Have you ever been doing chores and wondered how your vacuum cleaner sucks up all the dirt? Or have you ever been curious why astronauts wear such complex suits in space? In this experiment, we will answer both of these questions and learn about pressure to create our very own vacuum!
Materials
Clear glass cup with water
Bowl or shallow plate
Small candle
Lighter
Time Estimated:
10 minutes
Directions:
First, fill the cup about halfway with water, or with just enough that you will be able to cover the bottom of the bowl.
Pour the water into the bowl, and if there's any extra, pour it down the sink. We are going to use the empty cup!
Next, place the candle in the bowl and have an adult help light it.
Carefully cover the candle with the cup, making sure not to bump into it so it doesn’t go out.
Now, watch what happens to the water level inside the cup as the flame burns out!
Think Like a Scientist!
Why does the flame go out?
When it goes out, why does the water level inside the cup rise?
How Does it Work?
In this experiment, we explored pressure, specifically what happens when it changes. When we covered the burning candle, we trapped all the heat inside. The trapped air molecules move faster as the temperature increases, and this increases the pressure inside the cup. Eventually, the pressure gets so high that it forces most of the air out through the bottom. This makes the flame go out because fire needs the oxygen in air to burn! The temperature again changes inside our glass, this time very quickly. The remaining air cools off and creates another pressure difference. However, now the air inside has a lower pressure than its surroundings, and it “pulls” in water until the pressure inside matches the pressure outside. This creates what scientists call a partial vacuum, or a space with very low pressure compared to the atmosphere. Fluids and gasses move from high pressure areas to low pressure areas, so the pressure difference creates a vacuum by pulling things inside until it’s balanced. Can you think of ways to increase the strength of our vacuum? What if we added more candles to create more heat?
Further Exploration:
All types of scientists study pressure, and many create vacuums such as the one we made to perform tests in more ideal conditions. For example, an engineer designing an astronaut’s suit will test it in a partial vacuum to make sure it can withstand space, which is one of the strongest vacuums to exist! They want to make sure nothing from inside the suit gets pushed outwards due to the giant pressure difference, and this is of course necessary for the astronaut’s safety. Interestingly, all vacuums are partial vacuums, even the vacuum of space! A full (or perfect) vacuum is a region containing absolutely no matter, and even “empty” space has a few particles spread throughout.
Anticipated Concerns:
Be sure to ask an adult for help with lighting the candle.
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