Teach Fzx Tuesday - Projectile Independence

Projectile motion is normally taught before the students know any physics.  They just have to believe what we tell them.  It's a bit dumb.

Since we did Newton's laws of motion before projectiles this year, projectile motion began with diagrams of net force and acceleration.

Then we moved to the resulting velocity diagrams.  They sketch - then we discuss.

All that so they can tell me that we must SEPARATE the horizontal and vertical components of velocity, displacement, and acceleration into two INDEPENDENT columns of information to solve these problems.  This is the solution template we use.

Only time can cross that line.  We find the components of velocity to start the problem, always remembering that vector components are vector replacements.

(We can put velocity components together at the end for the final velocity.)

When called to take a quiz to find landing position and final velocity, some solutions look like this:

And some correctly separate the problem into two sets of information and basically do it right.

No matter which way we do projectiles, the one thing must remember is that vertical and horizontal are INDEPENDENT of each other - like the UK and the US since 1776.