Linear World Cup

A soccer game where you score goals and complete passes by writing the slope-intercept equation of the line connecting your player to a teammate or the goal. Choose a proportional (y = mx) or non-proportional (y = mx + b) mode, play against the computer or a friend, and compete in a full tournament bracket. Controls: type digits for the slope numerator, denominator, and y-intercept, minus key or on-screen button to toggle negative, enter to kick, mouse or the on-screen keyboard to play on any device.

Teaching Notes for Educators

Students type a slope and y-intercept to pass and shoot, and the line for their equation is drawn across the field.

The math: y = mx + b, where the slope m is rise over run, entered as a fraction, and b is where the line crosses the y-axis.
Proportional and non-proportional: Proportional mode fixes b = 0 (y = mx), and Non-Proportional adds a real y-intercept, following CCSS 8.EE.B.6.
The ball is the intercept: every pass starts at x = 0, so the ball's position is (0, b) and a wrong intercept is caught right away.
Real life: a constant rate with a starting amount is a linear equation, such as a taxi fare, a phone plan, or the grade of a ramp or road.
Levels of support: Easy previews the line as it is typed, Hard hides it, and there are 2-player and tournament modes.