Level at Every Instant
A bullet fired horizontally at 400 m/s and a bullet dropped from the same height, at the same instant, hit level ground together, if air is ignored.
How can something moving at 400 m/s fall as fast as something at rest?
Page 1
Science · Honors Physics
Chapter 1: Kinematics with Calculus Readiness
Two independent motions sharing one clock.
A bullet fired horizontally at 400 m/s and a bullet dropped from the same height, at the same instant, hit level ground together, if air is ignored.
How can something moving at 400 m/s fall as fast as something at rest?
Make your guess to turn the page.
Still to come: 10 pages · Lab · Words to Know · What We Learned · 4 questions · Explain It in Writing · Open Questions
The idea this lesson is working on — Students believe the launch gives a projectile a force it carries with it, which fades as the ball slows. The book sets that against a lab where range equals horizontal velocity × time exactly, and against equal fall times for fired and dropped balls. Ask: what is touching the ball in flight? The idea to reach is that horizontal velocity persists because nothing removes it.
About the lab and the Galileo data — The lab launches from a 20 m platform with g = 9.8 m/s², so complementary angles do not tie there; that is used as the model's limit. The folio 116v numbers are Stillman Drake's reading of Galileo's notes (1973); the predictions shown are computed here from the first row, and Galileo's own figures differ slightly.