An Introduction to Acceleration: More Practice

Gravity and Free-Fall: Student Learning Goals Students will conduct an inquiry to measure gravitational acceleration, and calculate the percentage error of their experimental value (B2.3, B2.10)

Gravity and Free-Fall SPH4C

g The acceleration due to the Earth’s gravity is 9.8 m/s 2 [down]. The magnitude of this acceleration is denoted by the letter g.

Up, then Down An object feels this acceleration when travelling up (when it slows them down) and when travelling down (when it speeds them up).

Mass doesn’t matter Note that all objects, regardless of mass, experience the same acceleration.

Galileo This discovery is attributed to Galileo. yAfk

Drag However, some objects are slowed by atmospheric drag more than others.

Terminal velocity At a given speed, the drag will equal the gravity, and the object will stop accelerating, i.e. reach “terminal velocity.”

Terminal velocities Typical terminal velocities: Human53 m/s (190 km/h) Human with parachute5 m/s (18 km/h) Dandelion seed0.5 m/s (1.8 km/h)

The fastest man On August 16th, 1960 U.S. Air Force Captain Joe Kittinger broke the sound barrier (1240 km/h) during a free-fall from the high altitude balloon Excelsior III, at an altitude of approximately 31 km.

Highest fall survived (without a parachute) Flight attendant Vesna Vulovič fell 10,000 m on January 26, 1972 when she was aboard a plane that was brought down by explosives over the Czech Republic. She suffered a broken skull, three broken vertebrae (one crushed completely), and was in a coma for 27 days, but she survived!

g’s Accelerations are often given in terms of g. For example,

Blackout A typical person can handle about 5 g before loss of consciousness, “blackout,” occurs. The record for the most g forces on a roller coaster belongs to Mindbender at Galaxyland Amusement Park in Edmonton, Alberta, at 5.2 g.

Greyout Through the combination of special g- suits and efforts to strain muscles — both of force blood back into the brain— modern pilots can typically handle 9 g or more. They may experience a “greyout” (temporary loss of colour vision, tunnel vision, or an inability to interpret verbal commands) between 6 and 9 g.

Negative g’s Resistance to "negative" or upward g’s, which drive blood to the head, is much less (typically in the -2 to -3 g range). During “redout,” vision goes red, probably due to capillaries in the eyes bursting under the increased blood pressure.

“g -Force ” Acceleration perpendicular to the spine is more tolerable. Acceleration pushing the body backwards (“eyeballs in”) is tolerable up to 17g, and pushing the body forwards (“eyeballs out”) up to 12g.

Strongest g-forces survived Voluntarily: Colonel John Stapp in 1954 sustained 46.2 g in a rocket sled, while conducting research on the effects of human deceleration

Strongest g-forces survived Involuntarily: Formula One racing car driver David Purley survived an estimated 178 g in 1977 when he decelerated from 173 km/h to 0 in a distance of 66 cm after his throttle got stuck wide open and he hit a wall

Everyday g-forces Coughing: 3.5 g Sneezing: 2.9 g

Free fall Objects in free-fall feel 0 g, or “weightlessness.”