Number 28: Homemade Magnetic Slime

Fancy making some magnetic putty? There have been a few videos of the stuff doing the rounds on Youtube and I thought it  would be cool to see if I could make some of this fabulous stuff from scratch. Mines a bit more like slimes so it slithers and slides towards magnets like this..

And it consumes magnets like this...

(3 minutes compressed into 8 seconds with the help of imotion app.)

You’ll need:

• A large bottle of PVA Glue
• Borax (some supermarkets or hardware stores stock this, or get it online)
• Black iron oxide (its used in cosmetics and tattoo inks so its harmless)
• Zip lock freezer bag
• Neodymium magnets
• Some plastic cups.

Safety: 

• Borax is toxic in large amounts, so don’t swallow it. And wash your hands after handling the slime.
• The neodymium magnets are VERY strong. They can shatter if they fly towards each other and will pinch if you trap your skin between them. They should only be handled by a responsible adult. Be very careful with them and follow the safety instructions on the packet. 
• AND unless you want to see an adult explode DON'T get the slime stuck in the carpet!

What to do:

1. Dissolve 1/2tsp of borax in 1/2 a cup of water (its not very soluble so don’t worry if some of it doesn’t dissolve)
   
   
   
2. Pour out 1/4 of a cup of PVA into a cup, add the same amount of water.
3. Add 4 teaspoons of iron oxide to the PVA/water and mix it all together. The iron oxide is quite a fine powder and can make quite a mess so be careful.
   
   
   
4. Pour the PVA/iron oxide mix into the zip lock bag.
   
   
   
5. Add the borax solution to the zip lock bag. Flatten the bag so there isn’t any air in it and then zip it up.
   
   
   
6. Massage the contents of the bag. The liquid mix will slowly turn to a black slime. After 5-10 minutes you should be able to take it out of the bag. If its still quite sticky then leave it in the bag for another 5-10 minutes.
   
   
   
7. Once the slime is ready put in on a plate and start experimenting with the magnet. You could try rolling a small bit of slime into a sausage shape and then putting the magnet near it or stick the magnet in the middle of the goo. Have fun!
8. If you want to try some of those time-lapse videos download imotion for Apple or Android. And why not upload it to Youtube and then post the link in the comments below.

What’s going on:

First how does the liquid mixture turn into slime? Well, the PVA glue is made of long thin molecules and together they make a thick liquid. The borax connects the PVA molecules together making a network of connected molecules, which resembles a 3D network, turning it from a pourable liquid in a putty. 

Meanwhile the iron oxide* particles have magnetic properties which makes them align  in the magnetic field of the nearby magnet. Then they are drawn to the magnet, dragging the slime with them.

If you are feeling lazy you can buy some ready made putty (but where’s the fun in that). And besides if you make it yourself you can muck around with the PVA to water ratio to make it more or less runny. More water makes it more slime-like, more PVA makes for a firmer putty.

And if you just want some classic slime then leave out the iron oxide and add some food colouring instead.

* The most common form of iron oxide is rust with a chemical formula of Fe₂O₃. Black iron oxide is Fe₃O₄.

Number 12: The world's simplest electric motor

I saw this astonishingly simple motor described over at the fab proton's for breakfast blog and had to have a go.

All you need is:

• A small stack of 12mm diameter disk magnets (I get mine from emagnets)
• A 1.5V AA battery
• A length of stiff but bendable copper wire
• A penny 

Safety:

The magnets are very strong. Watch out they can fly together and shatter. 

What to do:


1. Stick the magnets onto the negative end of the battery.

2. Place the penny on the top of the battery.

3. Bend the wire so that it balances on the top of the penny whilst the other end only just touches magnets.

4. And watch it spin!

What's going?

When the copper wire touches the magnet a circuit is completed and electricity runs through the wire. When electricity passes through a wire it generates a magnetic field. This then interacts with the magnets at the bottom of the battery (in the same way as opposite poles of a magnet repel each other) and the who thing spins. Hey presto the world's simplest motor.

Number 7: The magnetic grape

You remember how in school your teacher told you that only things with iron in them are magnetic; spoons, nails that sort or thing? Well your teacher didn't get that quite right. Because it turns out that  everything is magnetic to some extent. Even grapes. And that's why this happens:

If you want to try this yourself..

You'll need:

• 2 grapes
• A wooden skewer (NOT A STEEL ONE)
• A pin
• Something to stick the pin through so that it points upwards on a stable base. I used an old film canister, but bit of cork would do just as well.
• A neodymium magnet. The stronger the better but you probably want one with at least 20 Kg pull.

Safety:

THIS IS REALLY IMPORTANT

The neodymium magnets are really powerful. So...

1. Don't let kids play with them.
2. Don't put them near your credit cards, phone, watch or any other electrical equipment.
3. Don't put 2 magnets anywhere near each other because they'll fly towards one another, shatter and send chunks flying.
4. If you have any medical implants don't go anywhere near them.
5. Read the safety instructions that come with the magnets.

What to do:

1. Push the 2 grapes onto either end of the skewer

2. Push the pin through the cap of film canister, so that its pointing upward. Put the cap back on the canister.

3. This is the tricky but. You need to balance the skewer and grapes on the point of the pin. If you get close then adjust the balance by pushing one grape further onto the skewer.

4. Once you've managed that just put the edge of the magnet near one of the grapes and watch them spin.

What's going on?

There are actually numerous types of magnetism. At school we only learn about ferromagnetism. Then there's paramagnets (which are attracted to ferromagnets) and diamagnets (which are repelled by ferromagnets). These 2 types of magnetism are much weaker than ferromagnets so you generally can't see the effect. Which is why you need a set up like this and a powerful magnet to observe it.

Since the water in the grape is diamagnetic its repelled by the strong ferromagnet near it and that makes the grapes spin on the pin. 

You can demonstrate the same principle another way shown here.

Incidentally this effect is central to how MRI scanners in hospitals work.