# #TryThisTuesday: Skipping Stones

During our time as STEM Ambassadors, we’ve visited several beaches together. From Newcastle in Northern Ireland to Clear Water Bay in Hong Kong and even beaches closer to home in Whitley Bay and Tynemouth, we always ended up skipping rocks somewhere!

But how do we do it!? Why don’t the rocks just fall into the water?

The key is to get a nice flat rock and throw it quickly at the right angle. The large surface area allows the stone to bounce off the water’s surface.

You need to throw it fairly hard to give it enough speed to gain momentum before it hits the water. When the rock hits the surface of the water it pushes the water down whilst the water pushes the rock up. If the force pushing the stone up from the water is greater than or balances the weight of the stone then it will bounce on for another skip rather than sinking. This is why it helps to have a nice small stone.

It is also important to get the right velocity. Velocity is the speed of something in a give direction. So we have the speed covered, now for the direction. Scientists have discovered that the optimal angle at which the stone should hit the water should be around 20 degrees. As you probably won’t be able to measure this on a causal day trip to the beach, just aim to throw the stone sideways rather than up or down.

Hopefully you’ll manage more than my measly two skips. Try beating the world record of 88 skips in a row!

# #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.

This week we’re making ice cream but instead of using an ice cream machine, we’re going to make it using science!

You will need:

• Two Ziploc bags – one small, one large
• 100ml double cream
• 50ml milk
• 40g sugar
• Vanilla extract
• Ice
• Salt

1. Measure out the milk, cream and sugar and place them into the smaller Ziploc bag.
2. Add a dash of vanilla extract  then zip up the bag.
3. Fill the larger bag 2/3 full with ice.
4. Pour a generous amount of salt onto the ice.
5. Making sure the small bag is tightly zipped up, place it inside the bigger bag with the salt and ice.
6. Gently shake the bag for 5-10 minutes, be careful not to rip the bag!
7. Leave the ice cream to sit inside the ice and salt bag for another 10 minutes
8. Open up your bag and enjoy!

Try making different flavours of ice cream by swapping the vanilla extract for strawberry or mint extract or even cocoa powder for chocolate ice cream. You could also try adding chocolate chips.

### How does this work?

Water, as I’m sure you know, freezes to make ice at 0oC. But your freezer at home is around -18oC, so how are we making the ice cold enough to freeze your creamy mixture? The secret is in the salt.

Ice is in a constant state of melting and refreezing and melting and refreezing. When we add salt, the salt particles block the path of the melted ice, stopping it from freezing back on to the rest of the ice but ice can still melt. Therefore more ice is melting that freezing.

Now you may be thinking that surely if the ice is melting that means it is getting warmer? It’s actually the opposite. For ice to melt it needs to break the bonds that are formed between the H2O molecules. This breaking requires energy which it gets in the form of heat. When a molecule melts away a bond is broken, taking heat away from the surrounding, causing the temperature to drop.

This is also the reason that salt is put on icy roads – it stops water forming ice.

# #TryThisTuesday: Guess The Flavour

For this Try This Tuesday all you will need is some starburst or chewy fruit sweets.

Close your eyes and pick a starburst at random without looking. Unwrap it with your eyes closed.

Hold your nose and eat the starburst, make sure you keep holding your nose the whole time.

Can you guess the flavour without looking at the colour of the sweet or the wrapper? You might get some of them wrong!

If you let go of your nose halfway through chewing, you might suddenly be able to taste the flavour.

### The Science

Smell and taste are really closely linked, so it is really hard to guess the flavour of the starburst when you hold your nose. About 90% of what we taste is due to smell. Both senses use similar receptors and rely on the same molecules to send messages to the brain about what you can taste and smell. Flavour is actually a mix of taste, smell, texture and other cues like temperature.

It is also important to close your eyes when you eat the starburst, as you can make unconscious links between colour and flavour. Our brain is really good at picking up associations such as a purple coloured sweet is likely to taste of blackcurrant. When the colour makes us expect something to taste a certain way, we taste what we expect unless it’s really different.

This colour association affects some people worse than others,  the pathways to the brain can get crossed over causing synaethesia. This might mean that when they see yellow – they taste lemon.

# #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: DIY Sci-Fi Laser Sound

This week we will show you how to create sci-fi laser sound effects using a slinky and a cup.

The first step is to try and listen to the noise a slinky makes on its own by moving it up and down so the bottom of it bounces off the floor as shown in the picture below.

The next step is to place the cup in the top of the slinky as shown below and try the same movement.

### The Science

Sound is actually particle vibrations and travels in waves. This means it relies on particles colliding to transfer the sound energy. In a gas such as air the particles are really spread out which means they are less likely to collide. In solids the particles are much closer together which means the particles collide a lot more and the sound energy is transferred more effectively.

This is why the sound is much louder when the sound waves travel through the solid cup as opposed to the air. Rumour has it that they actually used this same technique to make the laser sound effects in the original Star Wars movies back in 1977.

# #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: The Peg Game

This week we will show you how to play a game that you will never lose! For this you will need 12 pegs and a piece of material. Clip all 12 of these pegs in a line along the material.

The rules of the game are simple:

• There may only be 2 players.
• Each player takes it in turns to remove 1, 2 or 3 pegs from the material.
• The winner is person who removes the last peg.

If you follow 2 key steps then you can ensure victory every time. Firstly always let your opponent go first. The second step is to remove enough pegs so that the combined total of the pegs you remove and the pegs your opponent removed on their last turn adds up to 4.

For example if your opponent removes 1 peg then you will remove 3 but if your opponent removes 3 pegs then you should only remove 1 peg.

If you do this then no matter what happens the most pegs you will ever have on your last go will be 3 so you will always win!

### The Science

This game is actually based on good old times tables and more specifically the 4 times table. If each round adds up to 4 then the 12th peg will always be removed by the person finishing the round as 12 is a multiple of 4.

This means the game could be played with even more pegs as long as the total number of pegs is a multiple of 4.

# #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!