My 7 yo was wondering, what state of matter is peanut butter? He decided it’s both solid and liquid. According to the TSA, it’s considered a liquid! We could think of other materials that could be described similarly such as glue, or jello. We would love to know the explanation of what state of matter is strong, sort of liquidity substances are?
Your son has recognized a difficulty with defining everything as solid, liquid, or gas. Congratulations. Yes, there is a broad spectrum of “consistencies” between the most liquid and solid. It is a property known as viscosity. It is measured as the amount of time it takes the material to flow through a given opening, or the pressure needed to force it through.
There is a whole field of specialized science/product manufacturing dealing with how to give things the desired viscosity for a given use. Think of tooth past, skin lotion, engine oil, paint. An added complication is that viscosity of most things changes gradually or markedly with temperature. I left this out of the text to avoid the extra complication at the beginning level, but I am happy to see that your son recognized it.