The world is turning around and around… all the time! And this has a big influence on where ocean currents go and how winds blow (It doesn’t, however, influence the vortex that appears when you drain your bath tub!). We call this the «Coriolis effect» or «Coriolis force».
For the experiment, you’ll need:
- a cutting board
- a long ruler
- glue or tape (to glue the ruler to the cutting board)
- a pencil
- a couple of pens
- a white paper
- a second pair of hands (someone to help you with the experiment)
Cut out a large* circle from he paper and pin it to the middle of the cutting board with the pencil (check with your parents first that they are ok with that!). Glue or tape the ruler onto the cutting board such that it goes over the paper circle.
Now draw a line along the ruler’s edge while your helper turns the paper circle clockwise. What do you see?
The paper circle represents the world as seen from the South Pole. What would the same thing look like from the North Pole? Turn the paper circle the outer way round to find out!
*but the diameter needs to be smaller than the length of the ruler!
- a bowl
- a thermometer
- ice cubes
- some water
- something to stir with
Add water and ice cubes to the bowl and then add the thermometer. Stir a bit. What does the thermometer show?
Now add a little salt and stir well to solve the salt in the ice water. What happens to the temperature? What happens if you add even more salt? How cold can you get your water?
When a mixture of water and ice is in equilibrium, the temperature is at freezing point. When you add more salt, that lowers the freezing temperature (the more salt, the lower the freezing point) and the mixture is no longer in equilibrium.
Heat from the water is used to melt, and the temperature of the mixture sinks, either until all ice as melted, or until the temperature of the water is the freezing temperature.
Everybody knows that once upon a time, Archimedes sat in his bath tub and all of a sudden shouted «Eureka!». But do you know why he did that?
For this experiment you’ll need:
- A large glass / jar / jug (which has to be see-through)
- A small plastic mug (which fits inside your glass / jar / jug)
- A couple of coins, small pebbles or something else «heavy»
- An apple (or something else that floats)
- A non-permanent pen
Fill the large glass with water and mark the water level on the outside of the glass. Then put the little plastic mug inside. Fill as many coins (or other «heavy» things) into the small plastic mug until it sinks. As you are filling coins into the small plastic mug, the water lever rises. Mark how high the water level is right when there are so many coins inside the plastic mug that it sinks!
Now take all the stuff out of the large glass again. The water level goes back to where it was before.
What do you think would happen if we added all the coins to the large glass directly, without putting them inside the floating plastic cup? Do you think the water level would change? And if it changed, where would it end up relative to the two marks you already made on the glass?
Now try and check whether you guessed correctly!
Then do the experiment again, this time with the apple. What happens?
You have probably seen the picture of people floating on their backs in the Dead Sea, reading a newspaper or a book. But do you know why they are floating?
- 2 large plastic containers
- Water and a lot of salt
- Different kinds of vegetables and fruits (or other things you might want to experiment with)
Mix a lot of salt with the water (salt dissolves more easily if the water is warm!) in one of the plastic containers to represent the Dead Sea, and fill the second container with tub water at the same temperature as your «Dead Sea». In the Dead Sea, the salinity is 33,7%, that means to reproduce that you need ca 1 kg salt for 4 liters of water!
Now look at all your fruits and vegetables. Which, do you think, will float in the «Dead Sea»? Which will sink? Does your answer change if you look at your second container with tub water?
Does the coconut float? Fra Forskningsdagene i Bergen. Foto: UNI research
With all the colourful liquids you can find in your kitchen, only your imagination is limiting what you can play with in this experiment!
Start with the least dense liquid and carefully add the others with increasing density.
Here are a couple of examples of liquids you might have at home:
Baby oil – 0.83 kg/L
Rapeseed oil – 0.92 kg/L
Ice cubes – 0.92 kg/L
Milk – 1.03 kg/L
Dish soap – 1.06 kg/L
Black currant juice – 1.33 kg/L
Honey – 1.40 kg/L
Baby oil, milk, dish soap, black currant juice and honey… might not taste very nice, but certainly looks awesome! Foto: P. Langebroek
Warm water needs more space than cold water — check it out in this experiment!
You will need:
- 1 small plastic bottle
- 1 drinking straw
- modelling clay / play dough
- Food dye (not strictly necessary, but more fun)
- A large, high container in which the small plastic bottle can stand
- cold and warm water
Fill the bottle with cold water (and add a couple of food dye if you like). The bottle should be completely full, so full that it is almost overflowing.
Place the straw in the bottle and lock the bottle with modelling clay. At least 10 cm of the straw should be left above the lock! Test that the lock is water tight by slightly pressing on the bottle. Water should now be rising in the straw, but not spilling out of the lock! It is not easy to get the lock completely watertight, you might need several attempts.
Now place the bottle in the larger container and fill the container with hot water (careful – don’t hurt yourself!). Wait a couple of minutes and observe what is happening. How high is the water rising in the straw?
Now put really cold water in the larger container instead of the hot water. What happens?
Try this for different water temperatures – lukewarm, really hot, medium hot, cold, etc. What happens now?
Researchers have found out that the water in the deep ocean is slowly warming. What do you think the consequences will be?
You will need some sea water.
Can you think of a way to measure the salinity of the sea water? There are many possibilities to figure out how much salt there is in sea water! How would you go do it?
When you fetch your sea water, take a little more than you need and put it in a bowl or glass somewhere where it can sit without being disturbed (maybe on top of a cupboard?). As water evaporates, what happens? Check occasionally on your glass with sea water, and look at how much water vanished since you last checked. What is happening in the glass? At what point can you notice salt crystals forming? How long does it take until all the water is gone?
You will need:
- Two glasses (or plastic cups)
- Food dye
- Access to a freezer
- Ice cube tray
Mix the food dye and water, put it the ice cube tray, put the ice cube tray in the freezer and wait… Now you have colored ice cubes!
Fill the two glasses with tap water. Take one of the glasses and mix in salt until the water tastes like sea water. Then, put one ice cube in each of the glasses and watch what happens. Where does the ice melt fastest? And why?
For advanced oceanographers: you can also use «clear» (not dyed) ice cubes, then seeing what happens is a little more difficult (and a little more exciting :-))
You can read about what happens – and why – on my friend’s and former colleague Mirjam’s blog «Adventures in oceanography and teaching«. There you can find many more exciting experiments, too!