## Quick Reference

A graph that shows displacement plotted against time for a particle moving in a straight line. Let *x*(*t*) be the displacement of the particle at time *t*. The distance-time graph is the graph *y*=*x*(*t*), where the *t*-axis is horizontal and the *y*-axis is vertical with the positive direction upwards. The gradient at any point is equal to the velocity of the particle at that time. (Here a common convention has been followed, in which the unit vector **i** in the positive direction along the line has been suppressed. The displacement of the particle is in fact a vector quantity equal to *x*(*t*)**i**, and the velocity of the particle is a vector quantity equal to *x*(*t*)**i**.)

*Subjects:*
Mathematics.