# #TryThisTuesday: Walking Water

#### Our Try This Tuesday series of experiments to try at home is back with a colourful water-based experiment from Street Scientist, Ailie.

You will need:

• Red, yellow and blue food colouring
• Kitchen roll
• 6 Clear cups, roughly the same size
1. Add water to three of the cups so they are 3/4 full. Then add 5 drops of red food colouring to one cup of water, blue into the second and yellow into the third.
2. Place the cups in a circle with the empty cups in-between the ones with water in (You may want to put some paper underneath the cups if you are worried about spills).

3. Take 6 sheets of kitchen roll and fold them twice to make a thick strip as below. You may want to cut them to be a bit shorter if you are using small cups, I cut off the bottom 1/5th.

4. Place one end of each strip of kitchen roll into one of the cups with water in and the other end into an empty cup next to it. Can you predict what colours might form in the empty cups?

5. Wait an hour then check back in to see if your experiment is working! Mine looked like this:

Eventually the empty cups will be as full as the cups feeding into them!

### Colour Theory

Did you notice something the 3 colours you started with had in common? They are the primary colours. Therefore, mixing them creates the 3 secondary colours – purple, green and orange.

This gives us a simplified version of a colour wheel. The colours opposite each other on the wheel, and in our cup circle, are ‘complimentary’ meaning they contrast one another i.e. purple and yellow.

If we were to add more empty glasses in between the colours we have here we would make tertiary colours!

### The Science

The water moves up the paper towel through a process called capillary action which is the ability of water to flow through narrow spaces, even against gravity! Capillary action works as molecules in liquid like to stick together (cohesion) and also like to stick to walls of a tube (adhesion). Together these forces act to propel the liquid through the tube or narrow space. The narrower the space, the quicker the water moves and the higher up it can go.

Plants rely on capillary action to move water all the way up from their roots to the leaves at the very top, where it is needed for photosynthesis (the production of glucose for energy). Just as humans have blood vessels to carry important substances around our body in the blood, plants have a tissue called xylem which is made up of millions of tiny tubes. Water moves up through the tiny cubes by capillary action, without wasting any of the plant’s energy.

One way to easily see capillary action working in the xylem is to cut the very bottom off the stem of celery or cabbage and put it into some water with food colouring. Given enough time, you will see the coloured water move to the top of the plant and stain the leaves. When a plant has been picked it is no longer undergoing photosynthesis and producing energy, therefore we have shown that the water is moving up to the top of the plant by a passive process.

Kitchen roll is designed to be very absorbent meaning it is able to hold lots of liquid – great for kitchen spills. To be able to do this, there are lots of little spaces in-between the fibres in kitchen roll which fill with water. Together they form the narrow spaces which the water uses to move up the tissue and into the adjacent empty cup. There, the colour mixes with the water from the cup on the other side to form our secondary colours.

# #TryThisTuesday: Bending Water

This week’s experiment is quick and simple but sure to amaze!

You will need:

• A balloon
• An indoor tap
• Clean dry hair

Method:

1. Turn the tap on so there is a very thin but constant stream of water flowing
2. Rub the balloon on your hair until you form static (about 10 seconds, until your hair begins to stand on end)
3. Slowly bring the balloon close to the flowing water while being careful not to actually touch the water
4. Watch the water bend towards the balloon!

### The Science

When you rub the balloon on your hair, tiny electrons are collected on the balloon. These electrons have a negative charge. This causes the balloon itself to have an overall negative charge, therefore it is attracted to things with a positive charge (opposites attract!). The flow of water has a positive charge, therefore the attraction is strong enough to pull the water towards the balloon.

This is known as static electricity!

# #TryThisTuesday: Rock Candy

This weeks Try This Tuesday takes a while, but you end up with a tasty treat!

You will need:

• A wooden skewer or chopstick
• Peg
• 1 cup of water
• 2-3 cups of sugar
• A narrow glass or jar

Clip the wooden skewer into the peg so that it hangs down inside the glass and is a couple of centimetres off the bottom.

Put the water into a pan and bring it to the boil. Pour about a quarter of a cup of the sugar into the boiling water and stir until it dissolves.

Keep adding more and more sugar, each time stirring it until it dissolves, until no more will dissolve. This might take quite a while!

When no more sugar will dissolve remove it from the heat and leave it to cool for about 20 minutes.

Pour the sugar solution into the glass or jar almost to the top. Then put your skewer back into the glass so it hangs down and doesn’t touch the sides.

Leave your glass in somewhere it won’t be disturbed. The sugar crystals will grow over 3-7 days. Once these have grown you can eat them!

### The Science

By mixing the sugar and water together when they were really hot, you have created a super saturated solution. This means that the water contains much more sugar than in could in normal circumstances. As the water cools back down the sugar leaves the solution (mixture) and becomes sugar crystals again, forming on the skewer.

Supersaturated solutions are used in real life. In a sealed fizzy drink the drink is saturated (full) with carbon dioxide, as the carbon dioxide is put in using pressure. When you open the drink, the pressure of the carbon dioxide is decreased, which causes your drink to be supersaturated as there is much more carbon dioxide dissolved than there would be at normal pressure. The excess carbon dioxide is given off as bubbles.

# #TryThisTuesday: Exploding Lunch Bag

Today we are going to make an explosive lunch!

You will need

• One small (sandwich size) zip-lock plastic bag
• Bicarbonate of soda
• Warm water
• Vinegar
• A tissue

Do this experiment outside, or at least in the kitchen sink. Put about a quarter of a cup of warm water in the bag with half a cup of vinegar.

Put three teaspoons of the bicarbonate of soda into the middle of the tissue and fold it up into a little parcel.

Partially zip the bag closed but leave a little space to add the bicarbonate of soda parcel in. Put the tissue parcel in the bag and quickly zip the bag completely closed.

Put the bag on the ground and step back. The bag will start to expand and hopefully pop!

### The Science

The bicarbonate of soda and the vinegar eventually mix together, the tissue just gives you enough time to get the bag shut. A reaction takes place between the alkaline bicarbonate of soda and the acidic vinegar, this is know as an acid-base reaction. The reaction produces carbon dioxide, which begins to fill the bag. After a while the bag can no longer hold any more gas so it pops!

The reactions between acids and alkalis are used lots in real life too. Farmers can treat acidic soil with alkaline lime fertilisers to neutralise the soil and allow plants to grow. It’s also a good way to treat a wasp sting; wasp stings are alkaline so you can treat them by putting vinegar on the sting.

# #TryThisTuesday: Milky Fireworks

For this week’s experiment you will need to raid your fridge and kitchen cupboards to get some milk, food colouring and washing up liquid.

Pour some milk into a dish or bowl, this works better with full fat milk (we’ll tell you why later!). Add small drops of your food colouring wherever you like in the milk.

Get some washing up liquid on the end of a spoon or cotton bud and gently tap the spots of food colouring with it.

The food colouring should burst out into colourful stars and wavy shapes. This happens because the washing up liquid molecules have a hydrophobic tail, these means that they don’t like water so try to get away from it by seeking fat molecules. The milk (especially if it is full fat milk) contains lots of fat molecules. So the washing up liquid moves around in the milk seeking out this fat and takes the food colouring along with it, creating these funky patterns.

This is why we use washing up liquid to clean our dishes. The hydrophobic, fat-loving parts cling to grease and fat. The head of the washing up molecules are hydrophilic, meaning they love water. The heads cling to the water and the tails cling to the grease, this pulls the grease and dirt from your plates and washes them away with the water, giving you sparkly clean dishes.

# #TryThisTuesday: Curly Fries!

Today we are looking at the science behind curly potato fries. First, let’s talk about how we make them.

1. Carefully chop up a potato into straight thick chips.
2. Boil around 250ml of water and stir salt into this water until no more salt will dissolve.
3. Fill a bowl with tap water and place half of your chips into this bowl.
4. When the salty water has cooled pour it into another bowl and add the rest of your chips to this.
5. Leave both bowls of chips out overnight.
6. The next day you should have one bowl of chips that are still hard and straight and the other bowl (with salty water in) will be full of chips that are more flexible, that you can shape into curls.

### The Science

The addition of salt to the water allows you to make curly fries due to osmosis. Osmosis is the movement of water from an area that has few molecules in the water to an area that has more molecules in it to try to even things out and create a balance.

Plants like our potato here are made up of millions of cells that have a cell membrane around its edge which allows some things in and not others. Water can easily flow through this but the salt we dissolved in it can’t. Cells are filled with lots of little molecules so water usually flows into the cells and fills them to dilute the liquid. But when we have lots of salt in the water, there are more particles in the water outside of the potato cells than inside so the water leaves the cells.

When cells are filled with water they are quite rigid and packed closely together making a fairly sturdy chip. When the cells are dehydrated, they are smaller leaving space between cells, allowing the chip to bend without snapping.

Osmosis is used in all plants – not just when you cut them up and put them in a bowl of water! Plants use osmosis in their roots to allow water to move from the soil into their roots.

# #TryThisTuesday: Making coins shiny again

New coins are always bright and shiny but they quickly become dull and tarnished. Today we are going to make our coins shiny again!

You will need 100ml of vinegar, some tarnished copper coins and a bowl.

Pour the vinegar into the bowl and add the salt. Mix until the salt is dissolved.

Try dipping a coin in and holding it there for 5 minutes. See how half becomes really shiny!

Put all your coins in and leave for 30 minutes. If you put lots of coins in the vinegar may turn green.

Make sure you rinse all the coins with clean water.

### The Science

Coins become dirty due to oxygen in the air reacting with the metal to form copper oxide. They become darker as they age as the oxide layer increases. Vinegar is an acid (acetic acid) which can be used to clean up surfaces and remove the unwanted oxides. Acids release positively charged hydrogen atoms, also known as Hydrogen ions (H+) which react with the negatively charged oxygen in copper oxide and produce water (H2O). The copper that was linked to the oxygen dissolves leaving a nice shiny surface.

If your vinegar turned green this is due to all the copper dissolving and producing copper acetate.

### Real World Applications

Iron that is used to make cars, trucks and boats can also react with the oxygen in the air and oxidise, producing rust. If a car gets rusty, mechanics can use phosphoric acid  to remove it. It reacts with the rust, removing the oxide and replacing it with a layer of iron phosphate. This also protects the metal from rusting further.

Phosphoric acid is also found in coca cola, which is why it is so good at dissolving your teeth!

# #TryThisTuesday: Oil and Water

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

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’.

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.

### 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: Valentine’s Day Optical Illusion

Happy Valentine’s Day! Love can confuse your brain, and so does this week’s Try This Tuesday.

You don’t need any equipment to try this experiment at home – you just need to stare at your screen, or more specifically the + in the middle of the picture below. You can blink but don’t look away.

If you stare long enough the pink dots should disappear!

### The Science

It looks like the pink dots have disappeared due to a visual phenomenon called Troxler’s fading or Troxler’s effect. if you fix your eyes on a certain point, then anything in your peripheral vision will fade away and disappear after about 20 seconds. In this experiment our sight was focused on the + in the middle of the screen and the the pink dots in your periphery slowly fade and finally disappear. It works especially well in this experiment at there is such low contrast between the light pink dots and the grey background.

This is a type of optical illusion. If you want to see another, have a look at our spinning disk Try This Tuesday.

# #TryThisTuesday: Book Pulling

You’ve probably got exams coming up, maybe you’re supposed to be revising now, chances are you’re surrounded by textbooks. If so here is a quick little experiment you can try.

All you need is two large books with lots of pages, around 200 or so.

Start by interleaving the pages one on top of the other to sandwich the books together, like so:

This doesn’t require any kind of glue or tape but the two books should now be securely stuck together. Challenge your friends to try to pull the books apart – no matter how strong they are, they won’t be able to do it!

So if there’s no glue, why is this? It’s all because of friction. Friction is a force that occurs when one object moves over another – it is the resistance that is felt. When you try to pull the books apart there is friction acting on each page opposing the movement. If you consider there are over 200 pages, this force is multiplied and so becomes super strong!

When you pull the books the pulling motion squishes the pages in the middle with a greater force, this in turn makes the force of friction greater as it acts to oppose this force. So the harder you pull, the more difficult it is to separate the books!