# Lesson 4: Solid, Liquid, Gas: What's the Difference?

## Getting Started

In this lesson, you will begin to look more closely at the three states of matter. Keep in mind that solids, liquids, and gases represent different states of the same element or compound and that each state of matter has its own traits. The three states are defined as follows:
• A solid is a material that keeps its shape and resists change in shape at room temperature and normal atmospheric pressure. (Atmospheric pressure is the downward pressure exerted by the weight of the atmosphere.)
• A liquid is a substance that flows, that is a fluid at room temperature and normal atmospheric pressure, and whose shape can be changed. Unlike a solid, the volume of a liquid can be changed.
• A gas is a substance that is neither a solid nor a liquid at ordinary temperatures and has the ability to expand.
• Another state of matter is known as plasma. Plasma is a gas made up of ions (electrically charged atoms) and electrons. Plasma is abundant in the Sun and stars. On Earth, it is found in lightning, neon signs, fusion reactors, plasma television displays, and more.
In today's lesson, you will be challenged to imagine and illustrate different states of matter. You will be asked to make connections among the three classical states of matter, the conditions necessary for the states to occur, and what each state of matter will look like at the atomic level.

### Stuff You Need

• construction paper (kit)
• glue stick
• hole punch

• Why does matter "behave" the way it does in different circumstances?
• What patterns can be observed in elements?

### Things to Know

• atmospheric pressure: the downward pressure exerted by the weight of the atmosphere
• solid: a material that keeps its shape and resists change in shape at room temperature and normal atmospheric pressure
• liquid: a substance that flows, that is a fluid at room temperature and normal atmospheric pressure, and whose shape can be changed
• gas: a substance that is neither a solid nor a liquid at ordinary temperatures and has the ability to expand
• state of matter: a state in which matter can exist, depending on temperature and pressure (the states are solid, liquid, gaseous, and plasmatic)
• plasma: a gas made up of ions and electrons; found primarily in the Sun and stars
• melting point: the temperature at which a substance changes from a solid to a liquid
• boiling point: the temperature at which a heated liquid turns to gas

### Skills

• Know that the states of matter (solid, liquid, gas) depend on molecular motion. (S)
• Know that in solids the atoms are closely locked in position and can only vibrate. (S)
• Know that in liquids the atoms and molecules are more loosely connected and can collide with and move past one another. (S)
• Know that in gases the atoms and molecules are free to move independently, colliding frequently. (S)

### Introducing the Lesson

In this lesson, your child will be challenged with the abstract idea that energy determines which state of matter is present. Although this lesson does not focus specifically on energy, the activity is designed to challenge your child to imagine that matter is made up of atoms that are interacting with one another and that these interactions are influenced by the amount of energy present.

Note: In Day 2 of Lesson 5, your child will need to work with ice. To prepare for this, please freeze at least two small plastic cups of water that can be used for the activity.