# Density – Buoyancy

Density – Buoyancy

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Every object on earth is made of atoms. Gravity pulls these atoms to the earth. You can measure the pull of gravity on an object – we call that measurement weight.

Density  is how close together the molecules of a substance are or how much mass a substance has in a given space. If you have one cup of jelly beans and one cup of marshmallows…the jelly beans have more mass…there is more “stuff” compacted into the cup. The marshmallows are mostly air. If you put each of those cups in a microwave to melt…the sugar and water that makes up the jelly beans would almost fill the cup to the top. The sugar and water that makes up the marshmallows would only fill the cup a little bit because marshmallows have less mass, they are mostly made of air. Materials with more density weigh more. A cup of jelly beans weighs more than a cup of marshmallows.

For an object to be bouyant, or float, it must have less density that what it is floating in, or it has to have something attached to it that helps it float – like you with a life jacket on.

You Will Need:

• Drinking Glass
• Clear Soda
• Water
• Ten Raisins

Fill one clear glass up with water and drop in five raisins. Fill another clear glass up with clear soda like sprite or 7up. Drop in five raisins. What happens when you drop the raisins in? What a few minutes – now what is happening to the raisins in each glass? Can you guess why the raisins are behaving differently?

Raisins are heavier than the water in the drinking glass. The raisins are also heavier than the soda in the drinking glass. At first, both sets of raisins sink to the bottom of the glass, they don’t float.

But the soda has little air bubbles in it – the carbioation. These bubbles are attracted to the rough surface of the raisins and stick there. When there are enough of these little carbonated balloons (the bubbles) stuck to the raisins the bubbles lift the raisins to the surface making the raisin float. The bubbles are like little temporary life jackets. When the bubbles pop and the gas inside them escapes into the air…the raisins don’t have anything to help them float anymore and they sink to the bottom of the glass again.

Science Experiment Idea: Try putting other small objects in soda to see if the bubbles will attach to them and help them float to the surface of the soda. Try a penny, a toothpick, a peanut, a skittle. Can you find something that the bubbles will float to the surface like the raisin?

# Websites:

More IndyPL Experiments about Density

# DVDs:

Download this Hoopla DVD to your device with your IndyPL library card – no waiting! Hoopla Directions

 Bill Nye the Science Guy Season 1 Episode 5: Buoyancy – Bill Nye takes to the sky in a hot air balloon and goes scuba diving in the Seattle Aquarium to explain why objects like boats, helium, and balloons are buoyant.

Words to Know:

Density – How closely packed together the molecules of a substance are.
Bouyancy – Ability to float or rise to the top of a liquid or gas.
Float – To sit near the surface of a liquid or gas, to not sink.
Mass – How much matter fits in a given space.
Matter – Stuff
Weight – A measure of the force of gravity on an object. Materials with more density weigh more.
Volume – How much space a substance takes up.
*****The confusing relationship between weight and mass: On earth, a bowling ball can weigh about 10 pounds. If you take that same bowling ball to the moon it will weigh much less because the graviational pull of the moon is less than the gravitational pull on the earth. Weight is a measure of gravitational pull. So the weight of the bowling ball, or anything else, changes depending on where you weigh it. The mass of the bowling bowl does not change no matter where it is. The bowling ball has the same amount of mass  on earth as it does on the moon or anywhere else you take it.

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# Science Experiments

Science Experiments

Looking for an idea for a science project? Here are several science experiment ideas that use materials easily found in your house. A couple of them might require a trip to the grocery store or pharmacy, but mostly you can just raid the garage, kitchen or medicine chest for the ingredients. Many experiments you will want to do OUTSIDE. Each experiment will give you directions as well as suggest websites and books that will help you explain what science is at work during the experiment. Science Experiments

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# Miscible Molecules: Lava Bottle

Miscible Molecules: Lava Bottle

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Sometimes when atoms come together to form a molecule, one end of the molecule has a positive charge and one end of the molecule has a negative charge. When this happens the molecule is a polar molecule. Molecules that do not have two electrical poles are called non-polar molecules.

This experiment will  show you how polar molecules and non-polar molecules behave when added together. If two kinds of molecules are added together that are both polar molecules, they will mix. They are miscible. Miscible means that the two things can mix together. If two non-polar molecules are added together they will also mix and are miscible. However, if a non-polar molecule and a polar molecule are added together, they will not mix together. This is called imiscible. Imiscible means that the two kinds of molecules CANNOT mix together.

What You Need:

• Plastic Bottle
• Water
• Vegetable Oil
• Food coloring
• Measuring Cups
• Alka Seltzer

Fill the bottle about 3/4 of the way up with vegetable oil. Fill the bottle the rest of the way up with water. Now add some drops of food coloring. Close the cap on the bottle and shake it up. What happens?

Break the alka seltzer tablet in half. Open the bottle and drop in one half. What happens? Once the bubbles settle down drop in the other half. What happens again?

Water is a polar molecule. Vegetable oil is a non-polar molecule. These two substances do not mix together, they are imiscible (they will not mix together). That’s why you see the blobs of water bobbing around in the oil. Food coloring is a polar molecule so it WILL mix with the water. The water and the food coloring are both polar molecules will mix together. That’s why the water blobs turn the color of the food coloring and the oil does not.

The alka seltzer just makes the bottle more fun because it makes the colorful water blobs move without shaking the bottle. The alka seltzer tablets dissolve in the the water and make carbon dioxide gas (like we saw vinegar and baking soda do in the Exploding Ziploc experiment). The carbon dioxide gas bubbles attach to the colorful water blobs and make them float to the top of the bottle. When the gas bubbles pop there is no gas bubble to hold up the water blob, so it slowly floats back down to the bottom of the bottle.

Here are some website and books that will give you good directions for making your own lava bottle and understanding molecules and polarity:

Science Experiment Idea: Make several different lava lamps using different liquids for the water. Try vegetable oil and water, like our experiment today. Then try vegetable oil and rubbing alcohol or vegetable oil and orange juice or vegetable oil and olive oil. See if you can determine which substances are miscible when added together. Which ones make a good lava lamp and which ones don’t?

Words to Know:

Polarity – When atoms align.
Atoms – The smallest, most basic unit of matter. An atom is made up of a nucleus surrounded by electrons.
Molecules At least two atoms held together by a chemical bond.
Polar Molecule A molecule that has two opposite electrical poles. One end of the molecule has a positive charge and one end of the molecule has a negative charge.
Non-Polar Molecule – A molecule that does not have opposite electrical poles.
Miscible – Able to mix when added together.
Imiscible – Not able to mix when added together.

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# Transpiration – Flower Transformation

Transpiration – Flower Transformation

Find More Science Experiments Plant parts like petals, leaves and stems have little holes called stomata – kind of like the pores in our skin. When stomata open, water escapes. When this happens the water is replaced by the plant absorbing water up from the roots into the stem and leaves and petals. As water evaporates from the leaves and petals more water is sucked up through the stem from the roots. This is called tranpiration…kind of like a person sucking on a straw. What You Need:

• White Flowers (Carnation, Queen Anne’s Lace)
• Food Coloring
• Water
• Vase

Fill a vase with water. Add food coloring to the water. Collect or buy some white flowers. Make a fresh cut at the end of the flower stem and put the flowers in the water. Check on the flowers every hour. How are the petals changing?

Words to Know: Cohesion – When molecules of the same substance stick together. Transpiration – The loss of water from the parts of plants; petals, leaves, stems, flowers, etc. Absorb –  To soak up. Evaporation – Water changing from a liquid to a vapor.

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# Air Pressure – Do Not Open Bottle

Air Pressure – Do Not Open Bottle

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Even though air seems like nothing, it really is something. Gases like air, even though they are not visible to our eyes, are made up of molecules just like solid objects. These molecules are pulled toward the earth by gravity.

Earth is surrounded by a layer of air that is heavy. That layer of air exerts pressure on the surface of the earth, a lot of pressure. Our bodies are used to it so it doesn’t bother us. In fact, we are so used to it that what bothers us is when the air pressure is gone.

The higher you go in the atmosphere, the less air pressure there is because the “thickness” of the air is less the higher you go. That’s why airplanes have “pressurized” cabins. We can’t survive in too little air pressure.

What You Need:

• Empty Water Bottle
• Thumb Tack
• Water

As the bottle is filled with water the water pushes any air left in the bottle out. When you put the lid on no air can get in the botter either. Air on the outside of the bottle is pushing on it as well as the lid. The small holes in the bootle aren’t big enough for air to sneak in and increase the air pressure on the water…but when you open the cap more air can get in and press down on the water making it leak out the holes.

Here are some websites and books that will help you understand air pressure:

Words to Know:

Air Pressure – The force that air exerts due to it’s weight. Even though air seems like nothing, it really is something. Gases like air, even though they are not visible to our eyes, are made up of molecules just like solid objects.

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