Inside: Shark science is fascinating. Not that long ago, scientists discovered that sharks have build-in barometers. They detect the drop in air pressure (and water pressure) and move to safety during violent weather. Today, we will make a homemade barometer and learn how sharks detect the approaching hurricane.
If you’ve been searching for a perfect shark activity to do in anticipation of shark week, look no further. Not only is this science activity hands-on and fun but you also will also learn a lot about how sharks predict the weather by using mechanoreceptors within the inner ear (aka built-in barometers). Then we’ll make our own barometers with simple household items.
What’s atmospheric pressure?
Three hundred and seventy-five years ago, an Italian physicist, Evangelista Torricelli, experimented with mercury and noticed that mercury moved up and down inside a glass tube from day to day. He realized that it was caused by changes in atmospheric pressure.
The atmosphere is the layer of air around the Earth. We live at the bottom of the atmosphere. The atmosphere is full of air.
That air has weight, and it presses down on the planet Earth (and us). Pressure varies from day to day and decreases with increasing altitude (higher elevation, less air → less pressure). Scientists call this pressure atmospheric pressure, or simply air pressure.
Low atmospheric pressure is associated with high winds, snow, rain, and storms. On the other hand, high atmospheric pressure usually means clear skies and cool, dry air.
Shark Science: What do sharks do during a hurricane?
In 2001, scientists looked at the data from tagged sharks after the storm Gabrielle hit Florida and discovered that the blacktip sharks left the area en masse seven hours before the storm hit!! Once the storm passed, the sharks returned to the area.
The same phenomenon was observed multiple times and with different kinds of sharks. It’s now believed that sharks sense pressure by using hair cells in their vestibular system. When sharks detect violent weather approaching, their instinctive reaction is to move to safety. Deepwater has more mass to absorb energy, and it remains calm even during a hurricane. So sharks can wait out the bad weather in relative safety.
How to Make a Barometer
Ever since Evangelista Torricelli built the first barometer in 1643, people have used it to predict the weather. Today, there are two types of barometers: a mercury barometer (just like the one Torricelli built) and an aneroid barometer (non-liquid barometer).
You can easily make an aneroid barometer at home. All you need are simple materials you probably already have in your house. Hands-on activities are wonderful tools for discovery and learning.
Find out below how to make a homemade barometer and how it works.
Homemade Barometer in Five Minutes
What you need
- A jar or tin can
- A large round balloon
- A rubber band or two
- A small stirring stick or drinking straw
- Pen and paper (graph paper is even better)
What to do
- Use the scissors to cut the neck off of a balloon.
- We usually use a simple mason jar, but today as I got ready to photograph this experiment for you I realized that all our jars are in use, so I ended up with a pretty milk jug. Stretch the cut balloon tightly over the mouth of the jar and seal it with the rubber band. It should look like a drum and sound like a drum when you tap it lightly. Note: The air inside the jar will stay at a fairly constant pressure because air particles can neither enter nor escape through the balloon covering the mouth of the jar.
- If your straw has a bent end, cut that off. We want a more precise pointer. You can either flatten one end of the straw with your fingers (about 1 inch) and use the scissors to clip it to a sharp point. Or you can do what we did and cut a small arrow from paper and insert it inside the straw. Note: You can color the pointer with a marker to make it more noticeable (and festive).
- Glue the straw on top of the jar. Put a small amount of glue in the middle of the balloon and press in the unflattened end of the straw. The pointed end of the straw should stick out. Note: super glue worked best for us. Craft glue wasn’t great, but it can work if you remain patient and don’t move until the glue dries. A glue stick didn’t work at all.
- Tape a piece of paper to a wall. Place the jar so it aims at the paper. The pointer should be close to the paper, but not actually touching it. Note: My kids like to have a shark image to look at during this experiment, so we alternate between shark posters, shark books, and shark images I found on the internet.
- Record changes in the pointer’s position. When the pressure rises, the pointer will aim higher up. When the pressure falls, the pointer will point lower down. Mark the position of the pointer when you notice that it changed position. Note: you can number each new position in order “1,” “2”, “3,” etc.
The Science Behind Barometer
When air pressure rises, the air outside of the jar is heavier than the air inside of the jar. It causes the balloon to be sucked down into the jar, pushing the opposite end of the straw higher on the graph. High pressure = mild, fair weather
When air pressure outside of the jar is lower than inside the jar, the air inside the jar presses against the balloon. It causes the balloon to stretch out, causing the pointer to be lower on the graph. Low pressure = greater chance of rain, snow, clouds, etc.
Why? It’s a subject of another post, but if you can’t wait to find out, Weather Works Inc. has an answer.
Here is a fun variation for you to try: build two barometers and put one outside in the direct sunlight. Compare the data and determine if the direct sunlight caused an inaccurate reading of atmospheric air pressure.
You will notice that the barometer reading changes in response to temperature as well as direct changes in pressure. The air trapped inside the jar will get warmer than the air outside of the jar (especially on a hot summer day). The warm molecules try to take up more space than they have, creating a greater pressure pushing out of the container.
Are you interested in more temperature experiments? Place your barometer in a pan of hot water and observe what happens.
The most fun part: have your kids explain in their own words to grandma or a neighbor how they made a barometer and how it works.