CYGNSSWhich Way is DOWN??



Astronaut Mark Lee participates in an extravehicular activity (EVA). Credit: NASA


All physical objects are attracted toward each other by the natural force called gravity, but the effects of gravity that we observe can sometimes be misleading. For example, objects that are revolving around Earth in orbit appear to be weightless and we sometimes use the terms "zero-g" or "zero gravity" to describe this observation. Such descriptions often lead to the false belief that these satellites have escaped Earth's gravity, but this is not true! All objects near Earth, regardless of size, speed, or altitude, experience the downward force of gravity toward the center of the Earth!



bookYou will need: a book and piece of paper of roughly the same size.

  1. If you drop the book and the paper, laying flat side by side, from around 12 inches above a table, which do you think will reach the table first? Write down your prediction on the paper, then try the experiment.
  2. What happened? Was your prediction correct? Write down your results.
  3. What will happen if you try the experiment again, but this time with the book stacked on top of the paper? Write down your prediction and test it out.
  4. Were the results different this time? Write them down, as well.
  5. Finally, what do you think will happen if you stack the paper on top of the book, and drop them a third time? Write down your prediction and give it a try!
  6. Were you correct, this time? What do you think happened?
  7. What other forces might have been at work during these experiments? Would the results be different if you dropped the items from a higher point?


Check out these videos for a closer look at gravity near space!


    Felix Baumgartner prepares for a high altitude skydive! Credit: DailyMail



    The International Space Station as seen from above. Credit: NASA



    The CYGNSS satellite mission. Credit: SWRI


  1. GOING DOWN, ANYONE? The force of gravity is the focus of this demonstration using a ruler, string and a paper clip. Students observe that the Earth's gravity is always downward toward the center of the Earth.
  2. 3-2-1 BLAST OFF Students understand how satellites are placed in orbit by launching marbles into space, using two plastic rulers and clay. They describe the forces that determine the trajectory of flight.
  3. MOONS, RINGS, AND RELATIONSHIPS In this gravity activity, learners will design their own experiments to explore the fundamental force of gravity and then extend their thinking to how gravity acts to keep objects like moons and ring particles in orbit. They use the contexts of the solar system and the Saturn system to explore the nature of orbits. The lesson enables students to correct common misconceptions about gravity and orbits and to learn how orbital speed decreases as the distance from the object being orbited increases.