# Liquid Nitrogen Ice Cream

Liquid nitrogen, if you’re not familiar with it, is a liquid that is commonly used to preserve tissue samples, remove warts, help keep MRIs cool, or cool high performance computers. The reason for this is its incredibly low temperature: -196 C (compare this to ice, which is 0 C, or dry ice, which is only -78.5 C…).

And this is what makes it perfect for creating ice cream in a matter of minutes… the rapid freezing also results in smaller ice crystals, meaning a much smoother taste. See below for some easy to follow instructions.

You will need a food processor, spatula, access to liquid nitrogen and suitable PPE!

Ingredients:

• 1 cup milk
• 1 cup double cream
• 5 tablespoons sugar
• 1 teaspoon vanilla
• 1 cup of strawberries (or other fruit to taste)
• 1 litre liquid nitrogen

Mix all the ingredients in the food processor and whisk for a few seconds. Start gradually pouring in the liquid nitrogen whilst whisking, keeping a spatula on the side of the bowl to break up any chunks of cold mixture. Eventually the mixture will freeze into a smooth, ice cream texture.

Caution: If you go too fast, or the bowl is too small, the rapid boil off of liquid nitrogen will cause your ice cream to bubble over the side of the bowl! (see above picture of the aftermath…)

Safety note about liquid nitrogen: Because it is so cold, and will expand to about 70 times its volume when it warms up, there are 3 major safety concerns when mixing liquid nitrogen and food:

1. Wear appropriate gloves and clothing when handling, to avoid cold burns. If this does happen, hold the affected part under cold water for a few minutes.
2. Make sure to perform the activity in a well ventilated room. If you are unsure there are calculators online that will let you determine the drop in relative oxygen content if your dewar of liquid nitrogen were to all boil off at once.
3. Never eat or drink anything where the liquid nitrogen has not boiled off. This is simple to check as the ‘vapour’ that boils off when you add it to the ice cream will have stopped. Also, the ice cream would be too stiff for the food processor to mix if you had cooled it to -196 C.

# STEM Community Day at Loughborough, 16th March 2019

Every year as part of British science week Loughborough University opens its doors to the community to host a range of STEM based activities. This year there are several activities organised by my group and in coordination with the UG reps:

If you’re in the area drop by for a chance to get messy, learn something new, or just have some fun! I will be posting summaries of each activity over the next few weeks.

# Science in the Park 2019 – Light Painting

I have added rough times for the images below. They are organised by group(s) for the two separate SD cards that were used. If you do not see your photo in the top, please make sure to scroll through to the bottom for the other SD card.

# “I am a Physicist” Challenge

The East Midlands Branch covers Derby, Leicester, Lincoln, Loughborough, Northampton and Nottingham, with centres based in Derby, Leicester, Loughborough and Nottingham. We organise a full programme of lectures, meetings and conferences in the East Midlands and work locally to promote physics, physics education and public understanding of physics.

The IOP East Midlands branch have recently launched the ‘I am a physicist’ Girlguiding badge and resource designed to introduce girls to the fascinating world of physics in a way that is accessible, fun and educational.

Currently being piloted in Nottinghamshire, the badge is open to all Girlguiding sections with age appropriate activities from the youngest Rainbow at 5 to the oldest Ranger at 18. We hope leaders will enjoy the activities too.

The challenge is in four sections:

• Section 1: Experience
• Section 2: Create
• Section 3: Investigate
• Section 4: Meet, visit, community

The pilot will run until the end of the year during which time workshops and events will be run to support leaders, such as a stand at Science in the Park at Wollaton Hall and Deer Park next weekend, or at County Day on 23 March. Look out in the Girlguiding Nottinghamshire diary for further dates.

http://www.iop.org/activity/branches/midlands/east-midlands/

#Iamaphysicist

@physicsnews

@girlguidingnott

@IOPEastMidlands

@IOPMidlands

# Science meets art: painting with ferrofluid

Ferrofluid, as described here in greater detail, is a suspension of iron oxide nanoparticles that are so small, that they align themselves immediately with an applied magnetic field (superparamagnetism). This results in a spiky pattern that gives an indication of the position of magnetic field lines, which I like to refer to as the ‘hedgehog’.

If you inject a water based paint into the ferrofluid, when a magnet is held on the other side, you will be able to form domains of colour suspended in the fluid – as seen above.

# Double Rainbow

Can you see the double rainbow?

Ever noticed how the order of the colours changes for the second rainbow (red – yellow – green – blue – violet…)

Typically rainbows are formed when light is refracted (bent) through a raindrop.

A double rainbow forms when light is refracted twice in a raindrop, and occurs commonly when the sunlight is low in the sky. See here for more.

# Useful Resources

I will be adding resources here as I find them – mostly Maths and Physics themed.

## Online Mathematics Course

Loughborough’s Mathematics Education Centre runs a free, three-week MOOC – Getting a Grip on Mathematical Symbolism – designed for those students aspiring to become scientists or engineers but who lack mathematical confidence.

It will run again on the FutureLearn platform starting May 8th. Registration is open now:

https://www.futurelearn.com/courses/mathematical-symbolism

The course is designed for students who have some engineering or science knowledge gained through vocational qualifications or through workplace experience but who perhaps have not studied mathematics formally since leaving school. It will be appropriate for those who lack confidence but who need to establish a bedrock of knowledge in order to further their education.
This is a foundation, entry-level course and is not intended for those who already possess recent post-GCSE mathematics qualifications. It is highly recommended for those students going to university who have not studied maths beyond GCSE. Please share when appropriate.

Note that it is planned to run this course again shortly before the start of the new academic year in September.

Magnet Academy is an online resource provided by the National High Magnetic Field Laboratory — the largest, most high-powered magnet lab in the world. It has a wide selection of useful tutorials about electromagnetism for ages 5 upwards.

Interactive Magnetic Tutorials

# British Science Week

As part of British Science Week, Loughborough University hosts a ‘Community Day’ event where Loughborough locals are invited on campus to take part in various ‘science based’ activities.

This year it falls on 25th March I will be:

• Coordinating an Electrodough workshop – for which we’re looking for student ambassadors.
• Running a ‘Cold Science’ demonstration with liquid nitrogen.
• Working with the East Midlands Institute of Physics to deliver several ‘busking’ activities –  for which I’m looking for student ambassadors.

If you’re interested in getting involved please let me know.

# Liquid nitrogen

Roughly the same cost (weight for weight) as a pint of milk, it’s a common feature in science fiction films: the nitrogen dewar in the background that might at some point be used to freeze that alien chasing you down the corridor…

But how much liquid nitrogen would it actually take to do this?

Hint: Assume the creature weighs about 50kg and has a heat capacity of 2000 J/K/kg. Liquid nitrogen has a temperature of 77K and latent heat of 199 kJ/kg. For arguments sake, let’s say the creature becomes vulnerable at 250K…

Now let’s add another complication: the Leidenfrost effect. As a coolant, the low boiling point of liquid nitrogen (77K) typically means that it will boil off so fast on contact with another object much hotter than it, that a ‘protective’ layer of air is formed. This will insulate said object from the cooling effects of the liquid nitrogen, for example preventing cold burns for anyone crazy enough to stick their hand in a bucket of liquid nitrogen for a second or two. CAUTION: This effect will not stop you from getting burnt as more nitrogen is added.

For more see Wikipedia entry for liquid nitrogen

# The invisible rod

Challenge: How can you make a quartz rod invisible with some water, sugar and a beaker?

$n_{1}sin(\theta_{1})=n_{2}sin(\theta_{2})$
So you might imagine that if we can change the rod, or the liquid itself, so that light entering from behind the beaker does not refract further on entering the quartz rod, we can effectively make the quartz rod invisible. To do this we want to match up the refractive indices ($n_{1}, n_2$).