Chloe Adams
The “rising water” or “upside-down jar in water with a candle” experiment is a popular way to learn about air pressure. It involves placing a burning candle in a dish of water and covering it with an inverted jar. As the flame goes out, the water level inside the jar rises. This experiment has been used to introduce the concept of pressure and the role of oxygen in combustion. While some attribute the rising water to oxygen depletion, others suggest it is primarily due to changes in air temperature and pressure. This classic demonstration sparks curiosity and provides an opportunity to explore the underlying scientific principles at work.
| Characteristics | Values |
|---|---|
| Objective | To demonstrate how air pressure changes when a candle inside an upside-down jar placed in water is lit and then extinguished |
| Materials | Candle, jar or glass, plate, water, matches or lighter, food colouring (optional) |
| Setup | Place the candle in the middle of the plate and fill the plate with water. Light the candle. |
| Experiment | Quickly turn the jar or glass upside down and place it over the lit candle. |
| Observation | The flame goes out, and the water level inside the jar rises. |
| Explanation | The candle flame heats the air in the jar, causing it to expand and some air to escape. When the flame goes out, the air inside the jar cools and contracts, creating a vacuum due to low pressure inside and high pressure outside the jar. This pressure difference causes the water to be pushed up into the jar. |
| Variables | Size of the jar, temperature of water, size of the candle |
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What You'll Learn
The experiment setup
Step 1: Prepare the Plate
Start by preparing a flat plate. You can add a small amount of water to the plate, ensuring it covers a wide enough area. This water will be used for the experiment. If desired, you can add a few drops of food colouring to the water to make it more visible and exciting for younger participants.
Step 2: Create a Platform for the Flame
The next step is to create a safe platform for your flame. You can use a candle for this experiment. Place the candle in the middle of the plate, ensuring it is secure and will not tip over. If you do not have a candle, you can get creative. One option is to use a cork bottle stopper with a wooden end. Cut the cork in half lengthwise and poke holes in it to hold matchsticks upright. You can also use a small block of wood with holes drilled into it, ensuring it floats in the water.
Step 3: Light the Flame
Using a match or a lighter, carefully light your chosen flame device. If you are using matches, you will need to act quickly before they burn out. With a candle, you have a little more time.
Step 4: Prepare the Jar
Now, grab a jar or a clear glass. It is important that the jar is large enough to create an enclosed space. Gently but quickly, turn the jar upside down and set it over the burning flame. Ensure the jar is resting on the plate and not directly on the flame.
Step 5: Observe
At this point, you will witness some fascinating science in action! You will notice that the flame eventually goes out, and the water level inside the jar begins to rise. This happens because the hot air inside the jar expands and escapes, and when the flame goes out, the air cools and creates a low-pressure system. The high-pressure air outside the jar pushes the water in, forcing it to rise.
Step 6: Optional Variations
You can experiment with different variables to observe their impact. Try using hot or cold water instead of room temperature water. You can also vary the size of the candle or use multiple candles to see if the size of the flame affects the water level.
Remember to exercise caution when handling flames, and always have adult supervision for younger participants.
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Lighting the candle
The next step is to light the candle or matches. If you are using matches, you will need to hurry onto the next step before they burn out. If you are using a candle, you can take your time.
Once the candle is lit, grab your jar or clear glass and gently, but quickly, turn it upside down and place it over the flame. The jar may get a little hot, so be careful. The flame will go out, and the water will rise in the jar.
The reason the water rises is due to a change in air pressure. The candle flame heats the air in the jar, causing it to expand. Some of this expanding air escapes from under the jar. When the flame goes out, the air in the jar cools down and contracts, creating a vacuum. The high-pressure air outside the jar then pushes the water into the jar to equalise the pressure.
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Inverting the jar
To begin the experiment, you will need to light the candle and place it in a dish of water. The candle can be stuck onto the middle of a plate, and then the plate can be filled with water. It is important to ensure that the candle has a safe platform to float on in the water. If matches are being used instead of a candle, you can cut a cork in half lengthwise and poke holes in it for the matches to fit, or use a small block of wood with holes drilled into it.
Once the candle is lit and placed in the water, the jar or glass should be gently but quickly inverted and placed over the flame. It is important to act quickly if using matches, as they will burn out faster than a candle. The jar should be large enough to cover the flame and rest on the plate.
As the flame burns, hot air expands inside the jar. When the flame goes out, the air inside the jar cools and contracts, creating an area of low pressure. Simultaneously, the pressure outside the jar remains constant. As a result, the high-pressure air outside pushes the water into the jar to equalize the pressure, causing the water level inside the jar to rise.
The inversion of the jar is a critical step in the experiment as it traps the hot air produced by the flame. This allows for the observation of the pressure changes that occur as the air cools and the resulting rise in the water level. By inverting the jar quickly, the experimenter can capture the hot air and observe the dynamic interplay of pressure and temperature that leads to the water being "sucked up" into the jar.
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The science behind the rising water
The rising water experiment is a fun and simple way to learn about air pressure and combustion. It involves placing a lit candle in a plate of water and then covering it with an upside-down jar. As the flame goes out, the water is seen to rise inside the jar. But why does this happen?
The key to understanding this phenomenon lies in the concept of air pressure and how it changes with temperature variations. When the candle is lit, the flame heats the air inside the jar, causing it to expand. Some of this hot air may escape, creating a slight vacuum effect. However, the primary factor at play here is the temperature change when the flame goes out. As the air inside the jar cools down, its pressure decreases, creating an area of low pressure within the jar. This is because the molecules slow down and exert less pressure on the water surface.
Simultaneously, the air outside the jar maintains a higher pressure due to the constant atmospheric pressure. This pressure differential results in the water being pushed up into the jar by the higher-pressure air outside. The water continues to rise until equilibrium is reached, and the pressure inside and outside the jar equalizes.
It is important to note that while oxygen depletion due to combustion may play a minor role in the water rising, it is not the primary cause. The rapid rise in water level occurs when the candle dims and goes out, indicating that temperature changes have a more significant impact. Additionally, the chemical process of combustion and the physical process of temperature change interact, initially cancelling each other out, which makes their individual effects more challenging to detect and distinguish.
The rising water experiment is a fascinating way to visualize the fundamental principles of air pressure and temperature's influence on it. By observing the water's behaviour, we gain a tangible understanding of these scientific concepts.
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The misconceptions
A common misconception about the experiment involving an upside-down jar, water, and a candle is that the consumption of oxygen inside the jar is the primary cause of the water rising. However, this notion has been challenged. The water does not rise immediately; it rises only after the candle dims and goes out. If the consumption of oxygen were the sole factor, one would expect to see a steady rise in the water level from the beginning of the experiment, rather than a rapid rise at the end.
The truth is that there are two main effects at play: the chemical process of burning and the physical process of temperature change. These two effects initially cancel each other out, making them more challenging to detect. The temperature change due to the burning candle appears to be the more significant factor. As the candle burns, the air above it becomes hot and less dense than the surrounding air. When the jar is placed over the candle, the hot air is trapped inside. As the flame goes out, the air inside the jar cools down, causing the pressure inside the jar to decrease.
Another misconception is the presence of bubbles during the experiment. While some sources mention the presence of bubbles, others claim that if the experiment is done correctly, no bubbles should be observed. This discrepancy may be due to variations in the experimental setup or the accuracy of observations.
It is worth noting that the size of the jar used in the experiment can also affect the results. A larger jar may lead to a smaller effect, as only part of the room will be affected by the temperature and chemical changes. Additionally, reducing the space above the candle can help isolate the impact of the chemical process and temperature change, potentially leading to more pronounced results.
In conclusion, while the consumption of oxygen does play a role in the experiment, it is not the sole or primary cause of the water rising. The temperature change and the resulting pressure difference are the key factors influencing the water's behavior.
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Frequently asked questions
You will need a candle, a plate, a jar, water, and possibly some food colouring.
The lit candle is placed in the centre of the plate and covered with an upside-down jar. As the candle burns, the air inside the jar heats up and expands, creating higher air pressure. When the candle goes out, the air inside the jar cools, causing the pressure to drop. As a result, water is drawn into the jar to equalise the pressure.
This experiment demonstrates the relationship between temperature and air pressure. It also shows how a vacuum can be created when pressure changes occur.
You can experiment with different jar sizes, water temperatures, or the number of candles used to observe how these variables impact the water level. Alternatively, you can try using a different heat source that does not involve chemical processes to isolate the physics contribution.
