1. 4.7 Uniform Circular Motion
A particle is in uniform circular motion if it moves on a circular path of radius r with constant speed v.
Even though the speed is constant, the velocity is not. The reason is that the direction of the velocity vector changes from point to point along the path.
The fact that the velocity changes means that the acceleration is not zero.
The acceleration in uniform circular motion has the following characteristics:
Its vector points toward the center C of the circular path, thus the name “centripetal.”
Its magnitude a is given by the equation:
The time T it takes to complete a full revolution is known as the “period.” It is given by the equation:

2. Problem 59, Page 82
A woman rides a carnival Ferris wheel at radius 18 m, completing 4.6 turns about its horizontal axis every minute. What are (a) the period of the motion, and the magnitude of her centripetal acceleration at (b) the highest point and (c) the lowest point?

3. 4.8 Relative Motion in One Dimension
Suppose you see ducks flying north at 30 km/h.
Q1: What is the velocity of a duck as you see it?
Q2: What is the velocity of that duck as seen by another duck flying alongside?
The velocity of a particle depends on the reference frame of whoever is observing or measuring the velocity.
The above equation is read: “The coordinate of P as measured by A is equal to the coordinate of P as measured by B plus the coordinate of B as measured by A.” Note how this reading is supported by the sequence of the subscripts.

4. 4.9 Relative Motion in Two Dimensions
P 77: Snow is falling vertically at a constant speed of 8.0 m/s. At what angle from the vertical do the snowflakes appear to be falling as viewed by the driver of a car traveling on a straight, level road with a speed of 50 km/h?