Water Clock: Does the Amount of Water in a Water Clock Affect its Accuracy?
Unlike sundials, water clocks do not depend on the daylight hours or a sunny day. This fact made water clocks useful timekeeping devices among ancient cultures. There are many different versions of water clocks. Ancient water clocks used one container with markings on it. A later design has water drip at a constant rate from one container into another container below it. The height of the water in the bottom container indicates the amount of time that has passed since the clock was started.
One challenge in designing an accurate water clock relates to the rate at which the water flows or drips out of the container. The quantity of water in a container is one factor that can affect the drip rate of the water. In a container of water, all the water pushes downwards, causing pressure on the water at the bottom. A greater quantity of water will cause a greater quantity of pressure pushing downwards; less water will result in less pressure.
In this experiment you will investigate how the amount of water can affect a water clock's accuracy. You will first make a simple water clock and measure a specific period of time with the water always remaining at a constant level. This will be your control.
You will then use three different levels of water that will each drip into the container: a quarter, half, and three-quarters filled.
Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of water clocks and timekeeping. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
- the topic of the experiment
- the variable you will change
- the variable you will measure
- what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through further investigation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: "As the amount of water in a water clock decreases, the accuracy of the water clock will also decrease."
In this case, the variable you will change is the amount of water in the water clock. The variable you will measure is the clock's ability to measure time. At the end of the experiment you will examine the water's ability to keep time compared to the control.
Having a control experiment will help you isolate each variable and measure the changes in the dependent variable. Only one variable will change between the control experiment and the experimental water clocks, and that is the amount of water in the container. For the control experiment you will use a full container that will have level water pressure and time one minute. At the end of the experiment you will compare the one-minute markings with the markings of the experimental clocks.
What Are the Variables?
Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:
- The temperature of the water
- The size of the containers
- The size of the hole in the container
- The number of containers the water flows through
- The amount of water used
In other words, the variables in this experiment are everything that might affect the drip rate of the water. If you change more than one variable at the same time, you will not be able to tell which variable had the most effect on the water clock's accuracy.
Level of Difficulty
Moderate.
Materials Needed
- thumbtack or pin
- watch with second hand
- ruler
- water
- rectangular plastic container (roughly 1 gallon or 3.7 liters)
- cylindrical tall glass jar
- two chairs, with flat seats
- masking tape
- cup
- marking pen
Approximate Budget
$10.
Timetable
45 minutes.
How to Experiment Safely
This project poses very few hazards. Be careful with the thumbtack. If you are concerned about spilling water, place old newspapers on the floor under the area where you are conducting the experiment.
Step-by-Step Instructions
- Measure the height of the rectangular plastic container and draw a mark at the one-quarter, one-half, and three-quarters points.
- Use the thumbtack to punch a small hole in the bottom of the plastic container in the center. Position the container so that each side rests on a chair, with the middle open.
- Place the cylindrical glass on the floor directly beneath the hole.
- Hold your finger tightly over the hole in the plastic container and completely fill the container with water. Have a cup of water nearby to keep the container full as the water drips out.
- Take your finger off the hole and let the water drip out into the glass on the floor for 1 minute. While the water is dripping, refill the container with water so that it remains completely full.
- After 1 minute place your finger over the hole and empty the container in a sink. Place a piece of masking tape lengthwise along the cylindrical glass and draw a small line on the tape at the water level.
- Use the ruler to precisely measure the height of the water in the glass. This measurement equals 1 minute. From the 1-minute mark measure four more 1-minute marks. You should have five evenly spaced lines along the masking tape, one for each minute.
- Return the plastic container to its position on the chairs. Hold your finger over the hole and fill the water level to the one-quarter mark. Remove your finger and time how long the water takes to reach each of the marks on the tape. Do not put more water in the container. Note your results in a chart.
- Repeat the process with the starting water level at the one-half point and the three-quarters point. Note your results.
Summary of Results
Examine your chart of the times. Was your hypothesis correct? How did the starting water level at the one-quarter mark compare to the control minute? How did the times change as a result of the water level? Plot your results with the time on one axis and the starting water level on the other axis. Can you think of ways to make your water clock remain accurate? Write a summary of your results and conclusions.
Troubleshooter's Guide
Below is a problem that may arise during this experiment, a possible cause, and a way to remedy the problem.
Problem: The water ran out before it completes the five minutes.
Possible cause: The pinhole may be too large or your plastic container may not be large enough. Repeat the experiment, using a smaller pin or thumbtack. You could also shorten your time measurement, but the experiment works best if timed for at least three minutes.