Physics 01
How Fast Does a Skydiver Fall? Belly, Head Down, Canopy
Belly down a skydiver tops out near 55 m/s (200 km/h), head down near 75 m/s, under canopy about 5 m/s. Here is the drag math and a jump timeline.
simulations
Physics 02
Why Does a Steel Ship Float but a Steel Ball Sinks?
Steel is 7.9 times denser than water, yet a ship with 10,000 t of cargo floats 5.6 m deep. Archimedes' principle, worked out for ships, icebergs, eggs and the Dead Sea.
Physics 03
Why Does an Ambulance Siren Change Pitch as It Passes?
At 90 km/h a 700 Hz siren is heard at 755 Hz coming and 652 Hz going, 2.5 semitones apart. Here is the Doppler math, and how to read speed from the pitch.