Fun with Goop
Students will be able to measure solids and liquids using traditional devices.
Measuring is something that we do all the time on a daily basis. Cooking seems to be the most obvious example where measurements help to ensure our final product is what we expect. What would happen if we tried to bake a cake and didn’t put enough flour, or sugar? This activity is a simple introduction to using measuring cups.
Goop is often referred to as a 'non-Newtonian' substance because it does not behave as Newton's Third Law of Motion states (for every action, there is an equal and opposite reaction). Applying this principle, you would expect Goop to 'splash' when you 'smack' it with your hand. However, when you try this, Goop does not splash, it becomes a solid substance for a few moments. Scientists explain this as follows: uncooked cornstarch particles are structured in both crystalline and non-crystalline arrangements. When slowly mixed with water, the non-crystalline structures of cornstarch absorb most of the water. When you smack or stir it rapidly, it increases the temperature and pressure on the mixture which causes more non-crystalline structures to form. These new non-crystalline structures absorb more water and the mixture becomes thicker, hence the appearance of a solid. When you discontinue the pressure, the number of non-crystalline structures decreases and water is released, creating the 'soupy' mixture. This is pretty technical and not at all necessary for the activity; the material is just a lot of fun to play with!
- 3 parts Cornstarch
- 1 part Water
- Measuring cups and spoons
- Cookie tray or bowl or pie plate
- Smocks (optional)
- Food colouring (optional)
For each child or group of children, have them measure out 1 cup of cornstarch using a measuring cup. This can go in a bowl, or container of some sort. Then have them measure 1/3 cup of water and add to bowl of cornstarch. Food colouring can be added using spoon measure, if desired. Then let them mix it up with their hands. As they’re scooping it up and letting it run through their fingers, ask them if they think it’s a solid or a liquid. It should feel like a solid as they pick it up and feel like a liquid as it runs through their fingers.
- Can you recall a time where you had to measure something?
- What devices can be used to measure somebody’s height?
- What device can be used to measure how long it takes to drive to school?