Our Experiments

Hello from Houston! It's hot down here ... but cooler, I hear, than it is back in New Jersey. We're having a blast, working hard, and getting ready for our flight. We got an unexpected bonus yesterday when the astronauts from the final shuttle mission came to Houston for a thank-you reception here at NASA's mission control.

About our experiments:

Our first experiment is a simple pendulum, which we made out of a softball hanging on a V of string (so it would swing along the same arc throughout the flight). The pendulum should swing faster as gravity gets stronger at the bottom of each parabola and slower as gravity decreases. During weightlessness at the top of each parabola, the pendulum should stop swinging and the string should go slack. We have a videocamera to record the pendulum’s motion and a motion detector (like what we use in physics classes) to keep track of how far and how fast the pendulum is moving each time it swings. Physics teachers often use a pendulum in class as an example of an oscillation, but very few of us have gotten the opportunity to run a pendulum experiment with gravity as a variable, a ‘knob’ to turn during the pendulum’s swings.

Our second experiment is also an oscillator like the pendulum, only the repetitive motion will be in the vertical direction. We will hang a mass from a spring and set it bobbing up and down. Unlike the pendulum, the mass-on-a-spring should oscillate in exactly the same way no matter what the value of gravity is. But: the midpoint of its oscillation should rise as gravity’s value decreases and fall as gravity increases. We will use a video camera and motion detector to record the motion of the mass-on-a-spring.

The third – and coolest – experiment is on blowing bubbles … soap bubbles, like what we all used to have a blast playing with as kids. We’ll be videotaping their behavior and measuring their lifetime as the value of gravity varies during the flight. The idea here is that what usually makes bubbles pop – here on the ground – is that the soap solution drains to the bottom of the bubble, leaving a thin patch of soap film at the top of the bubble, at its ‘north pole’. When the bubble pops, the pop begins at that spot at the bubble's north pole where the soap film is thinnest and weakest. In a weightless environment, by contrast, there’s no reason for the soap film to drain anywhere, so we think the bubbles will last much longer. Along the same lines of reasoning, we think that the bubbles will have shorter lifetimes at the bottom of each parabola when gravity is stronger. We constructed a clear plastic ‘bubble box’ to run this experiment, and we equipped it with two bubble ‘guns’ – the Crayola kind from a toy store – outfitted with an electric motor so that once we started it going, it would keep pumping out bubbles until we stopped it. Two videocameras will record the behavior and evolution of the bubbles. In the photo, the motor is the gray box with the wires leading to it. We experimented with a lot of different bubble solutions, and we ended up going with a simple Dawn+water mix.

Here's our entire apparatus, viewed from below:

We built it in an open metal frame so that the entire setup would be both strong and light. The softball made a great pendulum both because the motion detector can 'see' it easily and because it shows up well on video. The videocamera for the mass-on-spring is above the softball.

They're keeping us really busy down here in Houston with pre-flight stuff. We're still on schedule to take our experiment weightless on Tuesday morning.