Category: Physics

Water Properties Notes

 

Water Properties
States of Water
Adhesion and Cohesion
Surface Tension
Capillary Action

The States of Water

Water has three states. Below freezing water is a solid (ice or snowflakes), between freezing and boiling water is a liquid, and above its boiling point water is a gas. There are words scientists use to describe water changing from one state to another. Water changing from solid to liquid is said to be melting. When it changes from liquid to gas it is evaporating. Water changing from gas to liquid is called condensation (An example is the ‘dew’ that forms on the outside of a glass of cold soda). Frost formation is when water changes from gas directly to solid form. When water changes directly from solid to gas the process is called sublimation.

Gas
Liquid
Solid

Most liquids contract (get smaller) when they get colder. Water is different. Water contracts until it reaches 4 C then it expands until it is solid. Solid water is less dense that liquid water because of this. If water worked like other liquids, then there would be no such thing as an ice berg, the ice in your soft drink would sink to the bottom of the glass, and ponds would freeze from the bottom up!

Water is found on Earth in all three forms. This is because Earth is a very special planet with just the right range of temperatures and air pressures.

Adhesion and Cohesion

Water is attracted to other water. This is called cohesion. Water can also be attracted to other materials. This is called adhesion.

The oxygen end of water has a negative charge and the hydrogen end has a positive charge. The hydrogens of one water molecule are attracted to the oxygen from other water molecules. This attractive force is what gives water its cohesive and adhesive properties.

Surface Tension

Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water. Try this at home: place a drop of water onto a piece of wax paper. Look closely at the drop. What shape is it? Why do you think it is this shape?

What is happening? Water is not attracted to wax paper (there is no adhesion between the drop and the wax paper). Each molecule in the water drop is attracted to the other water molecules in the drop. This causes the water to pull itself into a shape with the smallest amount of surface area, a bead (sphere). All the water molecules on the surface of the bead are ‘holding’ each other together or creating surface tension.

Surface tension allows water striders to ‘skate’ across the top of a pond. You can experiment with surface tension. Try floating a pin or a paperclip on the top if a glass of water. A metal pin or paper clip is heavier than water, but because of the surface tension the water is able to hold up the metal.

Surface tension is not the force that keeps boats floating.

Capillary Action

Surface tension is related to the cohesive properties of water. Capillary action however, is related to the adhesive properties of water. You can see capillary action ‘in action’ by placing a straw into a glass of water. The water ‘climbs’ up the straw. What is happening is that the water molecules are attracted to the straw molecules. When one water molecule moves closer to a the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw. Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher up capillary action will pull the water (Can you make up an experiment to test this?).

Plants take advantage of capillary action to pull water from the into themselves. From the roots water is drawn through the plant by another force, transpiration.

Why Boats Float

How does a heavy boat float?

 

A boat, or any other object designed to float, is based on a theory by a very old guy, even older than Capt. Matt. Though he is old and, by the way, dead, he was really a cool guy and his name was Archimedes (Ark-i’-meed-eez). His principle, cleverly named the Archimedes’ Principle, explains how things float.

If you fill your bathtub with water, what happens when you get in? The water rises, right? (And sometimes goes over the side.) That is because you “displaced” some of the water with your body and it had to go somewhere. The key to floating is that the object must displace an amount of water which is equal to its own weight.

For example, suppose you had a block of wood that was 1 foot square. Let’s say that this block of wood weighs about 50 pounds. Now say we lower that wood into the water. The wood will move down into the water until it has displaced 50 pounds of water. That means that fifty pounds of water are pushing back up on the block and making it float.

The principle of floating is pretty easy, however, if you want to remain inside the boat and actually get where you want to go, your boat must have “stability” as well as being able to float. Stability means that it is designed not to tip over easily. That doesn’t mean it won’t ever tip over.

 

stability1.jpg (8249 bytes)

 

On a large ship like an ocean liner or tanker, the movement of one person doesn’t affect the stability of the ship because it was designed to safely carry lots of weight. But on a small boat, like a fishing boat, your weight and the weight of your gear (and where you put it) has an effect on the stability of the boat.

 

stability2.jpg (11938 bytes)

 

A boat is said to “heel” (no not the one on your foot) when it leans over to one side. This is why you never want to sit or step onto the side of a boat. Your weight could make it “heel” too much and it may tip over. You should also balance the weight of all the stuff you bring with you. In a small boat, you and your gear should always stay low and to the center of the boat. When getting into a small boat, always try to step into the center and keep “one hand for yourself and one for the boat.”

 

stability3.jpg (11482 bytes)

 

Of course, because you have on your PFD and are displacing enough water to float, you would be okay, just a little wet and cold. If this should ever happen to you and you can’t right the boat (turn it back over), stay with the boat, blow your whistle or yell for help.

So . . . the next time someone says “Whatever floats your boat” tell them about Archimedes and stability and why it’s a very good idea to always wear your life jacket!

 

Electricity Elementary

 

   ELECTRICITY

 

Standards:

  • PS.7.4.2   Classify electrical conductors and electrical insulators
  • PS.7.4.3   Construct simple circuits from circuit diagrams

Notes:

  • What is Electricity? – Just the basics about electricity
  • Circuits Can Be Electrifying! – All types of circuits covered — open, closed, series, and parallel
  • Static Electricity and Dryer Sheets! – Covers that problem of static cling in your clothes
  • Electricity and Magnetism –  Tells students how these two are related
  • Conductors and Insulators – What will and what won’t conduct an electric current and why

Interactive Activities:

Smart Board Activities:

Labs:

  • Complete the Circuit Game! — Elementary students will love this activity by competing with each other for the most steady hand!  They’ll learn something about open and closed circuits too!!

 

Great Links:

 

 

BI Sample 2 Lab Volume of Object

 

 

Volume of an Irregular Object

 

 

Introduction

 

Everything is made of matter. Matter has physical and chemical properties. Physical properties are observable, such as mass, volume, and density. Mass is a fundamental property of an object generally regarded as equivalent to the amount of matter in the object. Volume is the amount of space it takes up. Density is the thickness of it the formula for density is D=M/V. The purpose of this experiment was to find the mass, volume, and density of three different objects.

 

Hypothesis

 

Determining the volume of an irregularly shaped object can help in determining density.

 

Materials

 

The materials used included a rubber stopper, a rock, a shell, a 100mL graduated cylinder, water, electronic balance, paper, and pencil.

 

Methods:

 

Obtain rubber a stopper, a shell, and a rock. Estimate and record the mass and volume of the three objects. Weigh and record each object. Take the graduated cylinder and fill halfway with water and record the volume. Add one object and record the new volume. Subtract initial volume from final, and record. Repeat with the other three objects.

 

Results:

 

ObjectEstimated mass (g)Estimated volume (ml)Actual mass (g)Volume of H2O (ml)Volume of object + H2O (ml)Object’s Volume (ml)Density D=m/v

(g/ml)

Rubber Stopper8g65ml8.3g50ml56ml6ml1.38g/ml
Shell2g55ml3.1g50ml53ml3ml1g/ml
Rock4g60ml7.8g50ml54ml4ml1.95g/ml

1. How did you determine the object’s:

a. Mass? Weighed it on a electronic balance

 

b. Volume? Put it in the water and measured the volume then subtracted the volume of the water before the object.

c. Density? Divided mass into volume

2. How did your estimates of mass and volume compare to the actual mass and volume of each object?

Our estimates of mass were close to the actual mass. Our estimates of volume were off not close to the actual volume at all.

3. Objects will sink if they are denser than water. Explain why ships made of steel float instead of sinking since steel is denser than water.

Because the ship has a hallow cavity with trapped air in it.

 

Error Analysis:

 

The volume of the water might not have been measured correctly.

 

Discussion and Conclusion:

 

The volume of the rubber stopper, rock and shell were determined by submerging them in a graduating cylinder containing water. The original water level in the cylinder was subtracted from the final water level to get the volume (ml) of each object. The actual mass (g) of each object was obtained by placing each on an electronic balance. Density could then be determined by dividing the mass of each object by its volume. The data showed the rock to have the greatest density at 1.95 g/ml with the rubber stopper 1.38 g/ml and the shell 1 g/ml being less dense.