Hobbies And Interests
Making Saltwater
Creating saltwater as your students watch gives you a chance to introduce the idea of dissolving a material. Begin by teaching students that one of the differences between the water in the ocean and the water we drink is that ocean water is very salty. Heat a clear beaker of water, making sure that the children do not touch any hot surfaces. Begin to pour in salt and stir it to dissolve the salt into the water, and discuss with your students why the salt disappears as you stir.
Heavy Water
You can use analogies to help make sense of the idea of water density for first graders. For example, you might explain that water with salt dissolved in it is heavier than water without salt in it, rather like a backpack with books in it is heavier than a backpack with crumpled newspaper in it, even though both backpacks are the same size. Teach that the more salt the water holds, the denser it will be.
Temperature Activity
Another major factor in the density of ocean water is its temperature. Cold water is denser than hot water. To illustrate the principles behind this fact, ask your students to stand or sit as close together as they can. Then permit them to begin moving around. Point out that when they started moving they took up more space, even though the number of children never changed. In the same way, as water molecules' internal energy rises, causing the molecules to move, the water grows less dense.
Layers of Water
The varying density of ocean water leads to the natural formation of layers. You can create a visual demonstration of this effect. Prepare saltwater ahead of time by heating water to the boiling point and adding salt until it stops dissolving. Chill the salt water and add a few drops of blue food coloring to tint it. Tint some fresh water with red food coloring. When it is time for the demonstration, warm the red water. Pour a trickle of red water down the inner edge of a container of blue to form two layers.