Milk Food Coloring And Dish Soap Experiment ~ Incredible Science

Today at school we completed this investigation. The investigation we followed is below.

Tie-Dyed Milk

Introduction

Liquids
like water and milk have a property known as surface tension, due to the
cohesive forces of the liquid's molecules.

Look
closely (you can use a magnifying glass) at the edge of the surface of water in
a clear glass. Do you notice how the very edge of the water appears to rise up
the side of the glass?

That's
because the surface tension of the water is actually pulling the water
away from the glass inward toward the center of the surface.

Soap will
reduce this surface tension. Let's see what happens!

Safety

• Make sure you have an adult
  helping you.
• Do not drink the milk after
  you have put the food colouring and soap in it!
• Do this experiment near the
  sink so that when you're done you don't spill milk and food colouring all
  over the floor.

 

Prediction- What I think will happen? Why?
______________________________________________________________________________________________________________________________________________________________________________________________________

Equipment

• A shallow dish -
• Milk - The higher the fat
  content the better.
• Food colouring - Four
  different colours will be more colourful.
• Liquid dish soap.
• A toothpick or small straw
  might be helpful, too.

Directions

1. Pour a layer of milk in the
   dish about (1 cm) deep. Room temperature milk works much better than cold
   milk.
2. Carefully put one small
   drop of each of the four food colours onto the surface of the milk,
   widely separated, and not in the center of the dish (less is better
   than more!). Something like this:
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
3. Get ready to watch what
   happens! Very carefully drop one drop of dish soap onto the surface
   of the milk in the center of the dish. (Be careful not to add the soap
   directly on top of the food coloring. You may want to dip a toothpick in
   the dish soap so that a small drop of soap remains on the end of the
   toothpick, then touch the drop to the surface of the milk.)

Observations

• What happens to the food
  colouring when you first put it on the milk?_____________________________________________________________________________________________________________________________________
  

Why do you think that is?_______________________________________________________________________________________________________________________________________

• What happens when you add
  the drop of soap?_____________________________________________________________________________________________________________________________________
• What direction does the food
  colour move when you first add the drop of soap?_____________________________________________________________________________________________________________________________________
• What direction does the food
  colour move after the experiment has been running for a while?
  __________________________________________________________________________________________________________________________________________
• Does the movement go on
  forever? What happens?_______________________________________________________________________________________________________________________________________________________________________________________________________
• What happens if you add another
  drop of soap after the colours have stopped moving?___________________________________________________________________________________________________________________________________

Pictures-
draw 2 pictures of what is happening in the bowl

 

 

 

 

What's Happening?!?

You
probably first noticed that the drops of food colouring just sat on the surface
where you placed them. That's because food colouring is less dense than milk,
so it floats on the surface, and the colours do not mix because you didn't stir
the milk.

Then the
action began with a drop of soap! The soap reduces the surface tension of the
milk by dissolving the fat molecules, which is why fattier milk works better.
The surface of the milk outside the soap drop has a higher surface tension, so
it pulls the surface away from that spot. The food colouring moves with the
surface, streaming away from the soap drop. Due to the convection that results
from the moving surface, the food colouring may be drawn down into the liquid,
only to appear rising again somewhere else. That's why it's best to use a clear
bowl so you can see what's happening.

As the
soap becomes evenly mixed with the milk, the action slows down and eventually
stops. Addition of another drop of soap may start the process again.

 Photos of us working to come next week.