Falling Objects

Free Fall Acceleration

Freely falling bodies undergo constant acceleration

• If air resistance is disregarded, all objects dropped near the surface of a planet fall with the same constant acceleration.

• This acceleration is due to gravitational force and is known as free fall.

• On Earth, ag has a magnitude of -9.81 m/s2 or -32 ft/s2. (It is negative because it directed downward toward earth.)

•pg56 Physics Serway /Faugh (Holt)

• This visualization of a gravity model was created with data from NASA's Gravity Recovery and Climate Experiment (GRACE) and shows variations in Earth’s gravity field.

• Gravity is determined by mass. Earth’s mass is not distributed equally, and it also changes over time.

• The colors in this image represent the gravity anomalies measured by GRACE. One can define standard gravity as the value of gravity for a perfectly smooth 'idealized' Earth, and the gravity 'anomaly' is a measure of how actual gravity deviates from this standard. Red shows the areas where gravity is stronger than the smooth, standard value, and blue reveals areas where gravity is weaker.

GRAVITY IS NOT EXACTLY THE SAME AT ALL EARTH LOCATIONS

Weak Strong

Different Planets = Different free fall rates of acceleration

• 0n August 2, 1971, a demonstration was conducted on the moon by astronaut David Scott. He simultaneously released a hammer and a feather from the same height above the moon’s surface. They both fell straight down and landed on the lunar surface at exactly the same moment. (ag on the moon = -1.62 m/s2 compared to Earth’s -9.81m/s2 •pg56 Physics Serway /Faugh (Holt)

When there is no air resistance, all objects fall with the same acceleration regardless of their masses.

•pg56 Physics Serway /Faugh (Holt)

The feather and the apple are released in a vacuum chamber. The two objects fell at exactly the same rate, as indicated by the horizontal alignment of the multiple images.

The pictures shows that even though the amount of time between pictures is equal, the displacement in each time interval did not.

Both the apple and the feather werein free fall and accelerated to Earthat the rate of 9.81m/s every second(-9.81m/s2).

Falling Ping Pong and Golf Balls

Distance Fallen = ½gt2 Notice the relationship between time, g and distance fallen. Distance increases proportionally with the square of the time

• Objects thrown into the air have a downward acceleration as soon as they are released.

• A soon as the ball is released, with an upward velocity of 10.5 m/s, it has ag = -9.81 m/s2.

• After 1s, the ball’s v is 0.69 m/s but ag is still -9.81 m/s2 (still moving

upward at this point) .

• After 2s, the ball’s v is 9.12 m/s and ag is still -9.81 m/s2 (moving

downward) .

The acceleration never changes throughout the ball’s travel (although the sign changes with direction).

Graph showing the velocity of the ball plotted against time.

WeightlessnessAstronauts on the International Space Station are weightless because when they are in Earth orbit they are in a continual state of free fall. Because they are traveling at such a high velocity, the Earth curves away beneath them.

Get out your 3D glasses to appreciate this

Weightless in a special aircraft known as the “vomit comet” that flies a parabolic path for a very short period of weightlessness.

Free-fall and Terminal Velocity If the Earth had no atmosphere, when

skydivers accelerate in free-fall, they would continue to accelerate to the ground, even if they could open their chutes (which would be difficult without an atmosphere).

Terminal velocity depends on an object’s mass, shape, and size.

A skydiver spread out typically has a terminal velocity of about 55 m/s (123 mph).

If the sky diver curls into a ball, terminal velocity may be close to 90 m/s (200 mph).

When the chute opens, and air resistance increases, the skydiver decelerates to a new slower terminal velocity – typically about 5m/s (11mph).

Felix Baumgarter – Highest (24 mi.) and Fastest Free Fall (1357.64 km/h (843.6 mph), or Mach 1.25)