Tag Archives: density

#TryThisTuesday: Rice Bottle

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Our #TryThisTuesday this week, is a challenge for you. The task is to fill a dry bottle with rice and lift it up using only a pencil.

Have a go or challenge your friends, once you think you’ve cracked it (or given up) scroll down to see how we did it!

The Solution

Take the lid off the bottle and push the pencil half way into the rice. Take the pencil out again and push it back in, repeat this about 10 times. Eventually, when you pull the pencil to take it out, the bottle will lift up with it!

This occurs due to the force of friction acting on the pencil and holding it in place. When you first pour the rice into the bottle, it will arrange itself with lots of gaps but every time you insert the pencil you push the rice down making it more compact or dense. Some grains may even break or change shape under impact with your pencil. The more you do this, the greater the surface area of rice that comes into contact with the pencil. This gives a greater force of friction. Friction is a force of resistance between two objects when they  move past each other. The force is so strong at this point that it doesn’t allow the pencil to slip past the rice and so the rice (and the bottle) moves with the pencil as you lift it.

In the Real World…

This works in a similar way to quicksand. If you were to step onto quicksand, you would compact the particles, making them move closer together and lock around your foot, pulling you in. The friction makes it difficult for you to pull your foot out. Don’t worry too much though – quicksand is much denser than a human being so you wouldn’t be able to completely sink in it. As we learnt from our ketchup packet submarine and the oil and water experiment – less dense substances float above denser substances so you would stay above the surface of quicksand!

#TryThisTuesday: Oil and Water

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For this experiment all you will need is a clear bottle or jar with a lid, water, cooking oil and some washing up liquid.

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Fill the water bottle half full with water.

Pour about 100ml of oil in to the bottle and observe what happens.

The oil should float on the water. Try and mix them together or challenge other people to mix them! It is impossible, the oil and water always separate out again.

Add a squeeze of washing up liquid to the bottle and shake. The oil and water now mix together.

The Science

Oil is less dense than water so floats on top. Oil and water don’t mix together as the water molecules are more attracted to each other than the oil molecules. Oil molecules are hydrophobic or ‘water-fearing’.

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Washing up liquid molecules are attracted to both water and oil. When you add a squirt in, one end of the washing up liquid molecule attaches to a water molecule and the other end attaches to an oil molecule. This creates a mix of water with oil droplets spread throughout it. This is because one end of the washing up liquid molecule is hydrophobic (water fearing) and one is hydrophilic (water loving).

The washing up liquid acts as a stabiliser and creates an emulsion. This is a mixture of two liquids that wouldn’t normally mix.

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Real Life Applications

We use washing up liquid when we are washing up as it attaches to the oil on the dirty dishes and lifts it off into the water.

Animals that live in the ocean also stay warm by producing an oily substance on their fur or feathers which keeps the cold water away from their skin.

#TryThisTuesday Mini Fire Extinguisher

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You will need: large tall glass, bicarbonate of soda (baking soda), vinegar, a candle and some matches

image11. Add 4 teaspoons of bicarbonate of soda to the glass

2. Pour in roughly 150ml of vinegar, the mixture will fizz.

3. Light the candle.

4. Once the mixture has stopped fizzing, pick up the glass. Without pouring out the vinegar, gently tip the glass from a few centimeters above the candle. Imagine that there is an invisible liquid inside above the mixture. The candle will go out!

The Science

You have produced a gas, carbon dioxide, by mixing the bicarbonate of soda with vinegar (also known as acetic acid). Bicarbonate of soda contains carbon dioxide, but it is attached to other molecules. When you mix it with vinegar the bicarbonate breaks down and releases carbon dioxide as a gas.

The following reaction takes place:

bicarbonate of soda + vinegar → sodium acetate + water + carbon dioxide

NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2

Carbon dioxide is heavier than air so stays in the glass until you tip it over the candle. When you pour carbon dioxide on a candle it stops the flow of oxygen which is needed for a flame to burn, and the candle is extinguished.

Real fire extinguishers also use carbon dioxide to put out fires, it is compressed (squashed) into cylinders and sprayed at fires.

#TryThisTuesday: Submarine

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This week’s experiment will show you how a submarine works using just a water bottle and a ketchup sachet.

  1. Take a large (2 litre) plastic bottle and fill it with water
  2. Test a few ketchup sachets in a bowl of water to see if they float, not all of them will have an air pocket in.
  3. Add an unopened sachet of ketchup to the bottle. The sachet should float, but if it doesn’t, try adding some salt to the water. Salt increases the density of water, making the sachet float better.
  4. Make sure the bottle is full of water to the top.
  5. Screw on the top very tightly and squeeze the bottle hard.

The sauce submarine will sink to the bottom. If you let go it will float back up.

You can challenge other people to get the sachet to the bottom, lots of people will try and shake it or turn it upside down!

The Science

This experiment is all to do with how things float, or the buoyancy of an object. Water pushes up on the ketchup packet with the force equal to the weight of the water that the ketchup packet pushes out the way.  If the displaced water is heavier than the sachet, then it will float because it is less dense than the water.

When you squeeze the bottle you apply pressure to the liquid inside. Liquids cant be compressed (squashed) so the pressure is transmitted to the sachet. The ketchup sachet has some nitrogen gas in (to keep it fresh). The gas is compressed and the sachet sinks and therefore displaces less water and sinks. As soon as you let go the sachet expands again and floats.

Submarines use similar systems to allow them to sink and float easily.

 

#TryThisTuesday: Lava Lamp

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This week’s experiment will show you how to create the 1960’s invention – the lava lamp – at home!

You can create your lava lamp in a beaker, a glass or a plastic bottle, whatever you have lying around that you can see through.

  1. Start by filling your container 1/4 full with water and add some food colouring of your choice.20161108_160122
  2. Add oil until its nearly full to the top. Wait a minute or two and the oil should separate out and sit above the water.20161108_160212
  3. Drop in a Alka-Seltzer or any other effervescent (fizzy) tablet and watch the bubbles rise.

The Science

Oil floats on top of water because it is less dense and water molecules stick closely together due to their hydrogen bonds, making it difficult for the oil to mix in.

The tablet is more dense than the oil and the water so sinks directly to the bottom. There it reacts with the water to produce the gas, carbon dioxide (CO2). CO2 is less dense than both the water and oil so it rises to the top, carrying some water molecules with it, these are the bubbles that you can see. The bits dropping back down are the water molecules sinking again once the gas has escaped.

A real lava lamp uses wax that is heated by a bulb. The hot wax expands, becomes less dense than the water and so rises. When it cools, it shrinks, becomes denser and sinks.

World Egg Day: Eggsellent Experiments

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Happy world egg day! Here are some cracking eggsperiment that you can at home on this very important day:

Egg in a Bottle

For this experiment you will need a hard boiled egg, an empty plastic bottle, a scrap of paper and a lighter.

Light the paper and drop it into the bottle. After a second place the egg on top of the bottle and observe the results.

The lit paper heats up the air in the bottle, causing it to expand slightly and for some air to escape. The egg creates a seal so more air cannot enter. As the air cools inside the bottle it decreases the pressure and forces the egg into the bottle.

Floating Egg

All you need to try this one is an egg, a glass, water and salt.

Fill you glass half full with tap water and carefully place the egg inside. It should sink. Add some salt until the egg floats. The salt increases the density of the water, when you add enough the egg becomes less dense than the water so floats to the top.

Next dribble spoonfuls of tap water down the side of the glass until it is full. The egg should appear to float in the middle of the glass, it is actually floating on top of the salt water with a layer of fresh water above it.

Hard boiled Spin

Lay a hard boiled egg flat on its side and spin it. Put your finger on it to stop and then let go, nothing remarkably happens there. Try the same with a raw egg and when you let go it will start spinning again on its own accord.

This is all due to momentum. When you spin the eggs you spin their insides too. In the hard boiled egg, the insides are fixed to the shell so it behaves as you would expect. In the raw egg the insides continue to spin after you’ve stopped the shell. When you let go, the momentum of the spinning yolk carries the shell and the whole egg starts spinning again.