Monday, September 13, 2010
What is Density?
Take a look at the two boxes above. Each box has the same volume. If each ball has the same mass, which box would weigh more? Why?
The box that has more balls has more mass per unit of volume. This property of matter is called density. The density of a material helps to distinguish it from other materials. Since mass is usually expressed in grams and volume in cubic centimeters, density is expressed in grams/cubic centimeter
That sinking feeling? Water Temperature and Density
Why does the water always seem colder at the bottom of a lake? Is it because the sun only shines on the top or is there another reason? Why are icebergs so dangerous for ships at sea and what's unique about the way water changes from liquid to solid? If these questions have puzzled you in the past, or if you're bored with winter and just want to do some "cool" experiments, I've got a challenge for you!
Here's what you'll need to play along:
* 3 tall (12 oz.) clear glasses half full of room temperature water
* A glass of ice water
* A glass of hot tap water
* A plastic soda bottle -- with cap -- filled with water
* A freezer
* Red and blue food coloring
* Some ice cubes
Drop a few ice cubes into a glass of room temperature water. What do the ice cubes do? If you said they float, congratulations. You've just proven that ice is less dense than liquid water! Ice is "cool" stuff because most substances actually get denser when they change from a liquid to a solid, but not water.
As water freezes into ice, the volume actually increases. To check this out, take an empty plastic soda bottle and fill it completely with water. Seal it up tight with the cap and stick it in the freezer for a few hours.
Okay, so if water gets less dense when it freezes, then what happens when different-temperature waters meet?
Here's the challenge:
How do different-temperature waters react when they flow together? Do they sink, float, or mix together?
What you do:
Begin by predicting what will happen when ice-cold water meets room-temperature water. Then predict what will happen when hot tap water meets room temperature water. Make sure you explain why you think this might happen. After you've made your predictions, put a few drops of blue food coloring into the ice-cold water and slowly pour it into one glass of room temperature water. What does it do? Was your prediction right? Now mix a few drops of red food coloring into the hot tap water and slowly pour it into another glass of room temperature water. Did it do the same as the cold? Based on your experiments, what do you think happens to the density of water as it changes temperature?
Here's what you'll need to play along:
* 3 tall (12 oz.) clear glasses half full of room temperature water
* A glass of ice water
* A glass of hot tap water
* A plastic soda bottle -- with cap -- filled with water
* A freezer
* Red and blue food coloring
* Some ice cubes
Drop a few ice cubes into a glass of room temperature water. What do the ice cubes do? If you said they float, congratulations. You've just proven that ice is less dense than liquid water! Ice is "cool" stuff because most substances actually get denser when they change from a liquid to a solid, but not water.
As water freezes into ice, the volume actually increases. To check this out, take an empty plastic soda bottle and fill it completely with water. Seal it up tight with the cap and stick it in the freezer for a few hours.
Okay, so if water gets less dense when it freezes, then what happens when different-temperature waters meet?
Here's the challenge:
How do different-temperature waters react when they flow together? Do they sink, float, or mix together?
What you do:
Begin by predicting what will happen when ice-cold water meets room-temperature water. Then predict what will happen when hot tap water meets room temperature water. Make sure you explain why you think this might happen. After you've made your predictions, put a few drops of blue food coloring into the ice-cold water and slowly pour it into one glass of room temperature water. What does it do? Was your prediction right? Now mix a few drops of red food coloring into the hot tap water and slowly pour it into another glass of room temperature water. Did it do the same as the cold? Based on your experiments, what do you think happens to the density of water as it changes temperature?
What is matter?
Matter, matter everywhere.
There's matter in your hair.
Matter in the air.
There's even matter in a pear!
There's liquid matter, solid matter, and matter that's a gas.
Even you are matter, because you have volume and mass!
Okay, so maybe I'm not a poet, but that's how I describe the "stuff" we call matter. In trying to make sense of the universe, scientists have classified everything that exists into two broad categories: matter and energy. Simply stated, matter can be thought of as "stuff" and energy is "the stuff that moves stuff."
Matter PixNow, if you take all the "stuff" in the world, you know that there are many different types. To further simplify things, matter has been broken down into three basic types, or "states of matter": solids, liquids, and gas. (Actually there are more than three, but we're going to concentrate on the main forms here.)
Matter can change from one state to another, which we call a "physical change." Physical changes usually occur when heat (energy) is either added or taken away. A good example of a physical change is when an ice cube melts. It starts as a solid but when you add heat, it turns into a liquid. The cool thing about a physical change is that it can be reversed. If you take the liquid water from the melted ice and cool it down again (remove the heat), it turns back into a solid!
There's matter in your hair.
Matter in the air.
There's even matter in a pear!
There's liquid matter, solid matter, and matter that's a gas.
Even you are matter, because you have volume and mass!
Okay, so maybe I'm not a poet, but that's how I describe the "stuff" we call matter. In trying to make sense of the universe, scientists have classified everything that exists into two broad categories: matter and energy. Simply stated, matter can be thought of as "stuff" and energy is "the stuff that moves stuff."
Matter PixNow, if you take all the "stuff" in the world, you know that there are many different types. To further simplify things, matter has been broken down into three basic types, or "states of matter": solids, liquids, and gas. (Actually there are more than three, but we're going to concentrate on the main forms here.)
Matter can change from one state to another, which we call a "physical change." Physical changes usually occur when heat (energy) is either added or taken away. A good example of a physical change is when an ice cube melts. It starts as a solid but when you add heat, it turns into a liquid. The cool thing about a physical change is that it can be reversed. If you take the liquid water from the melted ice and cool it down again (remove the heat), it turns back into a solid!
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