Transcript Ch 4 Feb 3
Chapter 4 Making Sense of the Universe: Understanding Motion, Energy, and Gravity © 2010 Pearson Education, Inc. How do we describe motion? Precise definitions to describe motion: • Speed: Rate at which object moves ö speed = distance æçèunits of m ÷ s ø time Example: 10 m/s • Velocity: Speed and direction Example: 10 m/s, due east • Acceleration: Any change in velocity units of speed/time (m/s2) © 2010 Pearson Education, Inc. Clicker Question If you are driving south along I 280 at a constant speed of 100 km/hr, your acceleration is __. A. 100 m/s2 B. 0 m/s2 C. Impossible to calculate © 2010 Pearson Education, Inc. Clicker Question If you are driving south along I 280 at a constant speed of 100 km/hr, your acceleration is __. A. 100 m/s2 B. 0 m/s2 C. Impossible to calculate © 2010 Pearson Education, Inc. The Acceleration of Gravity • All falling objects accelerate at the same rate (not counting friction of air resistance). • On Earth, g ≈ 10 m/s2: speed increases 10 m/s with each second of falling. © 2010 Pearson Education, Inc. The Acceleration of Gravity (g) • Galileo showed that g is the same for all falling objects, regardless of their mass. Apollo 15 demonstration © 2010 Pearson Education, Inc. Clicker Question In the previous movie, the hammer and feather fell at the same rate because ___. A. The moon has no gravity. B. The moon has no atmosphere. C. The moon’s gravity is the same as Earth’s gravity. © 2010 Pearson Education, Inc. Clicker Question In the previous movie, the hammer and feather fell at the same rate because ___. A. The moon has no gravity. B. The moon has no atmosphere. C. The moon’s gravity is the same as Earth’s gravity. © 2010 Pearson Education, Inc. Momentum and Force • Momentum = mass velocity • A net force changes momentum, which changes velocity, generally meaning an acceleration. • Rotational momentum of a spinning or orbiting object is known as angular momentum. © 2010 Pearson Education, Inc. Clicker Question Which of the following does not have a net force? 1. 2. 3. 4. 5. A car coming to a stop A bus speeding up An elevator moving up at constant speed A bicycle going around a curve A moon orbiting Jupiter © 2014 Pearson Education, © 2010 Pearson Education, Inc. Inc. Clicker Question Which of the following does not have a net force? 1. 2. 3. 4. 5. A car coming to a stop A bus speeding up An elevator moving up at constant speed A bicycle going around a curve A moon orbiting Jupiter © 2014 Pearson Education, © 2010 Pearson Education, Inc. Inc.