Clean plastic container (such as large margarine tub)
Icebergs are large pieces of ice that have broken off from glaciers or polar ice sheets. Composed mostly of frozen freshwater rather than frozen seawater, icebergs can float many years in the ocean before completely melting. In this experiment you are going to make a large piece of ice and use it to learn more about icebergs.
Fill a clean plastic container
three-quarters full with water. Place the plastic container of water in a freezer
and leave it there until all the water has frozen (overnight is long enough).
Remove the container of frozen water from the freezer and place it on the kitchen counter. Fill the sink nearly full with water. Remove the large piece of ice from the container. If the ice does not slip out easily, place the container in the sink of water and leave it there until the large piece of ice is loose.
Place the large piece of ice in the water. Does it sink or float? Use a ruler to measure the height of the ice sticking above the surface of the water, as shown in. Next, remove the ice from the water and place it on a towel next to the sink with the same side on top as when it was floating. Now measure the total thickness of the ice.
To calculate the percentage of ice that is submerged (below the surface of the water), first divide the height of the ice that is above the surface of the water by the total thickness of the ice. Multiply this number by 100 to get the percentage of ice floating above the surface of the water. Subtracting this percentage from 100 gives you the percentage of ice submerged. For example, if 0.8 in. (2 cm) of ice is floating above the surface of the water and the total thickness of the ice is 7.9 in. (20 cm), then 10% (0.8 / 7.9 x 100% = 10%) of the ice is floating above the surface of the water and 90% (100% - 10% = 90%) of the ice is below the surface.
Water is an unusual substance because solid water (ice) has a lower density than liquid water. For most substances, the liquid form is less dense than the solid form. Density is the ratio of the amount of a substance (mass) to the amount of space (volume) taken up by the substance. To help clarify, imagine you have 1 cup (0.24 l) each of two different liquids. Let's call them liquid A and liquid B. if liquid A has a greater density (is more dense) than liquid B, then the cup of liquid A will weigh more (have a greater mass) than that of liquid B. To think of it in another way, say you have separate samples of liquid A and liquid B that have the same weight. If liquid A is denser than liquid B, then liquid A will have a smaller volume.
A less dense substance will float on a denser substance. This is why ice floats on water. For nearly every other substance, the solid form will sink in the liquid form.
In this experiment you should find that 80% to 90% of your piece of ice is submerged. This percentage will vary depending on the amount of air trapped in the ice. The more air that is trapped, the less dense the ice and the smaller the percentage that is submerged. Ice made from water containing no air is 90% submerged in pure water.
Polar and Nonpolar liquids
Have you ever wondered
why water and oil do not mix, or how soap combats oily dirt? To learn more about
the properties of water and oil, try this experiment. (Note: this experiment
works best on a cool, dry day when the humidity is low.)
Begin by inflating a balloon and tying it closed. Turn on a sink faucet and adjust its flow to get a thin stream of water. Rub the balloon on a wool sweater or in your hair to charge the balloon. Move the charged balloon near the stream of water. What happens?
Next, use a pen to punch a small hole in the bottom of a paper cup. Hold the paper cup over the sink and add cooking oil to the cup until a thin stream of oil starts to flow from the hole in the bottom, as shown in figure A. What happens when you bring a charged balloon near the stream of oil?
Both water and oil are made up of molecules. Molecules are combinations of atoms held tightly together through chemical bonds. A good analogy for a molecule is a word, which is a combination of letters.
Within molecules are positive and negative charges. If the positive and negative charges in a molecule are not distributed evenly, one end of the molecule will be slightly negative and the other end slightly positive. Molecules with charged ends are called polar molecules. If the positive and negative charges in a molecule are distributed evenly, the molecule is nonpolar.
Rubbing the balloon on a sweater (or in your hair) causes electrons to move from the sweater and collect on the balloon, charging the balloon. Since electrons are negative charges, the balloon becomes negatively charged. You use a charged balloon in this experiment to learn whether water and oil are polar and nonpolar.
When the charged balloon is brought close to the stream of water, the stream bends toward the balloon, showing that water is polar-the positive ends of the water molecules are attracted to the negative charges on the balloon. What would happen if the balloon had a positive charge instead of a negative charge? Since the stream of oil is not affected by the charged balloon, the oil must be nonpolar.
Much of what we call dirt is made up of oil and grease. Water alone will not dissolve oil and grease because water is polar and oil and grease are nonpolar-"like dissolve like." Adding soap or detergent to the water, however, will cause the oil and grease to dissolve.
Soap and detergent molecules are unique in that they each contain a large, nonpolar tail and a smaller, polar head. The nonpolar tail combines with oil and grease while the polar head combines with water. Figure B shows how soap or detergent molecules cause oil to dissolve in water. As you can see in the figure, the nonpolar tails of many soap or detergent molecules stick into a tiny oil particle. The polar heads of the soap or detergent molecules stick out into the water, causing the oil particle to be suspended in water. The suspended oil particle can now be washed away with the water.
Two clear plastic cups
In the United States, billions of dollars are spent each year on lotions and creams to moisturize and relieve dry skin. If you read the labels on several bottles of lotion or cream, you will probably find each contains a number of ingredients, many with long scientific names. Regardless of the ingredients, the way most moisturizing lotions and creams soothe and protect skin is simple, as you will explore in this experiment.
Fill two plastic cups half full with water. Use a felt pen to label one cup A and the other cup B. Also, mark the water level on the outside of each cup. Slowly pour cooking oil into cup B until the surface of the water is just covered with oil. Place both cups in a warm place where they will not be disturbed. Each day for a week, observe how much water is in each cup. What changes do you notice in the water levels during this time? What do you think will happen to the levels after several weeks?
You should find that while the water level decreases in the cup containing only water (cup A), the water level does not significantly change in the cup with the oil layer (cup B). Water easily evaporates from cup A. The thin layer of oil floating on the water in cup B prevents the water in this cup from evaporating.
Water and oil do not mix
because their molecules are not attracted to each other. Water molecules are
polar and oil molecules are nonpolar. Like molecules attract each other. Unlike
molecules have little attraction for each other. Water and oil are unlike molecules.
Water molecules are strongly attracted to each other. This is why water is a liquid under normal conditions. To evaporate, water molecules must have enough energy to escape the attraction of their neighbors. By absorbing heat energy from the room, water in cup A constantly evaporates.
Oil molecules require more heat energy than water molecules to evaporate. Usually, cooking oil will evaporate only when it is heated to a high temperature. This is why the cooking oil does not evaporate from cup B.
Some of water molecules in cup B have enough energy to escape the attraction of their neighbors. When these molecules try to escape, they bump into oil molecules on the surface of the water. They are not able to pass through the layer of oil molecules and do not evaporate.
Moisturizing creams and lotions, which typically contain mineral oil or petroleum jelly, work in much the same way as the layer of oil on the water in this experiment. They help prevent water from evaporating from the skin.
Healthy skin contains about 10% moisture. When skin has a lower moisture content, it becomes dry and flaky. Skin protects itself from loss of water by secreting an oil that forms a film on the skin. This natural skin oil can be removed by exposure to sun and wind as well as by washing. Moisturizing creams and lotions replace the natural oil in the skin and prevent or slow the evaporation of water from the skin.
Water drops riding on steam
In this experiment you will
observe what happens when a drop of water comes in contact with a hot metal
Turn a heater to a high setting for about 10 minutes to allow it to become hot. Be careful not to touch the heater. Add a drop of water carefully to the heater. Do not add more than a drop of water at a time to the heater. Add more drops of water and observe their behavior. Turn off the heater and allow it to cool.
The boiling point of water,
212°F (1OO°C), is the temperature at which liquid water is changed to
water vapor (steam). Since the temperature of the heater is probably more than
400°F (204°C), you might expect that a drop of water would instantly
change to steam. Instead, the drop lasts a long time in the heater. You probably
observe that the drop of water placed on the heater seems to skate around in
the heater as it makes a sizzling sound. This surprising behavior of water drops
on a hot surface is called the Leidenfrost effect.
As the drop of water comes in contact with the metal surface, the outer layer of the drop begins to vaporize (change from a liquid to a gas). This water vapor provides a layer of gas upon which the water drop floats. This gas also provides a barrier to the flow of heat from the heater to the cooler liquid water. As a result, the water drop does not immediately vaporize but instead may take several minutes to change completely to water vapor. The liquid changes to steam, and the drop gradually disappears.
In the Leidenfrost effect, only that part of the drop that touches the hot surface changes to steam. Heat does not flow through gas as well as it does through water. Therefore, the drop is insulated from the hot surface by the steam coming off the drop.
Have you ever seen pictures or movies of people walking across glowing hot coals? (Do not try to touch or walk on hot coals.) How do firewalkers keep their feet from getting burned? Let's discuss several reasons: First, the layer of coals has a high temperature, but the red-hot layer is quite thin. Therefore the total amount of heat energy along the top of a suitable bed of coals is not high. Second, tissue in feet is mostly water, and water can store a lot of heat energy. Therefore, a firewalker's feet can absorb a certain amount of heat without getting burned. Third, the Leidenfrost effect helps insulate the firewalker's feet. Perspiration or moisture on the feet changes to steam and absorbs energy. As you know from your experiment, this steam can act like a layer of insulation. This gas underneath helps protect feet from the effects of the heat. However, even though we understand the science of firewalking, it should only be done by those specially trained in this unique activity.
In this experiment you will explore why water wets (spreads out on) or does not wet a surface.
Place a sheet of wax paper about the size of a piece of notebook paper on a flat surface. Use a spoon to add about 1 teaspoon (5 ml) of water to the wax paper to make a blob of water about the size of a quarter. Slightly lift the edges of the paper and move the blob of water around on the surface of the wax paper. Observe how the water moves across the surface. Touch the wax paper where the water has been. Does the wax paper feel wet?
Now, move the blob of water to the center of the wax paper. Add one drop of dishwashing liquid to the center of the water blob. What happens?
Lift the edges of the wax paper to make the water move across the surface. Touch a spot where the water has been. How does it feel?
You should find that the water blob moves freely across the surface of the wax paper without wetting it. The water molecules in the blob pull together to stay in the shape of a drop. The wax paper does not feel wet even where the large drop of water has passed across the surface.
After the drop of dishwashing soap is added to the water, the behavior of the water should be much different. The soapy water mixture should spread out across the surface rather than staying in a small blob. When you touch the surface over which the water has passed, it probably feels wet. The water did not wet the wax surface. However, the soapy water does.
Water molecules are polar, which means that they each have a positive and a negative side. Molecules of the wax on wax paper are nonpolar, which means that they do not have a positive and negative side. Polar molecules will mix with other polar molecules, just as nonpolar molecules will mix with other nonpolar molecules. However, polar molecules do not mix with nonpolar molecules. The water and wax paper do not mix. The water molecules stay together in the form of a bead or large drop to minimize their contact with the wax paper. They do not spread out on the surface.
Soap molecules are unique because they each have a polar and a nonpolar part. A soap molecule has a long part that is like a wax molecule and is called a tail. It also has a short part that is like a water molecule and is called a head. The head of a soap molecule is polar, while the tail of it is nonpolar.
When soap is added to water, it causes the water to wet the surface of the wax paper. The heads of the soap molecules attract, or mix with, the water. The tails of the soap molecules are attracted to, or mix with, the wax. Since the soap is attracted to both the water and the wax, it causes the water to spread out across the surface of the wax paper.
Scientists have made a drop of water move uphill against gravity by making one side of a surface underneath the drop polar and the other side nonpolar. The drop of water moves toward the polar side even if it is uphill from the water.
Sometimes we want to make surfaces that cannot be wet with water. For example, car wax is used to make a nonpolar surface on which water will bead up rather than wet the surface. Glass is sometimes coated with a nonpolar substance so water will not stick to the surface and the glass will not "fog up" (become covered with tiny droplets of water).
Sometimes we want to change
liquids so that they can be more easily wet by water. Spills of oil into the
ocean can damage the environment and harm living things. One of the ways used
to clean up oil spills is to add surfactants (soaplike molecules) to the oil.
A surfactant molecule has a polar and nonpolar part, and thus a surfactant can
help the oil mix with the water so it does not wash up on beaches and kill animals.
Do you think you can bend
light? In this experiment you will try to use water to make light go around
Place an empty plastic pitcher in a sink under a water faucet so that you can add water to the pitcher without moving it. Put a nickel in the bottom of the pitcher. Move the nickel until it is touching the side of the pitcher toward the front of the sink. Begin with your head directly over the pitcher so you can see the nickel inside the pitcher. Now, slowly move your head back, away from the sink, until the nickel completely disappears. You must stay very still and keep your head in exactly the same place for the rest of this experiment.
While holding your head steady, turn on the faucet to allow water to flow. As the water fills the pitcher, continue to look at the bottom of the pitcher. When the water has nearly filled the pitcher, turn off the faucet to stop the water. Do not move your head. Where is the nickel? Can you see it?
You probably observed that as water was added to the pitcher, the nickel seemed to move. The nickel could not be seen at all when the pitcher was empty and the side of the pitcher blocked your view. However, when the pitcher was filled with water, you should have been able to see the nickel even though you had not moved your head. Can you explain this change?
In order for you to see the nickel in the bottom of the pitcher, light striking the nickel must reach your eye. Light normally travels in a straight path, and when the pitcher is empty the light reflected off the nickel travels straight to your eyes. When you move your head back, the side of the pitcher blocks the light and you cannot see the nickel. However, when water is added to the pitcher, the light no longer travels in a straight line, but is bent.
Light waves are bent when they travel from water into air or air into water. Refraction, the bending of light, occurs whenever light goes from one substance into another. The light is bent when it goes from air to water because light waves travel more slowly in water than in air. Two substances in which light travels at different speeds will cause refraction if the light goes from one substance to the other at an angle (not straight).
Scientists use the index
of refraction as a measure of how much light bends when it passes from one substance
into another. The index of refraction is the ratio of the speed of light in
a vacuum to the speed of light in specific substance. A device called a refractometer
can measure this extent of bending. Measuring the index of refraction with a
refractometer is one-way scientists identify unknown liquids or determine the
amount of liquids in a mixture.
When light passes from air into glass and then out of the glass, it can be bent. Different colors of light are not bent by the same amount, and so the effect of this bending, or refraction, is to spread white light into the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet.
Absorbing microwave energy
Two microwave-safe containers
Have you ever wondered how a microwave oven cooks food? In this experiment you will compare the microwave energy absorbed by sugar and water and learn more about cooking with microwave ovens.
Place 1-cup (0.24 l) of sugar in a microwave-safe container. Place I cup (0.24 l) of water in a second microwave-safe container. Never put metal objects into a microwave oven because they could damage the microwave oven when it is operating. Put both containers into a microwave oven and heat on full power for two minutes. Use an oven mitt to remove both containers and place them on a countertop.
Place a cooking thermometer into the container with the sugar. Leave the thermometer in the sugar for about 20 seconds and then check the temperature. What is the temperature of the sugar? Place the cooking thermometer in the second container and measure the temperature of the water. What is the temperature of the water?
You should find after heating
in a microwave oven that the water is warm while the sugar remains cool. The
temperature of the water may be 150°F (66°C) or higher. However, the
thermometer in the sugar will probably not show any change, so the sugar has
remained close to room temperature.
Microwaves are a type of
electromagnetic energy. Microwave ovens use this energy to cook foods. The microwaves
are absorbed by water molecules in food and cause the water molecules to rotate
more rapidly The extra energy of these more rapidly rotating water molecules
spreads out and causes other molecules to move more rapidly This causes the
food to get warm and cook. Since the dry sugar does not contain water molecules,
it does not absorb the microwave energy.
Microwaves go through glass and paper without heating them. Metal objects reflect microwaves and will damage microwave ovens if placed in them. The walls of microwave ovens are metal to help reflect the microwaves back to the food to be cooked.
A special electronic tube
called a magnetron is used to convert the energy of electricity to microwave
energy. The microwaves are scattered into the microwave oven by a stirrer that
has moving metal blades like a fan. The advantage of the microwave cooking is
that it is a quicker and more energy efficient that conventional electric cooking.
In conventional electric cooking an electric current passes through a coil of
wire that gets hot because of the resistance of the wire to the current flow.
The amount of heat generated in a microwave oven depends on the amount of water present in the flood. In general, the more water, the faster the food cooks. Other liquids such as oil may absorb microwaves, but not as efficiently as water does.
Electromagnetic waves may pass through matter or may absorbed by it. X-rays, used to take skeleton pictures, pass through air and paper but are absorbed by water and reflected by metal. Light passes through air and water but is blocked by paper and metal.
Copyright © team C0126220(ThinkQuest 2001). All rights reserved.