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Title: Fire-Resistant Balloon
Principle(s) Investigated:
- This experiment demonstrates how heat can be transferred from one surface to another by thermal conduction
- Emphasizes the relatively high heat capacity and specific heat of water as compared to those of air. Water placed inside a balloon will absorb the heat from a candle flame preventing the balloon from popping
2. Energy can be transformed within a system or transferred to other systems or the environment.
6.2.3.2.3 Describe how energy is transferred in conduction, convection and radiation.
2. Substances can undergo physical changes which do not change the composition or the total mass of the substance in a closed system.
6.2.1.2.3 Use the relationship between heat and the motion and arrangement of particles in solids, liquids and gases to explain melting, freezing, boiling and evaporation.
Materials:
- Balloons
- Water
- Selected Liquids
- Matches or Lighter
- Candle
- Safety Goggles
Procedure:
1. Challenge the audience by saying there will be a competition to see whose filled balloon will last the longest (without popping) over a lit candle.
2. Choose two "cool" students to challenge you, the "coolest" teacher.
3. Ask the two participants from the audience to come up front.
4. Open the pack of balloons, the instructor picking the first balloon, which has the 25 mL of water previously placed in it.
5.Hold the balloon by the neck so that the main body of the balloon and mass of the water is concealed in the palm of your hand.
6. Then have each student select a balloon.
7. Teacher and students blow their balloon up to equal size (8-10 inches in diameter) and tie the end of their balloon with a knot.
8. Light the candle that is on the ring stand platform.
9. Place each student's balloon on the ring. They will pop very quickly. The audience can be the judge of the competition and count how long it takes for the balloons to pop.
10. Place your balloon on the ring. It should not pop for about 2-5 minutes.
11.Ask the students to explain the results. Why is the teacher the "coolest"?Results can be related to properties of water in the balloon, especially its high heat capacity.
Student prior knowledge:
Thermal conduction is the ability of a medium to allow heat to be conducted through it. The heat will always travels from a hotter spot to a cooler spot. For example, if one end of a metal rod is heated up, the heat will gradually travel to the other end until the entire rod becomes hot. Thermal conduction exists in solids, liquids and gasses. The conduction of heat through a medium happens because the particles in the medium vibrate or move faster when heat is applied to it. This vibration or movement of the particles will start at the point where the heat originates.
Explanation:
Water has a high heat capacity. In other words, it takes a lot of heat and energy to change the temperature of water by 1oC. The high heat capacity of water is due to the fact that it takes a lot of energy to separate water molecules (the bonds are very strong). Water has a heat capacity about four times that of air. This means that it takes about four times as much heat to raise the temperature of a balloon full of water than it would a similar sized balloon filled with air.
As the water-filled balloon is put on the flame, the heat of the flame is easily absorbed through the balloon and into the water. The water directly above the hot spot rises, cools, and sinks again, carrying away the heat from the hot spot (this cycle is called a convection current). In other words, the thin rubber surface that is being heated is cooled by the comparatively large volume of water above it. This cooling process continues until either all of the water in the balloon becomes too hot, or until a far more concentrated source of heat, such as a blowtorch, is applied to one small area on the balloon,
When an air-filled balloon is placed in a flame, it bursts. Air is a relatively poor conductor of heat away from the thin layer of rubber. As a result, the rubber overheats and the molecular bonds holding the rubber polymers together are broken.
Normal air molecules
Heated air molecules
Questions & Answers:
1. What makes the balloon pop when there is no water in it?
The reason a balloon filled with air pops when you put it over a flame is because the rubber of the balloon gets very hot and weak and then breaks.
2. What prevents the water balloon from popping?
When you fill a balloon with water instead of air, the water absorbs most of the heat, so the rubber doesn't get very hot. Water has a very high heat capacity, much higher than air, so it will keep the balloon from bursting.
3. Does the rubber have anything to do with this reaction to fire?
Yes, balloons will burst from fire since fire weakens the rubber and causes it to explode
Applications to Everyday Life:
Cars-Water is very effective when acting as a cooling agent in engines. A water pump circulates the water around the engine, and the heat produced by the engine is absorbed by the water. The hot water that circulates around the engine walls is then forced into the cars radiator where the heat from the water is released through the cooling fan.
Earth-The amount of energy required to vaporize water is almost six times again what is needed to heat it from freezing all of the way to boiling. This is why the Earth is a habitable planet: water evaporates from the oceans, carries it up into the upper atmosphere where it condenses out and falls back to the surface, but the water vapor condenses to form clouds and rain, it leaves the heat from the oceans up in the upper atmosphere where it radiates away into space. This effect controls the temperature of the Earth so that it is within the range in which life is possible: add more energy in,the water cycle just dumps it right back out.
Sweat- Your body uses water to control heat, when you exercise you drip "sweat" from certain parts of your body. Your body is actually using the water in your sweat to control your internal temperature so you don't get overheated.
Lava Lamps- You see convection currents within lava lamps. In lava lamp the coloured oil is heated by a light and then rises, to eventually cool and fall back to where it started, only to repeat the process again. Convection currents are incredibly important in our weather systems and ocean currents.
Photographs:
Videos:
http://www.youtube.com/watch?v=VDEL9bxXSls
http://www.youtube.com/watch?v=XVvPsSBZ7dY
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