# Water clock Science Project

Bernard Gitton's Time-Flow clock
Luna04 / CC-BY-SA-3.0, via Wikimedia Commons

### Purpose

To build a feedback-controlled system (a water clock) and research ways to improve the system design.

### Context

This activity should follow student encounters with more simple systems, such as pencils, scissors, etc. In this activity, students will begin to examine more closely the interactions between the parts of a system. The main goal of having students learn about systems is not to have them talk about systems in abstract terms, but to enhance their ability to attend to various aspects of particular systems in attempting to understand or deal with the whole system.

### Motivation

Begin by letting students view This Week's WOW: Water Clock, a video of the largest water clock in North America, on display at the Children's Museum of Indianapolis. Students should jot down and describe some of the parts that make up the water clock.

• What are the parts of a water clock?
• (An oscillator [the pendulum], a frequency divider, a minute counter [the minute discs], and an hour counter [the hour balls]. Water from a pump in the basement, just below the clock, is pumped through a pipe running up the middle of the clock into a reservoir at the top. The water then drips down onto a scoop at the top which is connected to the green, swinging pendulum. The pendulum causes the scoop to dump the water into a series of siphons. The siphons fill and empty into the minutes' globes. A siphon is a tube in an inverted "U" shape which causes the solution to flow up, without pumps, powered by the fall of the liquid as it flows down the tube under the pull of gravity.)
• What is it designed to do?
• What advantage does it have over other devices such as sundials?
• (It could be used at night as well as in daylight.)
• What is the largest problem associated with water clocks?
• (The rate of flow of water is very difficult to control accurately.)
• Discuss the answers with the class.

### Development

How A Water Clock Works
In the first part of the activity, the class will investigate how a water clock works and the effect of one of its variables on its ability to be an accurate timepiece.

Tell students: Early water clocks were stone vessels with sloping sides that allowed water to drip at a nearly constant rate from a small hole near the bottom. Other water clocks were bowl-shaped containers that slowly filled with water at a constant rate. Markings on the inside surfaces measured the passage of time as the water level rose on the inside of the bowl, a result of its slowly sinking. We're going to use a soft drink bottle to make a similar device.

Ask students to select what they consider to be the most important parts of the device.

Procedure
Do the following as a teacher-led exploration:

1. Use the pin to make a very small hole in the bottom or close to the bottom of the bottle. A hole smaller than the diameter of the pin is desirable. Let the students examine the hole.
2. Holding a finger over the hole, fill the bottle with water to a level just below the shoulder where it begins to have a smaller diameter. Mark this level on the outside of the bottle. Measure the time required for 100 ml (+/- 0.5 ml) of water to run or drip out of the bottle. Repeat the experiment with the starting water level about halfway up the bottle and with the starting water level very low in the bottle. Plot the times as a function of the distance the starting water level was above the hole in the bottle.

Discuss the results with the class using questions such as the following:

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