My school science team wanted students to explore how changing one variable can influence an experiment. This activity was designed to allow students to experiment by changing one variable. Students were allowed to decide what water volume and how many drops of soap they would use. Students created their soap solutions and after blowing bubbles were allowed to add a variable to attempt to create the largest soap bubble.
Results were very interesting. Students requested and added one of the following substances: salt, sugar, vinegar, glue, or baking soda. (Students identified each item used and I just got them out of a cabinet.) Students carefully measured each bubble blown to determine what the diameter was. Our largest soap bubble came in at a whopping 45 centimeters!
One of my favorites is paper helicopters and flight time. The paper helicopter activity has been around for a long time, but I turn it into a competition (like blowing the biggest bubble). In this case, we have a paper helicopter tournament: longest flight time wins. Prior to the tournament, the students work in teams to identify variables that could increase the flight time of the basic helicopter design. Each team picks one variable to test and then reports to the rest of the class. After reviewing each of the presentations, the teams make helicopters for the contest. The winning helicopter represents my home room agains my team teacher's class (so, in the end, it's actually a set of teams working together against the scientific work of another set of teams).
Variables included wingspan, body length, paper type, design, propellor angle, and method of release.
Another tried and true acitivity for testing one variable at a time is the period of a pendulum. Again, I turn it into a contest between two classes: after presenting and reveiwing each of the classroom teams' experiments, the teams build a pendulum clock: closest to 5 swings in 5.00 seconds (avg period of 1.00 sec) wins.
for first grade, we discuss controlled variables within planting (e.g., sunlight and position near sunlight and/or amount of water provided) to consider growth and other outcomes and ramp incline and position to discuss acceleration. i don't always conduct full investigations, but items like these always come up, for discussion, at least.
I think the level of variable you are using with your first grade students is very appropriate. Helping these young minds recognize water and light are variables is HUGE! I think we would have a much more scientific literate nation if more teachers recognized such important principles.
In class we make swingers (pendulums). String (all students work in pairs), paper clip, and a penny. First all string is measured the same so that students will have a standard. They discover how many swings it makes in a set time. Our standard is: Same length of string, one penny, release position at 90 degrees, amt. of swings in a set amount of time. With that set they start to change a variable. They always want to add another coin. They find nothing changes. Next we release from a different position, nothing changes, Then they decide they will change the length of the string, which does affect the outcome. Students love doing this. We then do a picture graph.
I see this as a great discovery activity because of the outcome differences between variables. I have a couple of questions about your swingers:
We make a loop on the end of the string then we tape a pencil onto the desk, so that it hangs over about 3 inches. Sometimes depending on the length of the string we have the pencil taped to the top of lockers. We loop the string over the end of the pencil. The string is then pulled directly parallel to the desk. I monitor the clock. I say "release" and the students count a full swing (to one side and back) as one. They must count silently and both students count to check the answer with each other. When I say stop, they must stay with the whole swing number (not 9 1/2 swings). I believe it is always 12 or 13 swings in 15 seconds. I have students who think if the hold the sting straight up it will make a difference, they really enjoy the investigative part of it. We do three trials so they see that it is basically always 12 or 13 swings. It is very hard to not give hints but that is one of things you learn when doing the higher order thinking activities. I just lead them and let them think they are coming up with all the wonderful ideas!