WaterWater Investigation 1 Part 2: Surface Tension

Essential Question What factors influence the shape of water?

What You Will Learn The shape of water on a flat surface. Water has a property that affects its shape. This property of water can be affected by the addition of other substances.

Question How many drops of water do you think you can fit on a penny? Raise your hand and we’ll record your guesses.

Task You will work in pairs to place drops of water on a penny following the procedure I’m demonstrating. a.Place a dry penny on a paper towel. b.Use a dropper to placed drops on the penny one at a time. c.Hold the dropper straight up and down and release drops from about 1 cm above the penny. d.Count the number of drops as you go until the water spills.

Directions The getters will get a tray with enough materials for each pair of students when I say “materials.” Working in pairs take turns dropping drops on the pennies. Record the number of drops on the penny each time before the water falls off the penny. Dry off the pennies between each trial.

Discuss the Results What was the most drops you could drop on the penny before the water ran off? Record these amounts next to the estimates. What shape was the surface of the water on the penny before it spilled?

Discuss Results This is a side view of the penny and the water.

Vocabulary Surface Tension – the skinlike surface on water (and other liquids) that pulls it together into the smallest possible area (sphere) Dome – the shape a drop of water takes when it is on a flat surface. It is like a flattened hemisphere.

Surface Tension The curved surface of the water shows us an interesting property of water. Scientists call this property surface tension. Surface Tension causes water to stick together and try to form into a ball.

Question What will happen if soapy water is added to a water dome on a penny? Discuss this with your partner. Share.

Task a.Set up as before with a dry penny on a paper towel. b.Put 15 drops of plain water on a penny to make a dome. c.While observing the dome from the side, add one drop of soapy water to the dome. d.Count the number of additional drops of soapy water needed to spill the dome.

Directions When I say “materials,” the getters will get a cup of soapy water, a new dropper, and a clean dry penny. Make sure that the new dropper is used only in the soapy water. Do not put this dropper in the plain water. Do not put the dropper you use in the plain water in the soapy water.

Directions Cont’d Materials. You may begin. Be sure to record the number of drops.

Discuss Results Reporters, what happened to the water dome on the penny when soapy water was added? Does soap affect surface tension? How do you know? Discuss in your groups. Share.

Directions We will do the same task as before, but this time we will use salt water. When I say “materials,” the getters will get a cup of salt water, a new dropper, and a clean dry penny. Make sure that the new dropper is used only in the salt water. Do not put this dropper in the plain water.

Discuss Results Reporters, what happened to the water dome on the penny when salt water was added? Does salt affect surface tension? How do you know? Discuss in your groups. Share.

CONTENT/INQUIRY What shape does water make on a flat surface? Water forms a dome on a flat surface. Why does water form a dome on a flat surface? Surface tension makes water form a sphere or dome. How did you change the surface tension of plain water? Soap added to water reduces its surface tension. The dome flattens when soap is added to water.

Clean Up All students must neatly put their materials on the tray. The collectors will take the materials back to the science table.

Vocabulary Review Surface Tension – the like surface on water (and other liquids) that pulls it together into the smallest possible area (sphere) Dome – the shape a drop of water takes when it is on a flat surface. It is like a flattened hemisphere.

What You Learned Today Water forms a dome on a flat surface. Surface tension makes water form a sphere or dome. Soap added to water reduces its surface tension. The dome flattens when soap is added to water.

Record Observations Record your observations during these tasks on the Surface Tension Record sheet.