences in Celsius degrees will be the same. Since Newton's law of cooling involves temperature differences, either scale may be used.
127.Earth scientists are considering a means of inducing clouds to be a brighter white. What effect would this have on Earth's climate?
More solar energy would be reflected into space, cooling Earth's surface beneath. (Whitening clouds is a consideration in offsetting the warming by excess carbon dioxide.)
112.Wrap part of a fur coat around a thermometer. Discuss whether or not the temperature rises.
NO CHANGE. A coat is an insulator and slows the transfer of thermal energy from one thing to another. So if thermometer is in thermal equilubiruj with oustide envirment, it won't change temp with coat around it. When wearing coat outside when hot, your body creates tehrmal energy continously and you can't release it so you bburn up
109.Air conditioning units contain no water whatsoever, yet it is common to see water dripping from operating outdoor air conditioners on homes on a hot day. Explain.-
No water leaks from inside the unit, for the dripping water is water vapor in the air that has condensed on the cold coolant tubes.
119.A number of objects at different temperatures placed in a closed room share radiant energy and ultimately come to the same temperature. Would this thermal equilibrium be possible if good absorbers were poor emitters and poor absorbers were good emitters? Defend your answer.
No. If good absorbers were not also good emitters, then thermal equilibrium would not be possible. If a good absorber only absorbed, then its temperature would climb above that of poorer absorbers in the vicinity. And if poor absorbers were good emitters, their temperatures would fall below that of better absorbers.
82.Why is a water based white solution (whitewash) sometimes applied to the glass of florists' greenhouses? Would you expect this practice to be more prevalent in the winter or in the summer?-
Summer. This solution helps reflect radiation. Reflects the heat away from the greenhouse so the plants don't overheat.
81.Which will warm by 15°C quicker in a 100°C oven: a 10°C piece of pie or a 20°C piece of pie?
The 10°C piece of pie will warm faster because, in accord with Newton's law of cooling, ΔT (100°C − 10°C) with its surroundings is greater than for the 20°C piece of pie.
101.In the power plant of a nuclear submarine, the temperature of the water in the reactor is above 100°C. How is this possible?
The boiling point of water is higher in a nuclear reactor because of increased pressure. The reactor behaves like a pressure cooker.
113.What is the principal reason why a feather quilt is so warm on a cold winter night?
The feather quilt is an excellent insulator (poor conductor due to trapped air), which slows the transfer of heat from your body to the surroundings.
73.What does the formula f ~ T tell us about what radiates and what doesn't?
The formula tells us that any object with any temperature is continually emitting radiant energy.
71.From a position near an incandescent lamp, turn it on and off quickly. While it is briefly on you feel its heat, but when you touch the bulb, you find that it is not hot. Explain why you felt heat from the lamp.
The heat you received was from radiation, which travels at the speed of light. Heating the glass, however, is a longer process.
123.If you wish to save fuel and you're going to leave your warm house for half an hour or so on a very cold day, should you turn your thermostat down a few degrees, turn it off altogether, or let it remain at your preferred room temperature? This question should elicit much discussion!
Turn your heater off altogether to save fuel. When it is cold outside, your house is constantly losing heat. How much is lost depends on the insulation and the inside and outside temperature differences (Newton's law of cooling). Keeping ΔT high consumes more fuel. To consume less fuel, keep ΔT low and turn your heater off altogether. Will more fuel be required to reheat the house when you return than would have been required to keep it warm while you were away? Not at all. When you return, you are replacing heat lost by the house at an average temperature below the normal setting, but if you had left the heater on, it would have supplied more heat, enough to make up for heat lost by the house at its normal, higher temperature setting. (Perhaps your instructor will demonstrate this with the analogy of leaking water buckets.)
85.What does the planet Venus have to do with Earth's greenhouse effect?
Venus is thought to have been Earthlike in the past, with a tipping point of carbon dioxide buildup that makes it now uninhabitable, which serves as a warning for Earth.
129.Why does spraying fruit trees with water before a frost help protect the fruit from freezing?
Water can emit a lot of heat. Aborsbs heat. Good absorber is a good emitter, and also the fact that the coating of ice acts as an insulating blanket. Every gram of water that freezes releases 80 calories, much of it to the fruit; the thin layer of ice then acts as an insulating blanket against further loss of heat.
128.Why does placing a tub of water in a farmer's canning cellar help prevent canned food from freezing in cold winters?
Water can emit a lot of heat. Aborsbs heat. Good absorber is a good emitter.
125.Place a jar of water on a small stand on the bottom of a saucepan of water. Then the bottom of the jar is positioned above the bottom of the pan. When the pan is put on a stove, the water in the pan boils, but the water in the jar does not. Why?
When the saucepan and jar both reach the boiling temperature, further heat does not enter the jar because it is in thermal equilibrium with the surrounding 100°C water in the saucepan. This is the principle of the "double boiler."
64.Wood has a very low conductivity. Does it still have a low conductivity if it is very hot that is, in the stage of smoldering red hot coals? Could you safely walk across a bed of red hot wooden coals with bare feet? Although the coals are hot, does much heat conduct from them to your feet if you step quickly? Could you do the same on pieces of red hot iron? Explain. (CAUTION: Coals can stick to your feet, so OUCHdon't try this!)
Yes because when something is a good insulator, it is a good absorber as well and in this case, it absorbs plenty of heat to make it very hot. You could safely walk barefoot across a bed of hot coals because they are good insulators so they will not transfer much heat to your feet. If you were to step quickly across these coals, you will burn yourself because your feet will make thermal energy which will heat them up and in turn begin absorbing more energy to keep yourself moving. Iron is a very good conductor
107.When can you withdraw heat from a substance without lowering its temperature? Give an example.
You can withdraw heat without lowering temperature when the substance is undergoing a change of phase. Small amounts of heat taken from 0°C water, or from 100°C steam, for example, doesn't lower temperature.
97.Room temperature water boils spontaneously in a vacuum on the Moon, for example. Could you cook an egg in this boiling water? Explain-
You could not cook food in low-temperature water that is boiling by virtue of reduced pressure. Food is cooked by the high temperature that food is subjected to, not by the bubbling of the surrounding water. For example, put room-temperature water in a vacuum and it will boil. But this doesn't mean the water will transfer more thermal energy to an egg than before boiling—an egg in this boiling water won't cook at all!
86.Alcohol evaporates more rapidly than water at the same temperature. Which produces more cooling: alcohol or the same amount of water on your skin?
Your hand gives alcohol more energy to evaporate at this faster rater, thus your hand is cooler when alcohol evaporates off your hand compared to water
100.Why does putting a lid over a pot of water on a stove shorten the time needed for the water to come to a boil, whereas after the water boils, the use of the lid only slightly shortens the cooking time?
add thermal energy to bottom, lose at the top. When a lid is on, it keeps more thermal energy from escaping. Temperature doesn't change when boiling happens.
122.Suppose that at a restaurant, you are served coffee before you are ready to drink it. In order that it be as hot as possible when you are ready for it, would you be wiser to add cream to it right away or to add cream just before you are ready to drink it? This question should elicit much discussion!
adding the creamer right awayu because it makes stghe cofee whiter which makes it a worse emitter because black is a good emitter and whit is less. and get to desired temp fast
106.When can you add heat to a substance without raising its temperature? Give an example.
as it melts, it doesn't go up. As it boils is doesn't go up.
90.Porous canvas bags filled with water are used by travelers in hot weather. When the bags are slung on the outside of a fast moving car, the water inside the bags is cooled considerably. Explain.-
bag allows it to be wet which causes water outside to be evaporated and cooled
108.What does an air conditioner have in common with a refrigerator?
both suck out thermal energy from stuff
124.If you wish to save fuel and you're going to leave your cool house for half an hour or so on a very hot day, should you turn your air
conditioning thermostat up a bit, turn it off altogether, or let it remain at your preferred room temperature? This question should elicit much discussion!-Turn off. Heat raises to baseline temp. Not much replacement. No constantr enegry add needed
68.When air is rapidly compressed, why does its temperature increase?
increasing temperature expand the air but if you stop increase the temperature, the air will start to compress again
60.Between the act of standing barefoot on top of an igloo and being inside, when does snow act as a conductor and when does it act as an insulator?
snow has air in it and air is a poor conductor which makes snow a good insulator and a poor conductor. snow is a good conductor when you are touching it and not a good one when you are not touching it
65.What is the purpose of the copper or aluminum layer on the bottom of a stainless
steel pot?- Copper and aluminum are better conductors than stainless steel, and therefore transfers heat more quickly to the pot's interior.
