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Unformatted text preview: the big picture Putting Chapter 4 into Context Weve covered a lot of ground in this chapter, from the scientific terminol- ogy of motion to the overarching principles that govern motion throughout the universe. Be sure you understand the following big picture ideas: Understanding the universe requires understanding motion. Motion may seem complex, but it can be described simply using Newtons three laws of motion. Today, we know that Newtons laws of motion stem from deeper physical principles, including the laws of conservation of angular momentum and of energy. These principles enable us to understand a wide range of astronomical phenomena. Newton also discovered the universal law of gravitation, which ex- plains how gravity holds planets in their orbits and much morein- cluding how satellites can reach and stay in orbit, the nature of tides, and why the Moon rotates synchronously around Earth. Perhaps most important, Newtons discoveries showed that the same physical laws we observe on Earth apply throughout the universe. Chapter 4 Making Sense of the Universe 105 summary of key concepts 4.1 Describing Motion: Examples from Daily Life How do we describe motion? Speed is the rate at which an object is moving. Velocity is speed in a certain direction. Acceleration is a change in velocity, meaning a change in either speed or direction. Momentum is A force can change an objects momentum, causing it to accelerate. How is mass different from weight? An objects mass is the same no matter where it is located, but its weight varies with the strength of gravity or other forces acting on the object. An object becomes weightless when it is in free-fall , even though its mass is unchanged....
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- Spring '08