Make Things Sink, Then Float

You will need

  • Modelling clay or blue tag
  • Marbles (if you don’t have marbles, use small rocks)
  • Water
  • Glass bowl or a large glass jar

What to do

  1. Fill the glass bowl or jar with water.
  2. Drop the marbles into the water. They quickly sink to the bottom. Roll the clay into a ball and drop it into the water as well.
  3. The clay also sinks like the marbles.
  4. Remove the marbles and the clay ball from the water.
  5. Flatten the clay as much as possible, then shape it to make a boat and place it into the water. Now it floats!
  6. Add one marble as a cargo. The boat settles lower, but still floats.
  7. Add more marbles, one at a time. How many can you add before your boat sinks?

Background

Large ships float on water, even though they are very heavy.  However, a small object like a marble sinks. The mass of the object does not matter. Whether or not an object floats depends on its density and how much water it “displaces”, or pushes aside.

When the clay is shaped like a ball, it does not displace much water and it sinks. When shaped like a boat, the clay has a bigger area and displaces more water which makes it float. When adding your cargo of marbles, the boat settles lower to displace more water and carry the extra mass. When adding too many marbles, the boat will settle below the water line and sink.

This is important for ships. Too much cargo can lower them too close to the water line and make them vulnerable to sinking.

You can watch this experiment as a video here:

Test the Flow of Liquids

You will need

  • 3 Glass jars (empty and cleaned)
  • 3 Marbles (cleaned and dried)
  • If you don’t have marbles, use small rocks instead.
  • Water
  • Vegetable oil, for example olive oil or sunflower oil
  • Syrup or honey
  • Cooking oil and syrup or honey can still be used or eaten after this experiment.

What to do

  1. Fill each glass jar with a different liquid at least half full. Make sure that the liquids have the same height in each jar.
  2. Drop a marble into each one and observe how fast the marble falls through the liquid inside.
  3. The slower the marble falls, the higher is the viscosity of the liquid. Which liquid in this experiment has the highest and which the lowest viscosity?

Background

It takes much longer to pour syrup into a glass than to pour water. This is because syrup has a high “viscosity”. This means that it does not flow easily. The higher the viscosity of a liquid, the slower it will flow.

You can test the viscosity of a liquid by dropping a marble into it. The slower the marble falls, the higher is the viscosity of the liquid.

You can watch this experiment as a video here:

Red Cabbage Indicator

You will need

  • 1 Sauce pan
  • 1 Chopping board
  • 1 Knife
  • 1 large glass jar
  • 4 small glass jars
  • 1 Red Cabbage
  • Vinegar, lemon juice, water and bicarbonate of soda to test

What to do

  1. Carefully chop the red cabbage leaves into small pieces on the chopping board.
  2. Put the red cabbage in a sauce pan and add water until the red cabbage leaves are completely covered.
  3. Gently boil the red cabbage for 10 to 15 minutes.
  4. After the sauce pan has cooled down, collect the water in a large jar.
  5. To better see the red cabbage water’s colour add some water to dilute it.
  6. Transfer the red cabbage water into the 4 small jars.
  7. Add a dash of vinegar to the first small jar with red cabbage juice and observe what happens.
  8. Repeat step 7 for the other substances you want to test. Each substance goes into a new small jar with red cabbage juice.
  9. What colour changes do you observe?

Background

Red cabbage juice is a pH indicator. This means it changes colour depending on if it is in an acidic, alkaline or neutral environment. In this experiment you are testing some acids (vinegar and lemon juice), some alkalis (bicarbonate of soda) and a neutral substance (water).

Which colour changes can you observe in your experiment? What colour does red cabbage indicator have in acids, bases or with neutral substances?

You can watch this experiment as a video here:

Measure the Wind

You will need:

  • Scissors
  • Glue stick
  • Thin cardboard
  • Short pencil with rubber
  • Drinking straw
  • Small plastic pot, e.g. from yoghurt
  • Pin or needle
  • Blue tag or modelling clay
  • Compass, you can just use a Compass App on your mobile phone

What to do:

  1. Make a hole in the middle of the bottom of the plastic pot using the pencil. Then push the pointy end of the pencil through the hole.
  2. Carefully cut four small triangles from the cardboard using the scissors.
  3. Glue each of the 4 small triangles to the yogurt pot. Look at the image to see where they should go. These will show the direction of the wind.
  4. Cut two larger triangles from the cardboard using the scissors.
  5. Cut a short slit at either end of the straw. Insert the two large triangles into the slits to make and arrow-shaped pointer. This is called a “vane”.
  6. Carefully push the pin or needle through the middle of the drinking straw. Then push it into the rubber on the pencil end.
  7. Make a ring from blue tag or modelling clay and push the pot firmly into it, so it cannot blow away. Your wind vane is ready to use.
  8. Place your wind vane outside. Position it so that the small triangles point North, East, West and South. Use a compass to help you. The vane swings around in the direction of the wind.

You can watch this experiment as a video here:

Architecture with Fruit Pastilles

You will need:

  • 2 Plates
  • Toothpicks
  • 1 Bag of Rowntree’s Fruit Pastilles or other gummy sweets

What to do:

  1. Place 4 fruit pastilles in a square on a clean plate and connect them with toothpicks.
  2. Place 1 toothpick in each fruit pastille, so that they stick straight up.
  3. Attach 4 more fruit pastilles to the top of each toothpick and connect them with 4 more toothpicks. You now have a fruit pastilles cube.
  4. On the second plate, place 5 fruit pastilles to form a pentagon and connect them with toothpicks.
  5. Now press 2 toothpicks into 2 neighbouring fruit pastilles, so that they come together at the top to form a triangle. Press 1 fruit pastille firmly onto both toothpick tops to finish the triangle.
  6. Repeat until you have 5 new fruit pastilles suspended over 5 toothpick triangles.
  7. Use 5 more toothpicks to connect the 5 new fruit pastilles in a new pentagon.
  8. Leave both designs overnight to set.
  9. The next day test the strength of your designs by placing books on top. Which structure can bear more weight?

Background

Architects and engineers have to think about how the parts of a building will carry stress. The weight of heavy buildings pulls on the beams holding up the buildings.

From your experiment, do you think that squares or triangles will be best for distributing stress so that a building can stay standing over a long time.

You can watch this experiment as a video here:

Modelling Fossil Formation

You will need:

  • Brown sugar (about 500 g)
  • Dinosaur toy figures or other animal to figures (plastic or wood, washed and dried)
  • 1 White chocolate bar (cooking chocolate works best)
  • Microwave
  • 2 Table spoons
  • Baking pan
  • Heat proof bowl, e.g. glass or ceramic
  • Brush (not necessary, but helpful)

What to do:

  1. Pour the brown sugar into the baking pan. Use the back of the spoon to pat it down.
  2. Arrange your dinosaur or animal toys over the brown sugar. Gently press each toy down to make a dent in the brown sugar. Then remove the toys.
  3. Break the white chocolate bar into small pieces and place them in the heat proof bowl.
  4. Microwave the chocolate in the bowl for 30 seconds and then stir. Continue microwaving for 20 seconds at a time stirring after each time until the white chocolate is completely molten.
  5. Slowly pour the molten white chocolate into the dents in the brown sugar. Then place in the fridge for 1 hour.
  6. When the white chocolate has hardened, carefully dig each fossil out of the brown sugar with a spoon.
  7. Carefully clean most of the brown sugar off using water and your fingers. If you have a brush you can use it to remove the sugar. Your fossils are edible.

Background

Fossils are remains of organisms that lived a long time ago. This experiment is a model for fossil formation. The brown sugar represents soft soil or sediment where we can often find the imprints of creatures, for example foot prints.

The molten hot chocolate represents hot lava which fills empty spaces left by dead, buried organisms. The lava cools and finally forms rock fossils, showing us an image of the dead creature.

You can watch a video of this experiment here:

Friction with Rice

You will need

  • 1 Plastic bottle (500 ml)
  • Rice (you can still eat it after the experiment)
  • 1 Funnel
  • 1 Chop stick or pencil

What to do

  1. Fill the plastic bottle to the rim with rice. You can use the funnel to help you.
  2. Pick up the bottle and hit its bottom against the table several times. This will compact the rice more and let air escape.
  3. There is some more room in the bottle now. Add more rice until it reaches the rim of the bottle.
  4. Now insert the chop stick or pencil into the rice. Push it down as far as you can.
  5. Take a hold of the chop stick or pencil and lift it up. What happens?

Background

There are different forces acting on the bottle. The force of weight or gravity pulls it down to Earth. When you insert the chop stick or pencil into the rice, there is an additional force of friction between the rice and the chop stick/pencil. The force of friction acts in the opposite direction of gravity.

If the forces of gravity and friction are equal, you are able to pick up the bottle when only holding on to the chop stick/pencil. If forces are equal and act in opposite directions, we say that they are balanced. In this experiment the forces of friction and of gravity are balanced.

You can watch a video of this experiment here:

Candle Experiment

You will need

  • Candle
  • Matches or lighter
  • 3 Jars of different sizes
  • Heatproof base, for example a ceramic plate
  • Stopwatch/timer (your mobile phone will do)

What to do

  1. Put the candle on the heatproof base and light it.
  2. Put the smallest jar upside down over the candle and start the timer.
  3. Time how long it takes for the candle to go out and record the time.
  4. Repeat steps 2 and 3 for the medium sized jar and the large jar.
  5. Record for each candle how long it burns. Under which jar does the candle burn longest?

Background

Oxygen is needed for a fire to burn. This is also true for candles. The oxygen is normally supplied by the air.

When placing a jar over the candle, the amount of oxygen for the candle is limited. The candle goes out when all oxygen in the jar is used up. The amount of oxygen depends on the size of the jar.

Under which jar does the candle burn longest? Why do you think that is?

You can watch a video of this experiment here:

Build a Compass

You will need

  • Fridge magnet
  • Small bowl
  • Water
  • Needle
  • Piece of cork

What to do

  1. Rub the fridge magnet along the needle several times. You always need to move the magnet in the same direction along the needle. This is done to magnetize the needle and turn it into a temporary magnet.
  2. Gently push the needle through the middle of the cork. Be very careful not to sting yourself.
  3. Fill the bowl with water.
  4. Place needle and cork in the water.
  5. If left alone the needle will align in a North-South direction in the water. Just like a compass needle would.
  6. If you wish you can use the fridge magnet to manipulate the needle and move it in the water.

Background

Rubbing the fridge magnet along the needle magnetizes it and turns it into a temporary magnet. Temporary magnets only remain magnetic for a short amount of time. Permanent magnets like the fridge magnet are always magnetic.

When inserted into the cork and floating in water the needle acts like a compass. Earth has a magnetic field where the poles are located at the North and the South pole. Therefore, the needle will move to align in a North-South direction when floating in water.

You can watch this experiment as a video here:

Grow a Crystal

You will need

  • Short length of wool or string
  • Warm water
  • 2 Paperclips
  • 1 Plate
  • 1 Spoon
  • 2 Glass jars
  • Washing soda

What to do

  1. Fill both jars with warm water. (From the tap is fine.)
  2. Add washing soda to both jars and stir until no more washing soda dissolves.
  3. Attach a paperclip to each end of the string or wool.
  4. Place the ends of the string in the jars, so the string hangs between the jars.
  5. Place a plate between the jars to catch the drips of the solution flowing along the string or wool.
  6. Leave the jars for one to two weeks in a safe place and observe what happens.

Background

The washing soda solution slowly soaks the string or wool and flows along it. As the solution drips off some washing soda is deposited slowly forming a crystal.

Water flowing underground dissolves minerals when it seeps through rocks. The minerals are deposited when the water drips of a cave roof. A crystal is formed that hangs off the cave rood which we call “stalactite”. When the water drips to the floor it deposits minerals there forming a crystal growing up from the ground which we call “stalagmite”.

In your experiment a stalactite grows hanging from the string or wool.

You can watch a video of this experiment: