1. Falling Bodies

2. Free-Fall
The act of falling towards the ground solely under the influence of the gravitational pull of the planet (i.e. Earth)
Dependent on the mass and size of the planet
Varies across the planet
World-wide average for the acceleration due to gravity at/near the surface of Earth:
𝑔=9.81 𝑚· 𝑠 −2  =magnitude of acceleration

3. Practice Problem #1
A sandbag is hanging from the rafters of a theater m above the stage floor. If the ropes break and it drops,
How fast will it be moving the instant it hits the floor?
How much time will it take to reach the ground?

4. Practice Problem #2
A baseball player tossed a ball straight up into the air with an initial velocity of m·s-1.
What was the maximum height that it reached?
How much time was it in the air, assuming it was caught at the same height as it had been released?

5. Graphing free-fall
What would a graph of velocity with respect to time look like for the baseball in the previous question?

6. Turn and talk:
What is air resistance?

7. Turn and talk:
A ping-pong ball that has been filled with sand is dropped from a second-story window at the same time as an identical, although empty, ping-pong ball.
Which will experience more air resistance?
Which will hit the ground first?

8. Falling objects… WITHOUT air resistance
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WITH (and without) air resistance
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9. Air Resistance A force that results from collisions with air molecules
For falling objects, the air resistance is a force that pushes in a direction opposite the direction of motion and slows the rate of acceleration during the fall.
The magnitude of air resistance depends on 2 things:
The surface area of the falling object
The speed of the falling object

10. Graphing air resistance
Sketch your prediction of a velocity- time graph for a falling object when air resistance is non-negligible.

11. Effects of Air Resistance on Falling Bodies
Acceleration experienced by the object in free-fall has changed
Greater surface area = greater number of collisions = larger magnitude of force of air resistance
Faster speed = greater number of collisions = larger magnitude of force of air resistance
EFFECTS of air resistance depend on the magnitude of the force and the mass of the object

12. Warm-up
Assume air resistance is negligible:
Eileen is in a hot-air balloon and is rising vertically at a speed of 11.7 m·s-1. She was m above the ground when she accidentally dropped a bag of apples.
How fast was the bag of apples going the instant it hits the ground?
How much time does it take to reach the ground?
What is the bag’s maximum height above the ground?