1.2 Falling Balls

1.2 Falling Balls - Observations About Falling Balls • A...

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1 Phy 1405 1 Key Concepts: 1. Gravity 2. Mass and Weight 3. Projectile Motion Phy 1405 2 Observations About Falling Balls • A dropped ball: – Begins at rest, but soon acquires downward speed – Covers more and more distance each second • A tossed ball: – Rises to a certain height – Comes briefly to a stop – Begins to descend, much like a dropped ball • A thrown ball travels in an arc Phy 1405 3 Question 1 Why does a dropped ball fall downward? – What is gravity doing to the ball? Phy 1405 4 Gravity and Weight • Gravity exerts a force on the ball • That force is the ball’s weight • Since earth’s gravity produces the ball’s weight, that weight points toward the earth’s center • The ball’s weight causes it to accelerate toward the earth’s center (i.e., downward) Phy 1405 5 Clicker Question 2 Suppose that I throw a ball upward into the air. After the ball leaves my hand, is there any force pushing the ball upward? (A) Yes (B) No Phy 1405 6 Question 2 Do different balls fall at different rates? – If different balls have different weights and different masses, is there any relationship between their accelerations as they fall?
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2 Phy 1405 7 • A tennis ball and a golf ball dropped side-by-side in air. • The tennis ball is affected more by the air’s resistance than the golf ball. Demo Phy 1405 8 Weight and Mass • A ball’s weight is proportional to its mass weight/mass = constant • On earth’s surface, weight/mass = 9.8 newtons/kilogram – is the same for all balls (or other objects) – is called “acceleration due to gravity” Phy 1405 9 Acceleration Due to Gravity Why this strange name? weight/mass force/mass = acceleration Acceleration due to gravity, g, is an acceleration! g = 9.8 newtons/kilogram = 9.8 meter/second 2 g = 32 feet/second 2 On earth’s surface, all falling balls accelerate downward at 9.8 meter/second 2 (~10m/s 2 ) weight = mass · g ( F = m a ) Different balls fall at the same rate! Mass and weight are related.
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1.2 Falling Balls - Observations About Falling Balls • A...

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