# Unit 3 Vocab

Unit 3

### Proportional

When quantities have the same relative size. In other words they have the same ratio.

Example: A rope’s length and weight are in proportion. When 20m of rope weighs 1kg, then:
• 40m of that rope weighs 2kg
• 200m of that rope weighs 10kg
etc.

### constant of proportionality

See Slope of a line In a proportional relationship, the values for one quantity are each multiplied by the same number to get the values for the other quantity. This number is called the constant of proportionality.

### Rate Of Change

See Slope of a line The rate of change in a linear relationship is the amount changes when increases by 1. The rate of change in a linear relationship is also the slope of its graph. In this graph, Y increases by 15 dollars when X increases by 1 hour. The rate of change is 15 dollars per hour. ### Linear Relationship

A linear relationship between two quantities means they are related like this: When one quantity changes by a certain amount, the other quantity always changes by a set amount. In a linear relationship, one quantity has a constant rate of change with respect to the other.

The relationship is called linear because its graph is a line.

The graph shows a relationship between number of days and number of pages read.

When the number of days increases by 2, the number of pages read always increases by 60. The rate of change is constant, 30 pages per day, so the relationship is linear. ### Vertical Intercept or Y-Intercept

The vertical intercept is the point where the graph of a line crosses the vertical axis.

The vertical intercept of this line is (0,-6) or just -6. 