Physics Core/AP 1 and 2

Homework

# Physics Chapter 5: 4-7 Gravity and Weight

## Homework

Text Reading: Giancoli, Physics - Principles with Applications, Chapter 5: 4-8

##### Study Points
• 5. 4: It is possible for tangential velocity to be changing -- consider the ferris wheel as it slows down to let off passengers. We have two acceleration components in this case: one radial (as is required to keep the object moving in a circle), and one tangential (to control the speed of the rim). These are at right angles, so they can be analyzed separately and added as we add any x-y vector components. For the most part, we will not be concerned with situations where the object is changing tangential speed (v), in which case atan = 0, so a = atan + aR = aR. Centrifuges use the differential force applied to objects with different masses moving in a circle to separate out components of solutions.
• 5.5 Universal gravitation describes the basic property of all matter to attract all other matter with a force dependent only on the masses involved and their distance apart. The force of gravity is a mutual attraction. so the force between the earth and the apple is the same whether we talk about the earth's attraction for the apple or the apple's attraction for the earth.
• 5.6 Near the earth's surface, we can calculate the acceleration due to gravity g = GME/RE2 where ME is the mass of the earth and RE its radius (usually taken as "sea level"]. g = 9.77 m/sec2 or about 9.8 m/sec2.
• 5.7 Objects in orbit are in free fall. Since there is no normal force reacting to them, they do not feel weight. Restrained fall occurs when some object (the floor of the elevator, for example) keeps you from falling at the rate gravitational acceleration alone would provide. So close-orbit free fall does not mean the object is without weight, only that it experiences no normal force. Objects far enough from large masses undergo net zero gravitational forces, which is considered "real" weightlessness.

### Key Equations

Universal Gravitation:

Gravity and Circular motion where m1 is orbiting m2:

### Web Lecture

Read the following weblecture before chat: Universal Gravitation

### Study Activity

Use the gravity force lab to get a sense for how the attraction for each object changes when its mass increases or decreases.

### Chat Preparation Activities

• Forum question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
• Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

### Chapter Quiz

• The chapter quiz is not yet due.

### Lab Work

If you want lab credit for this course, you must complete at least 12 labs (honors course) or 18 labs (AP students). One or more lab exercises are posted for each chapter as part of the homework assignment. We will be reviewing lab work at regular intervals, so do not get behind!