Experimental VariablesLast week we talked about designing a rocket to have only one variable so that we could determine what factors affect rocket flight and perhaps how. This week we talked about experimental variables.
Experimental variable: An aspect of an experiment which changes during the course of the experiment.
In order to avoid flaws in an experiment, one must be able to recognize experimental variables and control them. By comparing the results of exprriments when different experimental variables are changed is often the only way a scientist will learn something from an experiment.
|A Floating Egg?|
Analyzing the Floating Egg Experiment
You can examine the Floating Egg experiment as an example of the importance of avoiding variables in experiments. We know that it was the addition of salt that changed the way the egg acted because we did not vary anything else in the experiment except the salt. The egg, the glass and the water all stayed the same. The importance of the impact of variables on experiments increases with how complicated the experiment is, but "you should always reduce the number of experimental variables that are not a necessary part of the experiment..because the effects on the experiment are not always predictable." -Exploring Creation with General Science, by Dr. Jay Wile
We looked at each of the students' rocket designs in terms of variables. Once their rocket designs were approved, we could begin to build the rockets, but first we analyzed the results of the balls experiment we did last week. We recorded the results of the ball tosses, and averaged the results. As we averaged the measurements, we looked for any measurements that were obvious mistakes that should be ignored. The measurements were then averaged, according to Team A's and Team B's results. Using the data sheets from here, we drew a line from the corner of the grid through the number of degrees measured by Team A and extended the line to the edge of the page. We did the same in the opposite corner with Team B's results. We next drew a horizontal line from the top of the triangle across to the side of the page to find the height the ball traveled. The results of the two ball tosses can be made into a bar graph.
Building Model RocketsOnce we finished this exercise, we could begin building the rockets. Here are the steps we followed.
Prepare spacer and glue stick. Use a pencil to mark the engine spacer tube 1/4 inch from the end. Take a coffee stirrer and mark it 2 1/4 inches from one end. If your rocket design requires you to shorten the body tube, do that with a knife or scissors now.
Glue in engine block ring. Use the glue stick to smear a drop of glue 2 1/4 inches inside the tube, making sure that you do not get any glue near the end of the tube or on the engine block ring. Place the engine block ring just inside of the end of the tube.
Push in the engine block ring with the spacer tube up to the 1/4 inch mark. Slide in with one motion. Remove spacer tube immediately or it will get stuck. Roll the tube on a hard surface so that the ring makes good contact with the glue.
Attach shock cord to body tube. Draw a straight line down from the top end of the tube (opposite the engine block ring) one inch long.
Use scissors to cut a slit along the line. Slide the end of the rubber shock cord into the slit and...
tape the short end to the outside of the body tube.
Mark tube for number of fins you want. This will depend on your plan you have already created. You could have 3, 4 or 5 fins. You can use a door frame as a straight edge to mark the lines on the tube.
Smear a tiny bit of glue all along the fin edge and press onto tube along marked lines. Glue all fins in place. Make sure fins are straight until glue is dry, which should take about 10 minutes.
Tie the end of the shock cord securely to the nose cone insert. Trim the end of the knot closely and add a drop of glue to the knot to secure it. Do not glue the nose cone together yet.
Leave these to dry.
Leave these to dry.
sources and resources:
- Experimenting with Model Rockets GEMS Teacher's Guide
- Height-O-Meters GEMS Teacher's Guide
- Exploring Creation with General Science, Jay Wile