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!
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:
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.
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.
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.
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:
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.
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.
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.
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:
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.
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…
Challenge: How can you make a quartz rod invisible with some water, sugar and a beaker?
Answer: Snell’s Law
If we take something that is typically transparent (i.e. the quartz rod) you can normally see it quite clearly when placed in a liquid, by the way in which light is bent as it passes through.
This ‘bending’ of light – refraction – can be described by Snell’s law:
where ‘n’ is the refractive index of the material.
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 ().
With water, as you add more and more sugar the refractive index increases, until finally it approaches that of quartz ~1.46.