1. © 2010 Pearson Education, Inc. Chapter 4 Making Sense of the Universe: Understanding Motion, Energy, and Gravity

2. © 2010 Pearson Education, Inc. How do we describe motion? Precise definitions to describe motion: Speed: Rate at which object moves Example: 10 m/s Velocity: Speed and direction Example: 10 m/s, due east Acceleration: Any change in velocity units of speed/time (m/s 2 )

3. © 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/s 2 B.0 m/s 2 C.Impossible to calculate

4. © 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/s 2 B.0 m/s 2 C.Impossible to calculate

5. © 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/s 2 : speed increases 10 m/s with each second of falling.

6. © 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

7. © 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.

8. © 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.

9. © 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.

10. © 2010 Pearson Education, Inc. © 2014 Pearson Education, Inc. Clicker Question Which of the following does not have a net force? 1.A car coming to a stop 2.A bus speeding up 3.An elevator moving up at constant speed 4.A bicycle going around a curve 5.A moon orbiting Jupiter

11. © 2010 Pearson Education, Inc. © 2014 Pearson Education, Inc. Clicker Question Which of the following does not have a net force? 1.A car coming to a stop 2.A bus speeding up 3.An elevator moving up at constant speed 4.A bicycle going around a curve 5.A moon orbiting Jupiter