Understanding how things move in a straight line involves some important ideas about speed. Let’s break down these concepts:

1. Initial Velocity ($v_i$):

   • This is the speed at which an object starts moving.
   • It influences how long it takes the object to reach its final destination.

2. Final Velocity ($v_f$):

   • This is the speed of the object at the end of its journey.
   • It changes based on how fast the object speeds up or slows down (called acceleration) and the time it takes.

3. Kinematic Equations:

   • A simple equation to remember is:
     $v_f = v_i + at$
     In this equation, $a$ stands for acceleration, and $t$ is the time.

4. Gravity:

   • When things fall, they speed up at a rate of about $9.81 \, \text{m/s}^2$ because of gravity.
   • This affects their final speed based on the starting speed ($v_i$) and how long they fall ($t$).

Knowing about these elements helps us better predict how and when an object will move.