Tag Archives: cream

#TryThisTuesday: Homemade Ice cream!

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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

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  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.p1020738-3
  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!

p1020740-2Try 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: Slime!

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slime

With Halloween coming up, what better time to make some of your very own slime?

It’s super easy and quick to make – you just need to mix water and cornflour! Start with a little bit of both, if it seems too runny you can add more cornflour and if it becomes a solid then add more water.

You can also add food colouring and glitter if you want to add some sparkle to your slime.

The slime should become a consistency that appears to be a liquid but if you hit it or try to stir it quickly it becomes a solid – so which is it?

Liquid or Solid?

Slime isn’t actually a solid or a liquid – it is a non-Newtonian fluid, this is a fluid that changes its properties when a stress or force is applied.

The slime we’ve made is a particular non-Newtonian fluid called oobleck (yes it’s a funny sounding word – that’s because it is derived from a Dr. Seuss book). The particles of cornflour don’t dissolve in the water, they become suspended in the water and repel each other. Mechanical stress, such as stirring quickly provides energy that overwhelms the repulsive forces, causing the particles of cornflour to temporarily stick together. When the stress is removed, the repulsion returns and the slime becomes liquidy again.

More Non-Newtonian Fluids

1. Custard behaves just like oobleck, in fact if you filled an entire swimming pool with custard, you would be able to walk across it!

2. Ketchup is almost the opposite of oobleck – it become thinner and runnier under impact, that’s why it helps to bang the end of a ketchup bottle when you’re struggling the get some out.

3. Whipping cream acts differently when under a constant and prolonged stress, such as whipping. If you whip cream for long enough it will appear to go from liquid to solid as it becomes whipped cream.

4. Honey similarly needs prolonged stress to change it’s properties. When you stir honey, it will become more like a liquid than a solid.

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