Milk should be poured into the observation tray so that it is room temperature. For secondary grade level the student can pour the milk into the observation tray. Student will take temperature of milk with thermometer allowing milk to adapt to room temperature. Have students state their hypothesis while measuring temperature of milk.
· Whole milk *Note: various types of milk can be given to see what effects their composition will have on the outcome of the experiment - $1.79 for ½ gallon
· Tin pie plates (observation tray) - $1.00 at dollar store
· 4 different colors of food coloring - $3.29 for a pack of four at Publix
· Dish – washing soap [Dawn works better] - $1.00 at dollar store
· Tooth picks - $1.00 at dollar store
1. Pour enough milk in the observation tray to cover the bottom. Allow it to settle.
2. Add one drop of each color of food coloring in the center of the tray. Be sure to keep the drops close together.
3. Use a toothpick. Have student to document their problem and hypothesis in their scientific notebook. What is in milk and food coloring? What will happened once student touch the center of the milk while being careful not to stir. Observe what happens.
4. Next place tooth pick in any brand of dishwashing liquid. Ask students to predict what will happen if they place the soapy toothpick into the center of the milk. Place the soapy end into the milk and hold it there for 10-15 seconds. Watch and observe the burst of color!
Ask the students to explain why this happened when soap was placed in the milk. Have students to test their experiment by placing the soapy toothpick at different areas of the milk in that is the observation tray. Notice that the colors continue to move even after the toothpick has been removed.
5. Students my repeat experiment using water in the place of milk to make a comparison. Will you get the same eruption? Why? Or why not? What kind of milk produces the best swirls: skim, 1%, 2%, whole milk, and chocolate milk? Why? Or why not? (Teacher will place student in groups to perform experiments using different types of milk and explain observation and what happened.
Student will learn that water molecules break up when soap is added to its content.
Student will document their trials observations into their science journal notebook.
Water molecules have strong cohesive bonds - the tendency of “like” molecules to stick together (water to water). It also has strong adhesion bonds – the tendency of “unlike” molecules to cling together such as water and the molecules of silicon dioxide on the walls of a drinking glass. The tensile strength is related to cohesion and is a measure of the resistance of molecules to being pulled apart. This phenomenon is responsible for “surface tension”.
Since milk is a liquid it has surface tension like water. The drops of food coloring float on the surface. Liquid soap wrecks the surface tension by breaking the cohesive bonds between water molecules allowing the colors to zing throughout the milk.