Day 72: "Equationless" Kinematics


You won’t see any big scary kinematics equations in my college-prep physics course. All motion problems are solved by analyzing velocity-time graphs. Everything is on that graph: time, initial and final velocity, displacement (area), and acceleration (slope). Using the graphs reinforces their meaning and interpretation (which kids struggle with, yet get short shrift in most texts which instead focus on x = vit + 1/2at2 and vf2 = vi2 + 2ax), and kids only need to use two concepts: area and slope.

The whiteboard above is the solution to the following:

A dog runs down his driveway with an initial speed of 5 m/s for 8 s, then uniformly increases his speed to 10 m/s in 5 s.
a. What was the dog’s acceleration during the 2nd part of the motion?
b. How long is the driveway?

You can read more about the graphs-only approach at Kelly O’Shea’s awesome blog post: Velocity Graphs into Equations




About Frank Noschese

HS Physics Teacher constantly questioning my teaching.

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