A balloon flinker is a fun thing to create if you happen to have some birthday party balloons just floating around the house. The idea is to add just enough weight to the balloon to balance out the lifting force of the helium gas in the balloon.

What you need:

• Helium balloon with ribbon attached
• Paper clip
• Small metal washers or pieces of paper

What to do:

1. Tie the balloon’s ribbon to the paperclip.
2. Thread several washers or pieces of paper onto the paperclip. What happens when you let the balloon go?
3. How can you make the balloon FLINK – neither float nor sink? Try adding more washers or pieces of paper…or taking some away.
4. Keep changing the design of your flinker until it flinks for 10 seconds.

What’s the science?
Gravity is pulling down on your balloon, the helium inside the balloon, and on the air around the balloon. The helium inside your balloon is a gas, just like air. But helium weighs less than air. So a balloon filled with helium weighs less than the air around it. The air around the balloon pushes up the balloon harder than gravity pulls down, so the balloon floats to the ceiling. If you add weight to the balloon, you make the balloon heavier. Too much weight means that gravity pulls down harder than the air pushes up, so the balloon sinks to the ground. If you add the right amount of weight, the balloon will flink – it doesn’t float or sink.

What will happen if . . .

• you change the length of the ribbon?
• you use a balloon filled with more (or less) helium?
• you add different materials to the paperclip, like popcorn, another paperclip, or a styrofoam packing peanut?

Choose one thing to change (that’s the variable), and predict what you think will happen, then test it.