Bread clip speed boat

Float a breadclip in milk, add a drop of detergent and believe it or not, you’ve got yourself a groovy little speedboat that really moo-o-o-ves! 1. Pour some full cream milk into a shallow plate (be a bit sparing - depth isn’t critical). 2. Carefully float a bread clip near the edge of the plate. 3. Squeeze a drop of detergent into the little hole and watch what happens. Your bread clip goes zooming around the plate! Note: When your boat stops, just add more detergent – use a toothpick or match to turn your breadclip if it gets stuck. 4. If you like, use nail clippers to modify your breadclip into a little speedboat shape. 5. Pretty snazzy breadclip eh? 6. And for a very cool effect, add a drop or two of food colouring to the little hole before adding the detergent. 7. You’ll notice that the food colour doesn’t make the boat move like detergent does. 8. When you add a drop of detergent, the food colour comes spurting out of your boat as it races along … cool eh?

what's going on? If you try this experiment with water instead of milk, you'll find it works but only once. You have to rinse the plate and start with fresh water to do it again. With milk however, you just add more detergent and the breadclip starts zooming around again. But let's look at how it works with water first, and why only once. Water molecules are very strongly attracted to each other. The attraction is so strong that you can slightly overfill a glass with water so the surface is just above the rim. Under the surface, every water molecule and its nearest neighbours pull on each other equally in all directions. But there is only air above the surface, so there are no water molecules pulling up. This gives water very strong surface tension. Now detergent molecules don't hang onto water molecules as tight as water molecules hang onto each other. If a detergent molecule gets between two water molecules, the tension between them is slightly reduced. Detergent molecules have two distinct ends which scientists call a head and a tail. The heads are attracted to water molecules and the tails to oil molecules. As you know, oil and water don't mix of their own accord and like oil, a detergent molecule's tail doesn't mix with water either. Scientists have discovered that when detergent is added to water, they 'prefer' to be at the surface with their water loving heads pointing down into the water and their oil loving tails sticking up out of the water. When a drop of detergent is added, the water molecules race across the surface at amazing speeds, decreasing the surface tension as they go. If there are too many detergent molecules to all fit on the surface, the rest start forming little droplets under the surface. These droplets form in a special way so that all the detergent molecule's tails are pointing into droplet with the water loving heads facing out. You could say the oil loving tails are 'hiding' from the water molecules surrounding the droplet. Let's get back to the breadclip. When detergent is added, the molecules race out of the little chamber across the surface of the water until it is completely packed. They decrease the surface tension on the chamber side of the breadclip first. The surface tension on the opposite side of the breadclip is still much greater and as a result, the breadclip is pulled along. Once the surface is filled with detergent molecules, everything settles down again. There's no more room at the surface and any further detergent you add will just form droplets (micelles) under the surface. There is still some surface tension but it is greatly reduced and more importantly, it's the same on all sides of the breadclip … show's over. Now here's what makes detergents so useful. Oil globules usually float to the surface when mixed with water. Introducing just a bit of detergent can help mix oil into the water. Oil droplets attract detergents' oil loving tails so they quickly become covered in a shell of detergent molecules. All the tails latch onto the oil in the middle and all the water loving heads face out. If these droplets (called micelles) are small enough, they can remain suspended in water for a very long time without joining together to form larger globules. An even mixture of oil in water like this is called an emulsion and detergents are emulsifiers. Scientists also call emulsifiers 'surfactants' (short for surface active agents) because they tend to congregate on oil and water surfaces. Now milk is basically an emulsion of little bit of oil (about 4%) in heaps of water (roughly 96%). The oil droplets in milk are covered by a natural proteins. If milk is not homogenised, the droplets are so large that they float to the surface. Homogenisation is a pretty simple process in which the milk is forced through tiny holes under great pressure. This breaks the large oil globules into much smaller droplets which don't join back together and remain evenly mixed in the water (homogeneous means alike or evenly mixed). Adding detergent to milk stirs it up so there is a constant flow from the bottom up to the surface but this is where my explanation runs dry. The surface tension of milk near a drop of detergent in milk is obviously reduced because you can see a flow away from it. But exactly what the detergent is doing to the milk has either not been studied (and published) yet, or I simply haven't managed to find the published results. The detergent might be mixing with or replacing the natural proteins coating the oil droplets. This might constantly alter the surface tension causing a flow but it's all a bit of mystery. We'll just have to wait until some clever chemist with funding and the right equipment performs the experiments to find out. Until they do, we'll remain a species that can send roving robots to the surface of Mars, but can't explain why a little breadclip zooms around the surface of milk. What a wacky mixed up world we live in eh?