Section 3 Falling Objects Chapter 2 Free Fall

Section 3 Falling Objects Chapter 2 Free Fall Free fall is the motion of a body when only the force due to gravity is acting on the body. The acceleration on an object in free fall is called the acceleration due to gravity, or free-fall acceleration. Free-fall acceleration is denoted with the symbols ag (generally) or g (on Earth’s surface).

Acceleration due to Gravity Near the surface of the Earth, all objects accelerate at the same rate (ignoring air resistance). This acceleration vector is the same on the way up, at the top, and on the way down! a = -g = -9.8 m/s2 9.8 m/s2

Graphs of a ball thrown straight up x The v graph has a slope of -9.8 m/s2. The acceleration of the ball is -9.8 m/s2 all the way through the “flight” t v t a t

Practice If I threw a ball vertically upward at an initial speed of 34.5 m/s, how many seconds would it take to reach its maximum height? If a rock fell down a cliff and hit the bottom of the ravine at 4.0 s, how fast was the rock going when it hit the bottom of the cliff? If a ball was thrown upward at 46.3 m/s, what would be its maximum height? How far would a skydiver fall during his first minute of free fall? How long would it take for a penny to fall from the top of the 381. m high Empire State Building?

1. A rocket moves upward, starting from rest with an acceleration of +29.4 m/s2 for 3.98 s. It runs out of fuel at the end of the 3.98 s but does not stop. How high does it rise above the ground? 2. A small fish is dropped by a pelican that is rising steadily at 0.50 m/s. After 2.5 s, what is the velocity of the fish? How far below the pelican is the fish after 2.5 s?