When we talk about how objects move in a straight line, we look at a few important ideas:

1. Position: This is called $x$. It tells us where an object is located compared to a starting point.

2. Displacement: This is written as $\Delta x = x_f - x_i$. It shows how much the position of an object has changed over time.

3. Velocity: We calculate this as $v = \frac{\Delta x}{\Delta t}$. We measure it in meters per second (m/s). Velocity tells us how fast something is moving and in what direction.

4. Acceleration: This is shown as $a = \frac{\Delta v}{\Delta t}$. It measures how quickly the velocity of an object changes. We usually express it in meters per second squared (m/s²).

These concepts help us understand and study linear motion, which means movement in a straight line. They also help us make predictions about how objects will move.