Kinematics The study of motion without regard to the forces that cause the motion

Motion Motion is all around us: In the everyday activities of people. Cars on the highway. Jets in the air. With patience, even the stars in the nighttime sky.

Motion There is motion at the microscopic level that we cannot see directly: Jostling atoms make heat or even sound. Vibrating electrons produce light. Flowing electrons make electricity.

Motion Is easy to recognize, but harder to describe. Even the Greek scientists of 2000 years ago, who had a very good understanding of the ideas of physics we study today, had great difficulty describing motion. They failed because they did not understand the idea of rate. A rate is a quantity divided by time.

Goal 2: Build an understanding of linear motion. Objectives – Be able to: 2.01 Analyze velocity as a rate of change of position:  Average velocity.  Instantaneous velocity Compare and contrast scalar and vector quantities:  Distance and displacement.  Speed and velocity.

Motion A rate tells how fast something happens, or how much something changes in a certain amount of time. In this unit, you will learn how motion is described by rates known as speed, velocity, and acceleration.

Motion is Relative Everything moves. Even things that appear to be at rest move. They move with respect to, or relative to, the sun and stars. A book that is at rest, relative to the table it lies on, is moving … … at about 30 kilometers per second relative to the sun … … and it moves even faster relative to the center of our galaxy.

Motion is Relative When we discuss the motion of something, we describe its motion relative to something else. When we say that a space shuttle moves at 8 kilometers per second, we mean relative to the earth below.

Motion is Relative When we say a racing car at the Daytona 500 reaches speeds of 275 kilometers per hour, of course we mean relative to the track. The most common frame of reference is the earth.

Displacement To describe the motion of an object, we must be able to specify the location of the object at all times. A coordinate system specifies the position.

Displacement Often, a cleverly chosen coordinate system simplifies the solution of many problems, because the choice of the frame of reference is arbitrary.

Displacement Displacement is an object’s change in position. It’s the vector that points from the object’s initial position to its final position, regardless of the path taken. Since displacement means change in position, it is generally denoted Δs, where Δ denotes change in and s indicates spatial location. (The letter p is not used because it’s reserved for another quantity, momentum.) If the dispacement is horizontal, use Δx. If the displacement is vertical, use Δy.

Displacement Initial position is indicated by the vector labeled x 0. The length of x 0 is drawn from some arbitrarily chosen reference point.

Displacement At a later time, the car has moved to a new position, denoted with the vector x. Δx = x - x 0 SI unit: meter (m)

Displacement Often, we’ll deal with motion in a straight line. In such a case, a displacement in one direction along a line is assigned a positive value, and a displacement in the opposite direction is assigned a negative value. Example: Assume a car is moving in an east/west direction and that a positive (+) sign is used to denote a direction due east. Then, Δx = +500 m represents a displacement that points to the east and has a magnitude of 500 m. If Δx = -500 m, the displacement is due west.

Displacement Example 1 A rock is thrown straight upward from the edge of a 30 m high cliff, rising 10 m, then falling all the way down to the base of the cliff. Find the rock’s displacement.

Displacement Example 2 An infant crawls 5 m east, then 3 m north, then 1 m east. Find the magnitude and direction of the infant’s displacement.

Displacement Example 3 In a track-and-field event, an athlete runs exactly once around an oval track, a total distance of 400 m. Find the runner’s displacement for the race.

Goal 2: Build an understanding of linear motion. Objectives – Be able to: 2.01 Analyze velocity as a rate of change of position:  Average velocity.  Instantaneous velocity Compare and contrast scalar and vector quantities:  Distance and displacement.  Speed and velocity.