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Rubber Bones

In this activity, students see that without calcium, bones become floppy.

Although bones in museums are dry, hard, brittle or crumbly, the bones in your body are very different. They are alive, growing and changing all the time like other parts of your body.

Bones have 2 main components:

  1. Inorganic compounds ~70%. Primarily Apatite : a hard mineral that contains calcium and makes them stiff.
  2. Organic compounds. ~ 30%. Primarily Collogen: a rubbery protein component that makes them strong.

Stiffness is an indicator of the ability of a bone to remain in/return to an original form after being subjected to a force. 

Strength measures how much stress can be applied before a bone deforms permanently or fractures.

If you leave bones in a warm place for a long time, they get brittle because the collagen decomposes or dries out, losing it's "rubbery" flexibility (that's why you have to let a wishbone dry before trying to snap it).

Leaving bones in an acid like vinegar will dissolve the apatite out of the bone, making them floppy.

Use this demonstration to show what would happen if your bones didn't contain calcium.

FunFact: The furcula ("little fork" in Latin) or wishbone is a forked bone found in birds and some other species of dinosaurs, and is formed by the fusion of the two clavicles (collar bones).


  • Describe the main components of bones.


  • Per Demo:
    chicken bones, cleaned of any meat and washed  SAFETY TIP: for health reasons please use pre-cooked chicken bones

Key Questions

  • What are the main components of bone and what do they do?

What To Do

  1. Soak chicken bones in vinegar for at least 24 hours. Soaking them for a few days will give an even better effect.
  2. Pass the bone around the class, letting students feel the difference between a regular bone and the vinegar-soaked bone.


  • Experiment to determine whether:The length of time the bone is in vinegar affects the bendiness (refresh the vinegar after a couple of days for best effect). Smaller or larger bones become bendy at different rates. Different vinegars give different results.You can do the same with a hard-boiled egg.
  • Experiment to determine whether:Different vinegars give different results.
  • Experiment to determine whether:Smaller or larger bones become bendy at different rates.