In this activity you will design and test a method to measure the rate at which a siphon lets water flow out of a bottle, that will let you answer the question, "Does water in a siphon always flow at the same rate? "

Materials needed: siphon system including at least one container with straight sides and one with a wide opening so that its easy to atch the flowing water in it. You may also find useful a ruler and/or meter stick, masking tape or paper strips, rubber bands, cup or container marked in units of volumes, clock with a second hand.

Here are some methods that various groups have tried:

1. If the container is a cylinder, the amount of liquid in it is proportional to the water level. Then you could make marks on a strip of paper or tape on the side of the bottle, to indicate the water level at equal time intervals (for example, 30 seconds).
2. You could start with evenly space marks along the side of the bottle and record the time at which the water level reaches each mark.
3. You could catch the water coming out in a small measuring cup, and time how long it takes to fill it
4. You could catch the water in a measuring cup, and determine how much comes out in a small interval of time, like 10 seconds.

Another issue to be decided is what to with the water that drains out. You could use it to fill up another container, or you could fix the outlet end of the tube at a certain height and let it run out that way.

Since these different methods measure different things, they have to be analyzed slightly differently, too

Diagram and describe the method you will use, and explain how what you measure is related to the flow rate.

Then do the experiment to answer the question, Does water in a siphon always flow at the same rate? Explain how your method answers the question.

Check the box when you are done:  

Next:More about siphons