Water

Dictionary Definition

A clear, colorless, odorless, and tasteless liquid, essential for most plant and animal life and most widely used of all solvents.

Statistics

Freezing Point: 0 degrees Celsius (32 degrees Fahrenheit)
Boiling Point: 100 degrees Celsius (212 degrees Fahrenheit)
Specific Gravity (at 4 degrees Celsius): 1.000
Weight per Gallon (at 15 degrees Celsius): 8.337 pounds (3.772 kilograms)

Cycle

Water is always circulating between the sea and the sky in a cycle called the water cycle. Water we use usually ends up in rivers, lakes, or the sea, where it evaporates in the heat of the sun to fill the lower layers of the atmosphere with water vapor. Some of this vapor is carried by the rising air currents until it cools and condenses into clouds of water droplets and ice. Then, once the drops grow big enough and the clouds grow cold enough, the water falls to the Earth's surface as rain and snow. Some of this runs back to the sea, and some is trapped in reservoirs and supply taps to let the cycle continue.

Cleaning

Explanation

If you draw a bucket of water from a pond or the bed of a stream and let it settle, you can see how dirty the untreated water is. This isn't water that you would want to drink!

But, people need a lot of water. New York City, for example, consumes 1.8 billion gallons (7 billion liters) of water each day. It would take seventeen days to fill the city's twenty-one reservoirs at a quarter of a million gallons a second (1 million liters). All this water is drawn from rivers, lakes, and wells, and pumped to the inhabitants through pipes. But water always has to be cleaned. So it is usually pumped into reservoirs first, where solid debris can settle at the bottom. Then it heads off to treatment plants where it is sieved to remove algae and sent through gravel and sand to filter out other dirt. After that it is treated with chlorine to kill off germs, then pumped to the main supply pipes or storage reservoirs.

As you can see, there are many processes that water goes through from the river to you. Companies that filter the water must get it clean enough, and healthy enough, for you to drink it. They filter it to get rid of the dirt, chlorinate it to get rid of the germs, and then send it to you to drink. When you're done with the water, it goes down the drain, back into the rivers, and eventually back into the filters. Below is an experiment you can do to see some of the methods used to filter water.

However, the water you produce still won't be clean enough for you to drink.

Experiment #1: Filtering

What You'll Need:

cupful of coarsely broken charcoal
cupful of rinsed sand
cupful of washed gravel
6 in (15 cm) clay flowerpot
coffee filter paper
jug of pond water
fine sieve
large dish

Preparation:

Wash the clay pot and let it dry.

Directions:

Line the pot with filter paper and place it in a dish.
Fill the pot one-third full with charcoal.
Rinse the sand in a sieve under running water.
While the sand is still wet, add it to fill the pot another 1/3 full.
Wash the gravel and use it to fill the pot.
Put the sieve over the pot and gently pour in the pond water (keep holding the sieve) in a steady stream so you don't disturb the layers.
Your cleaned water will be in the dish.

What's Happening?

The large debris is caught by the sieve, the gravel traps the other large debris not caught by the sieve, the sand traps the smaller pieces of dirt, and the charcoal and paper catch the finest particles. Compare what you started with and the end result in the dish and you can see just how much cleaner it is. However, it still isn't clean enough to drink.

Power

Explanation

Water has great power, and once a heavy mass of water is moving, it is hard to stop. Sometimes the power of water comes from gravity pulling it down the hill. Other times, it has to do with the water's depth that adds pressure through the weight of the water.

Since a liquid can't be squeezed, it can be used to transmit force through pipes. The experiment below demonstrates how hydraulic (liquid) systems, like car brakes, works. The water is transferred from one place to another because the power pushes the water to fill up the space at the other end.

Experiment #2: Hydraulic

What You'll Need:

two icing syringes
plastic tubing
water

Directions:

Fill one syringe with water, and then insert the nozzle into the plastic tube.
Fill the tube with water by pressing the syringe. Hold up the tube so the water doesn't fall out.
Half-fill the second syringe with water, and attach it to the other end of the tube. Make sure there aren't any air bubbles inside the tube or syringes.
Press one syringe and you will see the plunger on the other syringe move out.
If you can, try the experiment again with two different sizes of syringes.

What's Happening?

The plunger you push in causes the other to push out because the force has been transmitted through the tube. Everything has water except the empty half of one of the syringes, so water that is pushed out of the space in one finds room in the other syringe. When you try the same experiment with two different sized syringes, the smaller plunger moves farther but with less force, while the larger plunger moves less distance but with more force.

Pressure

Explanation

One of the ways that water gets its power is through the depth of the water that pushes down. The further you go down, the more pressure there is because there is more water to press down. The experiment below demonstrates how the bottom has more pressure than the top.

Experiment #3: Water Pressure

What You'll Need:

two quart plastic drinking bottle
dish
nail
water
scissors

Directions:

Cut off the top of the drinking bottle with scissors and make holes with a nail at four different levels.
Place the bottle in the dish and cover the holes with your fingers.
Have a friend fill the bottle with water.
When the bottle is full, take away your fingers.
Watch the lower holes shoot out longer streams of water.

What's Happening?

The holes that are farther down have more water pressure. There is more water on top of the bottom holes, pushing down, than there is on top of the highest hole. The extra pressure that comes with the depth causes the water to jet out in longer streams. Water has the power to push, and there is more force when there is more water.

Raising

Explanation

Water can be channeled easily through pipes and aqueducts as long it is flowing downward. However, it sometimes needs to be raised, so we employ siphons and pumps to help us transport the water. Siphons raise the water by using the pressure of the water itself. With pumps, you provide an external force. Hand pumps have been used since before 300 B.C. The simplest old-fashioned pumps were for drawing up water from underground. They would lift a little water at a time with a plunger or piston moved up and down by a hand level. They use air pressure to push water in behind the plunger, so can only lift about 28 ft (9 m). A siphon is also very simple to use, and is often used today for emptying tropical fish tanks. It is gentle and removes the water without disturbing anything. Use the experiment below to make your own siphon.

Experiment #4: Siphon

What You'll Need:

two large glass bottles
a piece of plastic tubing

Directions:

Place both bottles on a level surface.
Fill one of the bottles 3/4 full with water.
Place the tube in the filled bottle and water up the tube until it is filled.
When the tube is full, raise it above eye level.
Stop sucking and immediately put your thumb over the end of the tube so no water can get out.
Place the end of the tube in the empty bottle.
Take away your thumb and watch what happens.

What's Happening?

When you put the tube into the empty bottle, water flows from the upper to the lower bottle. Water pressure drives it down the tube in the same way that jets of water shoot from holes in experiment number three. The water pressure pushes to get the water level the same in both bottles. Since one is higher then the other, the higher one needs less water and the lower one needs more water to equalize the water level.

Density

Explanation

Some things float in water, and some things don't. The concept that explains this is density. Things that are lighter than water are also less dense, and they float on it. Things that are heavier are also more dense and they sink. When any object is submerged, its weight pushes it down. But the water pushes back upward with a force equal to the water displaced by the object. If the object is less dense than water, the upthrust makes it float, but if it is more dense it will sink. The same idea works with different liquids, as long as they don't mix. A light liquid will float on top of a heavy one.

Water even varies in density, so ships can float at different heights in different water. The change in density of water has to do with the contents. For example, salt water makes a ship float higher than fresh water. Also, they will float higher in cold seas than in warm seas, because cold water is more dense. There is a line marked on boats, called the Plimsoll line, that shows the maximum safe level the ship can be loaded to that will be safe for all kinds of water. You can measure the density of a liquid using a hydrometer. Look at the experiment below.

Experiment #5: Hydrometer

What You'll Need:

three glass beaker
drinking straw
modeling clay
water
salt
cooking oil
marking pen

Directions:

Stick a blob of modeling clay to the end of the drinking straw. Smooth the clay so it is rounded at the bottom (see picture at right).
Pour some water into one of the beakers.
Put your hydrometer (the straw with clay) into the beaker.
Mark the straw at the level the water comes to.
Fill the second beaker with water and add some salt.
Float your hydrometer and compare the level the water comes to (You don't need to mark it, though).
Pour cooking oil in the third beaker and float your hydrometer. Observe the level of the water on the hydrometer once again.

What's Happening?

Your hydrometer is measuring the density of the solution. When it is in the salt solution, the hydrometer doesn't sink as low because the salt makes the solution more dense than water. In the cooking oil solution, the hydrometer sinks lower than the water mark because oil is less dense than water. If something is more dense than water, it is easier to float. Whereas if something is less dense than water, it is harder to float in the solution. If you mixed the two solutions (water and oil), the oil would make a layer on top of the water. The oil is less dense than water, so it floats on the heavier solution.

Buoyancy

Explanation

The water pushes with a force equal to the weight of water displaced by the object that is added to the water. This has to do with the concept of buoyancy. About 2,200 years ago, a Greek mathematician named Archimedes made a famous discovery. He discovered that when an object is immersed in liquid, it weighs less than it weighs in air. You've probably seen this when you are in a swimming pool and can left someone that you can't lift out of the pool. Archimedes explained that this happened because the upthrust, or force, of the water pushes the object up. An object's weight pulls it down, so the upthrust of the liquid must balance this to make an object float. Thus, the weight of the liquid displaced by the floating object is the same as the force of the liquid pushing up on the object. The experiment below will show you how the upthrust of water is equal to the weight of the object.

Experiment #6: Measuring

What You'll Need:

kitchen scale
glass jar
jug
small floating object (such as a half filled jar)
rectangle baking pan
water

Directions:

Take off the weighing pan of the scales and adjust the needle of the scale so that it reads zero without anything on it.
Put the scale in the baking pan, and then put the glass jar on top of the scale.
Fill the jar with water to the brim, using the jug.
Record the weight of everything together.
Drop the object into the water. This will cause some of the water to spill out into the cake pan.
Look at the scale, and see that there is no change.
Carefully lift the jar off the scales and remove the baking plan.
Add the weighing pan again and reset the scale to zero.
Pour the water from the dish into the pan.
Write down the weight of the displaced water from the pan.
Take off the weighing pan from the scales again and adjust the needle to zero.
Weigh the floating object you used earlier.

What's Happening?

If you did the experiment carefully, you will find that the floating object is the same weight as the displaced water. The water that spills out is equal to the weight of the object that made it spill. This is the concept of buoyancy. Archimedes proved thousands of years ago that the water displaced by a floating object is the same weight as the upward force exerted by the liquid.

Tension

Explanation

Surface tension occurs when the molecules in water attract each other. In the middle of a drop, molecules pull toward each other equally in all directions. But at the surface, they are only pulled into the water because there are no molecules in the opposite direction. So the water pulls its surface tight around it like a skin. This tension is only strong enough to pull small droplets into balls, so that is why condensation and dewdrops are perfectly round. Surface tension is also responsible for making the bristles of a paintbrush cling together when it is pulled out of the water. There are many ways to break the tension. Touching the water disturbs it and breaks the surface tension, but so does adding detergent. The detergent breaks the tension where it is added to the water only, and anything on the water will be pulled to a place with greater surface tension. The experiment below demonstrates this concept.

Experiment #7: Breaking the Tension

What You'll Need:

four matches (or toothpicks)
shallow dish of water
dishwashing liquid
dropper

Directions:

Fill the dish with clean water and let it settle so the surface is completely smooth.
Carefully float the matches on the surface of the water, arranged in the shape shown at the right.
Use the dropper to add one drop of dishwashing liquid in the center of the dish.
Watch what happens to the matches.

What's Happening?

When you add the dishwashing liquid, it breaks the tension in the center of the dish. The matches are then drawn out by the stronger surface tension at the edge of the dish.