activity 40 Fast or Slow? BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN Grade K Quarter 4 Activity 40 SC.C.1.1.1 The student understands that different things move at different speeds. SC.C.1.1.2 The student knows that there is a relationship between force and motion. SC.H.1.1.1 The student knows that in order to learn, it is important to observe the same things often and compare them. ACTIVITY ASSESSMENT OPPORTUNITIES The following suggestions are intended to help identify major concepts covered in the activity that may need extra reinforcement. The goal is to provide opportunities to assess student progress without creating the need for a separate, formal assessment session (or activity) for each of the 40 hands-on activities at your grade. 1. Make three columns on the board with the following labels: Properties, Water, and Mystery Liquid. Make three rows with these labels: Color, Thick or Thin, Slow or Fast. Have students help you fill in the chart. (water: clear, thin, fast; mystery liquid: clear, thick, slow) 2. Use the Activity Sheet(s) to assess student understanding of the major concepts in the activity. In addition to the above assessment suggestions, the questions in bold and tasks that students perform throughout the activity provide opportunities to identify areas that may require additional review before proceeding further with the activity. broward county hands-on science Quarter 4 395
396 activity 40 Fast or Slow?
activity 40 Fast or Slow? OBJECTIVES In this activity, students compare the speed with which water and a liquid similar in appearance move in order to infer their thicknesses. The students compare the rate at which drops of water and drops of liquid detergent run down paper infer that some liquids are thicker than others based on how fast they drip SCHEDULE About 30 minutes MATERIALS For each student 1 Activity Sheet 40 For each team of two 2 cups, plastic, 1-oz 1 sht paper, construction, red 2 pipets 2 vials, plastic For the class 3 btls dishwashing detergent, clear 1 marker, felt-tip* paper towels* 1 roll tape, masking water, tap* *provided by the teacher PREPARATION 1 2 3 4 Make a copy of Activity Sheet 40 for each student. Use the masking tape and marker to label one of each team s vials W for water, and one M for mystery liquid (dishwashing detergent). Label each team s pipets and plastic cups in a similar fashion (see Figure 40-1). Figure 40-1. Labeling the materials. Fill each vial labeled W three-quarters full of water. Fill each vial labeled M threequarters full of dishwashing detergent. Pour the detergent into the vials slowly so that air bubbles do not get trapped within the liquid. The detergent should appear as similar to water as possible. Each student will need a copy of Activity Sheet 40. Each team of two will need a vial of water, a vial of detergent, two labeled pipets, two labeled cups, a sheet of construction paper, and several paper towels for wiping off their fingers. broward county hands-on science Quarter 4 397
BACKGROUND INFORMATION Viscosity is the measure of a liquid s resistance to flow. All liquids resist flow to some degree. However, the range of viscosity is enormous. Liquids with high relative viscosities, such as syrup, do not flow quickly; liquids with low relative viscosities, such as water or isopropyl alcohol, flow more quickly. Activity Sheet 40 Fast or Slow? Which drop ran down the paper faster? Draw a circle around it. M (The chemical used in this activity is liquid dishwashing detergent.) W The viscosity of a liquid depends on the degree of internal friction between the molecules of the liquid. As a liquid flows, its molecules move past one another. If the movement of molecules produces a high degree of friction, the liquid will move slowly. Conversely, if the movement of molecules does not produce a high degree of friction, the liquid will flow more easily. Typically, liquids made up of larger molecules have more internal friction and are more viscous. If an object is dropped through a viscous liquid, the molecules of the liquid offer a certain amount of resistance to the passage of the object through it, so the object falls slowly. The molecules of a nonviscous liquid offer less resistance, so the object falls more quickly. In this activity, students will compare the movement of water and detergent drops. From these observations, they will make inferences about the relative thickness (viscosity) of the two liquids. 398 activity 40 Fast or Slow?
1 Guiding the Activity Distribute a vial of water, a vial of detergent, two labeled plastic cups, and several paper towels to each team of two. Ask, Do the liquids in these two vials look the same? Additional Information Students will probably say they look the same. 2 Allow students to observe and touch the liquids freely for a time. Encourage them to pour the liquids back and forth between the vials and the cups and to rub a bit of each liquid between their fingers. Once students have had a chance to explore the liquids, ask, How are the two liquids the same? How are they different? Ask, Do you think the same liquid is in both vials? Explain that one of the vials contains water, but the other one contains a mystery liquid. Encourage students to share any other observations they may have made about the two liquids. Most students will note that the mystery liquid is thicker than the water. If no one mentions it, however, lead students to consider this property, even if they do not use the term thick. Ask, Did the liquids look the same as you poured them from the vials to the cups and back? How were they different? Instruct students not to mix the two liquids together. In addition, they should pour only the liquid in vial M into the cup marked M, and only the water in vial W into the cup marked W. Students can wipe their fingers off using the paper towels. Safety Note: Remind students not to put their fingers in their mouths or taste either of the liquids. Students may suggest that both liquids are clear, colorless, and wet, but that one is more slippery than the other. Based on their observations, students will probably say no, they are different liquids. Students may have noticed that when they poured the mystery liquid it ran more slowly into the cup than the water did. It also stuck to the sides much more than the water did. broward county hands-on science Quarter 4 399
3 Guiding the Activity Distribute two pipets and a sheet of construction paper to each team. Distribute a copy of Activity Sheet 40 to each student. Show students how to use the pipets to place 2 drops of each liquid at the top of the sheet of paper (see Figure 40-2). Additional Information Remind them that the pipet marked W is for making water drops and the other pipet is for use with the mystery liquid only. 4 Make sure that students place their drops at approximately the same starting height on the paper. Then have them lift the top of the paper so that the drops run down the sheet toward the bottom. Ask, Did both liquid drops move at the same speed? Have students complete their activity sheets. You may need to read the directions aloud to them. Ask students to recall other liquids they know that run slower than water. Ask students to recall other times when they have explored thick liquids. For example, have they ever dropped something small, like a raisin, into maple syrup? Into water? Ask, Did the raisin fall faster in the syrup or the water? 400 activity 40 Fast or Slow? Figure 40-2. Aligning the water and detergent drops at the top of the paper. Students should have observed that the water drops ran much more quickly than the mystery drops. Most students will be familiar with either pancake or cough syrup. Students will probably respond that the raisin fell faster in the water. They might even say that the raisin sat on top of the syrup and did not fall to the bottom at all.
5 Guiding the Activity Review with students what they have observed, that thicker liquids drip more slowly than thinner liquids. Ask, Which is thicker, the water or the mystery liquid? How do you know? Additional Information The mystery liquid is thicker because drops of the mystery liquid ran more slowly than the drops of water. Reveal to students that the mystery liquid is dishwashing soap. In conclusion, ask, What is one way that the water and the dish soap are different? Lead students to conclude that not all liquids are the same thickness. R EINFORCEMENT Have students place drops of both liquids on different surfaces and compare how fast they run. They should find that although the drops run at different speeds on different surfaces, the water always runs faster than the detergent. SCIENCE JOURNALS Students should respond that the soap is thicker than the water. Have students place their completed activity sheets in their science journals. C LEANUP Remove the masking tape labels from the cups, vials, and pipets. Have students rinse their vials, cups, and pipets with water and leave them to air dry before returning them to the kit. Discard the used construction paper. SCIENCE AT HOME Have students perform the test at home using safe household liquids such as milk, cream, juice, ketchup, white glue, and so on. Make sure students understand that they should ask their parents permission to do this activity and their parents should be with them when they do it. broward county hands-on science Quarter 4 401
Connections Science Extension Provide several other liquids for example, white glue, vinegar, clear juice, a saturated sugar solution, and soda water in numbered cups, and let each team use its own method to compare each liquid s thickness to the thickness of water. (Safety Note: Remind students not to taste any of the liquids.) You may want to have each team record its results on a simple three-column chart with the headings Less Thick than Water, Same as Water, and More Thick than Water and the cup numbers noted in the appropriate columns, or you could draw the chart on the board and record the results yourself as teams work. (Also see Science and Math below.) Science and Math As a follow-up to the Science Extension above, you could have older or more capable students work out the relative thicknesses of water and the other liquids they used in the basic activity and the Science Extension above. When each team has determined the relative thicknesses, ask them to sequence the cup numbers from left to right on a line from least thick to most thick. Let the teams compare their sequences to see whether they are the same. (Depending on the liquids used, there may be minor differences in the teams sequences, but there should be no major differences.) Science and Social Studies Research and share with students the early development of detergents as soap substitutes. (Animal fat is needed to make soap. The first synthetic detergents were produced by the Germans during World War I so that available animal fats could be used for other purposes.) 402 activity 40 Fast or Slow? Science, Technology, and Society Give each team a small jar with a tight-fitting lid. Have students fill the jar about one third full of water and then add an equal amount of cooking oil. Tell them to screw the lid on tightly and shake the jar well to mix the water and oil. When students put the jar back down, the oil and water will separate into two layers. Now have students remove the lid, add a few drops of liquid detergent, replace the lid, and shake again. This time, the oil and water will not separate but will produce a cloudy mixture. Tell students that the detergent breaks the oil into tiny drops that hang in the water and make it look cloudy. Explain that dishwashing soap and laundry detergent work in this same way to remove grease from dishes and oily dirt from clothes, mix it with water, and wash it away.