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It’s summer here, and that means lots of swimming, splash pads, and water balloon fights. But what if I told you there’s a science lesson waiting for you in those water balloons?
This experiment compares an air-filled balloon to a water-filled balloon by holding each over an open flame. Since water has a higher heat capacity, it prevents the balloon from popping!
They won’t miss just a couple of water balloons in the name of science, right? So let’s find a flame and get to experimenting!
How to make the Balloon Heat Capacity STEM experiment
Supplies you will need
For this experiment, you will need the following:
Before you start
Please watch fingers around the open flame!
Instructions
Here is how to do this experiment with your child:
Step 1: Fill each balloon
In our experiment, we’re comparing an air-filled balloon to a water-filled balloon.
Blow up one of the balloons with just air. Fill the other balloon at least halfway with water. Set aside.
Step 2: Place a towel down
Just in case your water-filled balloon pops (it can only withstand so much heat!), it might be a good idea to put down a towel. Totally optional, but if you’re doing this inside, it might be a good idea!
Step 3: Hold each balloon over the candle
This part gets loud, so if you have sensitive ears in the room, warn them ahead of time!
Hold the air-filled balloon over the flame. It won’t take long for it to pop. You can even have someone time it to see how long it takes and compare it to the water-filled balloon.
Next, hold the water-filled balloon over the flame. What happens? Does it pop right away? What does the balloon feel like when you take it off the flame (touch where the water is)?
Since water has a higher heat capacity, it keeps the balloon from popping!
The STEM behind the Balloon Heat Capacity Experiment
This experiment teaches:
- Heat capacity
- Insulation
- Heat transfer
How it works
In this experiment, we’re comparing the heat capacity of water versus that of air.
When we touch the air-filled balloon to the flame, the rubber quickly heats up. Since air has a low heat capacity, it doesn’t absorb heat from the rubber. That causes the balloon’s rubber to weaken and burst from the internal air pressure.
When we touch the water-filled balloon to the flame, something cool happens! Water has a high heat capacity, which means it needs a lot of energy to raise its temperature significantly.
The heat from the candle is quickly transferred through the thin rubber of the balloon to the water. The water absorbs the heat, which in turn keeps the rubber from bursting.
Convection inside the balloon also helps distribute the heat away from where the candle touches the balloon, which helps even more.
Heat capacity
Heat capacity is a property that quantifies how much heat energy that something can absorb or release when the temperature changes. Some things can soak up a lot of heat without getting much hotter, while others get hot very quickly and absorb less heat.
In the case of our experiment, water has a higher heat capacity than air, so the water absorbs the heat from the candle a lot more efficiently than the air does, which makes our balloon not pop.
If you want to dive deeper into heat capacity, read on!
The water molecule is made up of one part oxygen and two parts hydrogen, and the oxygen and hydrogen are quite “sticky” to one another. That’s due to the slight positive charge of the hydrogen and the slightly negative charge of the oxygen (so they’re attracted to one another!).
That stickiness is called a hydrogen bond.
When we add heat to the mix, the heat energy has to first unstick all of those bonds before it can make the hydrogen and oxygen move around faster, which is what makes the water hotter.
Air, on the other hand, doesn’t have those bonds to break up before we can heat it up with heat energy. The heat just makes the molecules immediately start to move around faster, which makes the air hotter. They get super hot, super fast!
That’s why the water keeps the balloon from bursting (at least right away): the water absorbs quite a bit of heat away from the rubber and takes longer to heat up than air.
Insulation
Insulation refers to materials that are designed to reduce the rate of heat transfer between two areas of different temperatures. The goal of insulation is to slow down the flow of heat. That can either be keeping heat in or keeping heat out.
Think about oven mitts: they’re designed to protect your hand from the super-hot oven. Or, think about a thermos and how it’s designed to keep your hot beverage hot. Those are all insulation!
Insulation is made of materials that do not easily conduct heat. So materials with lots of free electrons are good conductors (metal) and materials where electrons are more tightly bound are good insulators (fiberglass, foam, wood).
In our experiment, the water in the balloon acts as an insulator, insulating the rubber from the flame’s immediate heat. The water is absorbing the heat and keeping the rubber cool enough to prevent bursting.
That’s all temporary though, since the water will eventually start to heat up and won’t be able to absorb the heat to protect the rubber.
Heat transfer
Heat transfer is the process of thermal energy moving from an area of higher temperature to an area of lower temperature. There are three modes of heat transfer: conduction, convection, and radiation.
Conduction is heat transfer through direct contact. Warmer, more energetic particles collide with the cooler, less energetic particles. When they collide, the warmer particles transfer some of their kinetic energy. In our experiment, this is the flame heating up the rubber of the balloon.
Convection is heat transfer through liquids and gases. In this case, when we heat a liquid or gas, it becomes less dense and rises. Then cooler, denser liquids or gases sink down, and it creates a circulation. That circulation carries thermal energy throughout the liquid or gas. In our experiment, the water inside of the balloon is circulating as it heats up. Here’s a great experiment where you can actually see the convection taking place!
Finally, radiation is heat transfer through electromagnetic waves (thermal radiation). Radiation doesn’t require a type of medium in order to be transferred. In our experiment, the thermal radiation is felt from the candle flame and directly hits the balloon.
More experiments with heat to try out with your child
- Convection in Action: Witness how temperature drives convection
- Fire vs. Fizz: Using carbon dioxide to extinguish a flame
- Crush a Bottle Using Thermal Contraction!
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