Pop It!
Scientific Method
Materials:
Bamboo skewer
Petroleum jelly or vegetable oil
2 balloons
Set-Up:
1. Coat the bamboo skewer with petroleum jelly or vegetable oil.
2. Place the materials in front of you.
Science Time:
1. Ask a member of the audience to be your helper.
2. Have the helper blow up one balloon and tie the end in a knot.
Make sure that the balloon is blown up completely.
3. Ask your helper to take the skewer and stick it through the balloon
without popping it. He or she will not be able to do it.
4. Blow up the second balloon to full size, but do not make a knot. Let
some air out of the balloon to reduce the size of the balloon by a
third. Tie the end of the balloon in a knot.
5. Place the sharp tip of the skewer on the end of the balloon
opposite the knot.
6. Spin the skewer slowly by rotating it back and forth between your
fingers. Slowly apply pressure to the skewer while continuing to spin
it until the tip of the skewer pierces the balloon’s surface without
popping it.
7. Continue to slowly push and spin the skewer through the balloon
until the sharp tip reaches the opposite side of the balloon near the
knot.
8. Keep applying pressure while spinning the skewer until the tip of the
skewer pierces the balloon surface on the opposite side, without
popping the balloon.
Tips:
This trick is difficult to do the first time. You’ll probably need to practice it
several times before the students. You may need to add more petroleum
jelly or vegetable oil to the skewer to make sure it doesn’t burst the
balloon.
You can also try placing a clear piece of tape on opposite sides of the
balloon. Poke the skewer through the taped areas of the balloon.
Explanation:
Balloons are made of rubber. You are able to pierce the balloon without
it bursting because of the unique composition of rubber.
Rubber is made of molecules in long chains. These long chains of
molecules are linked together crosswise, similar to a screen on a screen
door, to create the balloon. When your helper quickly pierces the
balloon, the chains break apart and the balloon bursts. However, when
you try very slowly to pierce the balloon, the chains of molecules push
apart slightly, making space for the skewer to pass through.
You make it easier for the skewer to pass through the chains when you
blow up the balloon and then reduce its volume. Blowing up the balloon
completely and then releasing the air weakens the chains of molecules in
some places. This allows the skewer to pass through the balloon more
easily. The petroleum jelly also helps by serving as a lubricant, which is a
film like substance that reduces friction between the solid surfaces. The
jelly reduces the friction between the skewer and the balloon, allowing
the skewer to pass though more easily.