# Physics First - Chapter 7

## 24 terms

### atom

the smallest particle of an element that retains the chemical identity of the element

### compound

a substance that contains two or more different elements chemically joined, difficult to separate, can't see the parts that make it

### molecule

a group of two or more atoms joined together by chemical bonds

### mixture

contains more than one kind of atom, molecule, or compound, easy to separate, can see the parts that make it

### element

a pure substance that contains only atoms the same number of protons

### Celsius scale

the difference between the freezing and boiling points of water is 100 degrees (instead of 180). Water freezes at 0° and boils at 100°. Most science and engineering temperature measurements use this measurement because 0 and 100 are easier to remember than 32 and 212. Most other countries use this measurement for all descriptions of temperature, including daily weather reports.

### convection

The transfer of heat through the motion of fluids such as air and water.

### liquid

A state of matter that holds its volume, but does not hold its shape-it flows. The molecules within it are about as close together as they are in a solid, but have enough energy to exchange positions with their neighbors. This flows because the molecules can move around.

### Fahrenheit scale

Water freezes at 32º and boils at 212º.There are 180 Fahrenheit degrees between the freezing point and the boiling point of water. We commonly use this measurement for temperature in the United States; 72° is a comfortable room temperature.

### thermometer

an instrument that measures temperature

### evaporation

The process by which atoms or molecules leave a liquid and become a gas at a temperature below the boiling point.

### heat

The flow of thermal energy or thermal energy that is moving.

### heat of fusion

The amount of energy required to change phases (states of matter).

### heat conduction

The transfer of heat by the direct contact of particles of matter; only occurs between two materials at different temperatures and when they are touching each other.

### gas

A state of matter that flows, but can also expand or contract to fill a container. It does not hold its volume. The molecules within it have enough energy to completely break away from each other and are much farther apart than molecules in the other two states of matter.

### absolute zero

When the temperature gets down to this, molecules have the lowest energy they can have and the temperature cannot get any lower.

### thermal conductor

Materials that allow heat to easily flow through it.

### temperature

a measure of the kinetic energy of individual atoms

### solid

A state of matter that holds its shape and does not flow. The molecules within it vibrate in place, but on average, don't move far from their places

### thermal energy

the sum of all the kinetic energy of the atoms or molecules added up together

### plasma

An ionized gas phase of matter; ie. stars, lightning, and neon-type lights.

### Kelvin

This temperature scale is useful for many scientific calculations because it starts at absolute zero.

### thermal insulator

Materials that do not allow heat to flow through them.