# #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.

### Can you figure out how to make a colourful bunch of “flowers” out of your kitchen roll using this method? Check back for next week’s Try This Tuesday and we will show you!

As we have reached the end of the school year, here is a little round up of some of our favourite questions that children have asked us during STEM workshops.

### 1. Why doesn’t the energy ball give you an electric shock?

The energy ball is a little device we have that looks like a ping pong ball with two metal strips on top. Inside there is a light, a buzzer and a battery. If two people touch one metal strip each and then with their other hands touch each other, the ball lights up and buzzes. This works because we are conductors of electricity – electrons from the battery flow through us and back into the ball to complete the circuit.

The reason you don’t feel a shock when touching the energy ball because there isn’t enough electricity flowing through you to be able to feel it, and certainly not enough to harm you!

### 2. What do plants poo and wee? – St Wilfrids, Blyth

All living things have seven things in common – movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. The sixth one, excretion, is a scientific word for producing waste. In humans, and many animals, that is our poo and our wee. They are the leftover waste products that our body doesn’t need so gets rid of.

Plants are living things, just like us, but you may have noticed they don’t poo or wee like we do. Rather than eat food like us, they make their own through photosynthesis. This produces a waste gas called oxygen which we breath in. Plants excrete oxygen rather than poo or wee.

### 3. Why does the moon control the sea? – Grange First School

Gravity is the force that keeps us close to the Earth, all really big things like planets and stars have a gravitational pull that attracts things near by. Because the moon is so big and so close to Earth it has quite a strong gravitational pull on our planet. The moon causes the water in the oceans facing it to pull towards it, resulting in a high tide. The pull of the sun’s gravity and the Earth’s own gravity also have an effect on the tides.

### 4. I’m the only one who can touch their nose with their tongue, is that because of my genes? – St Marys, Jarrow

Touching your nose with your tongue is known as Gorlin’s Sign. It is associated with a genetic disorder but not everyone that can do it has the disorder. About 10% of people without the disorder can touch their nose with their tongue and it does not appear to be due to genes you have inherited from your parents.

### 5. Why do we get goosebumps? – Billingham South Community School

We often get goosebumps when we’re cold, but they don’t do much to help us warm up, so why do we get them? Before we evolved to be modern humans, our ancestors were much hairier, we they got cold, getting goosebumps would cause their hairs to stand on end. As they had much more hair than us, they were able to trap a layer of air in the hair by doing this, providing them with extra insulation to keep them warm.

Although goosebumps are no longer helpful to us, we haven’t lost the trait through evolution because it doesn’t harm us. Therefore if a person was born with a mutation in their genes meaning they didn’t get goosebumps, they wouldn’t be at an advantage because of it so the non-goosebump genes wouldn’t necessarily be passed on more than the goosebump genes.

# #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.