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Mathematics
Integers on the number line
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Place integers on a number line in three contexts (elevation, bank account, temperature) and on a free number line; compare numbers, find opposites and absolute values.
Drag the person, bird or fish from the box into the scene. Sea level is 0 m; below the surface is negative.
Using the keyboard
Select an object or point: Enter places it, arrow keys move it, Delete returns it to the box.
Drag an object from the box into the scene to start comparing.
On a vertical line, a higher point stands for a greater number.
Model notes
- Only integers are used. Ranges shown: elevation −80…100 m, balance −100…100 thousand dong, temperature −70…40 °C (−80…100 °F), Number line ±10, ±30 or ±100. These are limits of the resource, not of the integers: a number line goes on forever in both directions.
- When an object or point is dropped, its position is rounded to the nearest integer; an exact half rounds away from 0 (2.5 becomes 3; −2.5 becomes −3). Two points on the Number line, or two objects in Elevation, never share a number: the one dropped last moves to the nearest free number. Two accounts or two thermometers may show equal numbers.
- The comparison lists the numbers in increasing order with < and in decreasing order with >. With only one point, it is compared with 0. Two equal numbers use =; among three numbers, an equal pair uses ≤ or ≥ to keep the chosen direction.
- Temperatures are 2001–2020 monthly means from the MERRA-2 reanalysis provided by the NASA POWER project, for a grid cell of about 50 km around each place, not readings of a weather station in the city, so they may differ by a few degrees. Readings are rounded to 1 degree; °F = round(°C × 9/5 + 32) from the unrounded °C value.
- The places are arranged from north to south by latitude, with an equator line; this is not a map. Card colours only hint at the temperature; read the numbers on the line and the thermometers.
- The balance is the money in the account, in thousand dong; a negative number means debt. The jar grows with |balance| only as an illustration.
- The elevation scene is an illustration: only the height above or below sea level is measured; the horizontal position of an object has no meaning. The absolute value of an elevation is its distance from sea level.
- The absolute value |a| is the distance from a to 0, so it is never negative; the opposite −a lies symmetric to a about 0.