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All right, guys, it's now time for a cue card review.

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What is buoyancy-induced convection?

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What is the relationship between density and volume?

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What is the trend in the density versus temperature graph?

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Okay, did you get all that? Let's go visit Dan Giroux in his web domain.

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Hi, and welcome to my domain.

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NASA Connect has created a really cool web activity to help you understand apparent weight

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and to see how astronauts in outer space feel weightless.

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We also have a second activity to help you make an important elevator design decision.

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First, be sure you have the Squeak plug-in.

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It can be downloaded at www.squeakland.org for easy installation.

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Once you have the Squeak plug-in installed,

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you can access the activity at the NASA Connect website under Dan's domain.

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This activity is designed for use by students, teachers, and parents in the school or home setting.

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Now, you're ready to start the activity.

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On this site, Norbert and Zahid are waiting in an elevator for you to investigate what happens

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when you accelerate the elevator.

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If you're the hands-on type and want to try it out on your own first,

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read the brief directions along the left side of the screen

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and start by trying to make Norbert and Zahid weightless.

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Then you should read the book on the right side of the screen

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for important definitions, brief interactivities,

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explorations you should do, and challenges you should consider.

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If you want more directions before you start,

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begin by reading the book starting with the first page

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and click the little right arrow at the top center to go on.

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To help you get a head start, velocity is the distance traveled divided by the time it takes.

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If the elevator moves Norbert and Zahid downward,

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we will say their velocity is a positive number.

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To accelerate is to change the velocity.

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If you increase the velocity in the downward direction,

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we will say the acceleration is a positive number.

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Then, if you increase the velocity in an upward direction,

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the acceleration will be a negative number.

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Positive and negative numbers are essential to describe motion.

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Have fun, and explore!