Lab / experiment Grade 6 Health & Consumer Science
The Cold-Water Wait: Timing the Tap at Copperbeck Middle
A grade 6 health lab in which students time how long a tap runs before it turns cold, catch and measure that water, and find the flow rate per second.
Objectives
- Students will time how long a tap runs before the water feels cold and record the volume caught.
- Students will calculate a flow rate in milliliters per second from their own timed measurement.
- Students will summarize the class wait times using the median and the range.
Vocabulary
- Flow rate
- Flow rate measures how much water moves past a point in a certain amount of time, like gallons per minute through a garden hose. Bigger pipes and stronger pushes give bigger flow rates.
Also: unit rate, median, range
Teacher overview
Most people run the tap for a while before the water turns cold enough to drink, and that water goes down the drain unmeasured. In this lab students catch it, measure it, and turn the measurement into a flow rate per second, which is the same kind of unit rate a plumber or a utility uses. One claim worth testing rather than settling by argument is that opening the faucet wider brings the cold water sooner and so wastes less water. Opening it wider does shorten the wait in seconds, yet the pipe still holds the same warm water that has to be pushed out, so the volume caught in the bucket stays close to the same. Step 7 puts the claim to a measurement.
Procedure
Step 1 (safety, before you start): Use the cold tap only. Do not drink or taste any water in this lab. Keep the bucket on the floor of the sink or on a flat counter so it cannot tip, and wipe up spills right away so nobody slips.
Step 2 (set up your station): One person holds the bucket under the tap. One person works the timer. One person records. Trade jobs after each trial so everyone measures at least once.
Step 3 (agree on what "cold" means): Before any water runs, decide as a group how you will judge cold. The simplest test is to hold a clean finger in the falling stream above the bucket, not in the water already caught, and call it cold when it stops feeling warm. Write your rule on the data sheet so every trial uses the same rule.
Step 4 (run trial 1): Start the timer at the same moment you open the cold tap about halfway. Catch all the water in the bucket. Stop the timer the second the water feels cold, and close the tap. Record the time in seconds.
Step 5 (measure what you caught): Pour the water from the bucket into the measuring cup a little at a time and add up the milliliters. Record the total volume. Pour it out and dry the bucket.
Step 6 (run trial 2 the same way): Repeat Steps 4 and 5 with the tap opened halfway again. Record the second time and the second volume in the table.
Step 7 (test the wide-open claim): Run one more trial with the tap opened all the way. Record the time and the volume in the last row of the table. This trial is the one that tests whether opening the tap wider changes the volume, the wait, or both.
Step 8 (share with the class): Write your three wait times on the class chart at the board so the whole group has one pooled set of numbers to describe.
Data & Analysis
| Trial | Tap opening | Wait until cold (seconds) | Volume caught (mL) |
|---|---|---|---|
| 1 | Halfway | ||
| 2 | Halfway | ||
| 3 | Wide open |
- Find the mean of your two halfway trials for wait time in seconds, and the mean of the two volumes in milliliters.
- One group at another sink timed 22 seconds and caught 1,100 mL in that time. What was that tap's flow rate in milliliters per second?
- Use your own trial 1 numbers to find your flow rate in milliliters per second. Divide the volume you caught by the seconds you timed.
- Compare your wide-open trial with your halfway trials. Did the wait time change, did the volume change, or did both change? Use your own numbers to answer.
- Suppose a household waits for cold water 6 times a day and loses 900 mL each time. How many milliliters go down the drain in one day?
- Look at the class chart of wait times. Report the median and the range, and explain what those two numbers together tell you about the sinks in this building.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Answer: Accept any pair of means that matches the group's own two halfway trials. Add the two wait times and divide by 2, then add the two volumes and divide by 2. Check the arithmetic against the numbers written in the table rather than against a fixed value.
- Answer: 50 mL per second. Divide 1,100 mL by 22 seconds, which gives 50 milliliters each second. Students who write the answer as a rate with the word "per" have used unit-rate language correctly.
- Answer: Accept any rate the group's own trial 1 supports, found by dividing the recorded volume by the recorded seconds. Most classroom taps opened halfway land somewhere between 20 and 90 milliliters per second, so a rate far outside that range usually means a measuring error worth rechecking.
- Answer: The wait time normally drops while the volume stays close to the same. Accept any answer supported by the group's own three rows. The reasoning that earns full credit says the pipe holds the same warm water either way, so a faster stream clears it in fewer seconds without saving much water.
- Answer: 5,400 mL. Six waits at 900 mL each gives 6 times 900, which is 5,400 milliliters in one day.
- Answer: Accept the correct median and range read from the class chart. The median is the middle wait time once the class list is in order, and the range is the largest wait minus the smallest. Together they show the typical wait and how much the sinks differ from each other.
Differentiation
Support
Give these students a data sheet with the division already set up as a fraction bar, volume on top and seconds on the bottom, and let them use a calculator. Pair them with a partner who runs the timer so they can focus on reading the measuring cup at eye level.
Extension
Ask students to design a fair way to compare two sinks in different parts of the building, then explain in writing which parts of their method keep the comparison fair and which parts they could not control.
ELL supports
Pre-teach "tap," "flow rate," "median," and "range" with a labeled picture of a sink, a bucket, and a number line. Provide the sentence frame: "Our tap ran for ___ seconds and filled ___ milliliters, so the flow rate was ___ milliliters per second."
Extensions
Have students repeat one trial at a sink that has not been used all morning and compare it with the same sink after it has been used all day, then write two sentences about why the wait might differ.