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You may have heard about the large container ship that got stuck in the Suez Canal in Egypt for several days in 2021. The canal is about 190 kilometers long and is one of the busiest waterways in the world. Around 50 container ships pass through it every day.

Containers usually carry goods from Asia to Europe. All shipping containers in the world are exactly the same width: 2.44 meters and they are all the same height: 2.59 meters. Their lengths can vary, though. Sometimes the ships look like apartment buildings stacked with containers, some are as much as 70 meters high and almost 400 meters long. These ships can carry around 11,000 containers. Ships are getting bigger and bigger, but there is a limit. If they become too large, they won’t be able to pass through the Suez Canal.

How does such a huge container ship stay afloat?

You might wonder why such a large ship doesn’t tip over or sink. The shape of the ship, the air inside it, and the way it is loaded all play an important role.

Boats come in all shapes and sizes. There are small rowboats as well as large sea ships and they all float on water. Nails however, sink when you put them in water. Yet boats like nails, are made of iron and boats are heavy while nails are light. So why does a boat float while a nail sinks?

Have you ever noticed that you seem lighter when you’re in a swimming pool? That’s because the water pushes back on you and supports part of your weight.

Experiment 1: How can a large, heavy ship stay afloat?

That’s because of the air inside the ship. Try this yourself: a clean, empty jam jar with its lid on will float in water. Push the jar completely underwater, do you have to push hard? What happens when you let go? It still floats. But if you take the lid off, it tips over and sinks. Large steel ships work in exactly the same way. As long as they are filled with air and not water, they will float. The water under the ship pushes it up just as hard as gravity pulls it down. As long as these two forces are balanced, the ship stays afloat and can keep sailing!

Experiment 2: The shape of the ship is also important.

Try this: Take some marbles and a small lump of clay. Put the marbles in a container of water, they sink immediately. The clay doesn’t do much better. Now flatten the clay into a pancake shape. What do you think will happen? The clay sinks more slowly, but it still doesn’t float. This has to do with the shape of the clay. It’s not just the weight that matters, the shape is important too. Now try shaping the clay into a little boat. Did it work? Yes, it floats!

Experiment 3: How heavy and how big

Whether something sinks or floats depends on both its weight and its size. Try this: place a small ball of wax in water. Now see how many marbles (containers) you can load into the wax ball without it sinking or tipping over. How many marbles can your “boat” hold before it sinks? Try the same with larger or smaller objects that float on their own and can hold marbles. In other words, make bigger and smaller boats. At what size or with how many marbles does it stop floating?

When you put something in water, it pushes the water aside. The water pushes back with the same force, this is called buoyancy. Whether an object sinks or floats depends on its weight. If the downward pressure is greater than the upward force, the object sinks. But sinking also depends on size. A larger object pushes more water aside, which increases the upward force. That’s why a large ship can stay afloat, even when it is heavily loaded.

Experiment 4: The “Cork Container” Ship

Want to try a fun experiment? Download the instructions and experiment with corks. Have fun!

 

You will need:

  • White paper
  • Pencil
  • Colored pencils or markers
  • Scissor 
  • Ta[e
  • Cocktail sticks
  • Piercing tool
  • 3 corks
  • Paperclips
  • Nuts
  • A tub or basin of water