### scientific method

a series of steps followed to solve problems, including collecting data, formulating a hypothesis, testing the hypothesis, and stating conclusions

### system

a set of particles or interacting components considered to be a distinct physical entity for the purpose of study

### hypothesis

an explanation that is based on prior scientific research or observations and that can be tested

### model

a pattern, plan, representation, or description designed to show the structure or workings of an object, system, or concept

### theory

an explanation for some phenomenon that is based on observation, experimentation, and reasoning

### SI

Le Systéme International d'Unités, or the International System of Units, which is the measurement system that is accepted worldwide

### weight

a measure of the gravitational force exerted on an object; its value can change with the location of the object in the universe

### density

the ratio of the mass of a substance to the volume of a substance; often expressed as grams per cubic centimeter for solids and liquids and as grams per liter for gases

### conversion factor

a ratio that is derived from the equality of two different units and that can be used to convert from one unit to the other

### percentage error

a figure that is calculated by subtracting the accepted value from the experimental value, dividing the difference by the accepted value, and then multiply it by 100

### significant figures

a prescribed decimal place that determines the amount of rounding off to be done based on the precision of the measurement

### scientific notation

a method of expressing a quantity as a number multiplied by 10 to the appropriate power