Chapter 3 - Motion

Unit Objectives Distinguish between distance and displacement. Calculate the average speed of an object. Explain the difference between speed and velocity. Write equations for the displacement and velocity of an object over time. Recognize and draw graphs of an objects displacement and velocity verses time. Describe how acceleration, time and velocity are related. Explain how positive and negative acceleration affect motion. Interpret motion diagrams Explain how forces and motion are related. Compare and contrast static friction and sliding friction. Describe the effects of air resistance on falling objects.

3.1 Notes - Motion

Today’s Objectives Distinguish between distance and displacement.

Physics of Motion Mechanics = the study of the motion of objects (physics of motion) Kinematics = the science of describing the motion of objects using words, diagrams, numbers, graphs and equations. –Used to develop models that describe the motion of real-world objects

New Vocabulary Scalar quantity = fully described by a magnitude (or numerical value) alone. Vector quantity = fully described by both a magnitude and a direction.

Examples QuantityCategory a. 5 m b. 30 m/sec, East c. 5 mi., North d. 20 degrees Celsius e. 256 bytes f Calories Scalar Vector

Motion Occurs when an object changes position Position depends on a reference frame –A reference point is chosen within the frame and the position of the object is the distance and direction of the object from the reference point –relative to a chosen reference frame

Distance The length of the path the object travels –Scalar quantity –Physical quality –Does not have direction –Not a vector –refers to "how much ground an object has covered" during its motion.

Displacement Distance & direction of an object ’ s final position from its original –Size & Direction –A Vector –refers to "how far out of place an object is" –it is the object's overall change in position.

Distance vs. Displacement

Example A physics teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North. Total Distance = _____ Total Displacement = _____ 12 m 0 m

Example 2 The position of a cross-country skier at various times. At each of the indicated times, the skier turns around and reverses the direction of travel. In other words, the skier moves from A to B to C to D. Total Distance = _____ Total Displacement = _____ 420 m 140 m, right

Example 3 As a final example, consider a football coach pacing back and forth along the sidelines. The diagram below shows several of coach's positions at various times. At each marked position, the coach makes a "U-turn" and moves in the opposite direction. –In other words, the coach moves from position A to B to C to D. Total Distance = _____ Total Displacement = _____ 95 yds 55 yds, left

In-Class assignment/homework