Education and
Public Engagement
at the Lunar and Planetary Institute
Health in Space

Space Stations - Bones of Contention


Children make models that represent bones on Earth and bones that have been in space by poking holes into foam cups. They press down on each of the two bone models to discover that exercise and nutrition make for stronger bones.

Activity Time

5 minutes

Type of Program

Facilitated hands-on experience
Station, presented in combination with related activities
Passive program
Demonstration by facilitator

Intended Audience

Families or other mixed-age groups, including children as young as 4 years old with assistance from an older child, teen, or adult
School-aged children ages 5–7 and 8–9
Tweens up to about age 13

What's the Point?


For the facilitator:

For Each Group of 15 Children



1.  Share ideas and knowledge.

Earth’s gravity still affects the space station and the astronauts, but since they are continually falling around the Earth (i.e., orbiting), they constantly experience that free-fall feeling we occasionally experience on amusement park rides. Astronauts aren’t riding a roller coaster, though; they are riding the International Space Station at 17,500 miles (28,000 kilometers) per hour, 200-250 miles (about 320-400 kilometers) above the Earth! Since the astronauts, their food and supplies, and their spacecraft are all falling together in orbit around the Earth, everything appears to float.

Use the terms “free-fall” and “microgravity”; the terms “zero gravity” and “weightlessness” are don’t give an accurate impression about how gravity works in space.

With older children, explain that the free-fall environment that astronauts experience in space is called microgravity. As they orbit Earth, the effect of gravity is so small (“micro-“), that it does not matter that a feather, a person, and a spacecraft all have different masses (i.e., are made up of different amounts of matter).

2.  Model a healthy bone on Earth and an astronaut’s bone after living in space.
Encourage each pair of participants to take turns with the following steps:

  1. Take 2 Styrofoam cups and a slightly sharpened pencil or pointy stick. Styrofoam cups
  2. Poke about 5 holes, scattered randomly, in one foam cup, and poke about 25 holes in the other.
  3. Label the cup with 5 holes “Bone on Earth” and the cup with 25 holes “Bone in Space.”
  4. Compare the models of the bone on Earth with the bone in space.
  5. Stand each of the “bones” (cups) upright on a flat surface.
  6. Place your hand, palm down, on top of the Earth bone. Gently press down and observe whether it is difficult or easy to crumple.
  7. Gently press down on the “space bone” and observe how difficult or easy it is to crumple.

3.  Compare observations and connect them to the “real world.” Prompt the children to compare their experiences pressing down on each of the “bones” with other children and/or family members. Prompt them to connect that experience to what astronauts experience in space.

4.  Explain that in space (a microgravity environment), astronauts’ bones become weak. Their muscles don’t have to work as hard, and the muscles don’t have to pull as hard on the bones to support the astronauts’ bodies. The “space bone” hadn’t gotten enough exercise, and it lost minerals and became weak. Astronauts must exercise almost two hours each day and get a diet rich in calcium to help keep their bones from getting too weak until they return to Earth.

It is important to emphasize that being in space does not put holes in your bones. This activity uses models of bones (cups) to demonstrate the effects of mineral loss in bones as a result of being in space. The “bone” (cup) with more holes models a bone that is less healthy than the “bone” (cup) with fewer holes.

5.  Conclude. Summarize that kids and adults on Earth also get weaker bones if we don’t eat a well-balanced diet and exercise enough. Challenge the children to eat a balanced diet and exercise to keep their bones from becoming like “space bones.”


Weightlessness Demonstration
This Windows to the Universe® activity outlines facilitator steps to illustrate the effects of free fall using cups and water. Appropriate