Chapter 3 - MotionChapter 3 - Motion

Unit ObjectivesUnit ObjectivesDistinguish between distance and displacement.Distinguish between distance and displacement.

Calculate the average speed of an object.Calculate the average speed of an object.

Explain the difference between speed and velocity.Explain the difference between speed and velocity.

Write equations for the displacement and velocity of an Write equations for the displacement and velocity of an object over time.object over time.

Recognize and draw graphs of an objects displacement and Recognize and draw graphs of an objects displacement and velocity verses time.velocity verses time.

Describe how acceleration, time and velocity are related.Describe how acceleration, time and velocity are related.

Explain how positive and negative acceleration affect Explain how positive and negative acceleration affect motion.motion.

Interpret motion diagramsInterpret motion diagrams

Explain how forces and motion are related.Explain how forces and motion are related.

Compare and contrast static friction and sliding friction.Compare and contrast static friction and sliding friction.

Describe the effects of air resistance on falling objects.Describe the effects of air resistance on falling objects.

3.1 Notes - Motion3.1 Notes - Motion

Today’s ObjectivesToday’s Objectives

Distinguish between distance and Distinguish between distance and displacement.displacement.

Physics of MotionPhysics of Motion

Mechanics = the study of the motion Mechanics = the study of the motion of objects (physics of motion)of objects (physics of motion)

Kinematics = the science of Kinematics = the science of describing the motion of objects describing the motion of objects using words, diagrams, numbers, using words, diagrams, numbers, graphs and equations.graphs and equations.– Used to develop models that describe Used to develop models that describe

the motion of real-world objectsthe motion of real-world objects

New VocabularyNew Vocabulary

Scalar quantity = Scalar quantity = fully described fully described by a magnitude (or numerical value) by a magnitude (or numerical value) alone.alone.

Vector quantity = Vector quantity = fully described fully described by both a magnitude and a direction.by both a magnitude and a direction.

ExamplesExamples

Quantity Category

a. 5 m

b. 30 m/sec, East

c. 5 mi., North

d. 20 degrees Celsius

e. 256 bytes

f. 4000 Calories

Scalar

Scalar

Scalar

Scalar

Vector

Vector

MotionMotion

Occurs when an object changes Occurs when an object changes positionposition

Position depends on a reference Position depends on a reference frameframe– A reference point is chosen within the frame A reference point is chosen within the frame

and the position of the object is the distance and the position of the object is the distance and direction of the object from the reference and direction of the object from the reference pointpoint

– relative to a chosen reference framerelative to a chosen reference frame

DistanceDistance

The length of the path the object The length of the path the object travelstravels– Scalar quantityScalar quantity– Physical qualityPhysical quality– Does not have directionDoes not have direction– Not a vectorNot a vector– refers to "how much ground an object refers to "how much ground an object

has covered" during its motion.has covered" during its motion.

DisplacementDisplacement

Distance & direction of an objectDistance & direction of an object’’s s final position from its originalfinal position from its original– Size & DirectionSize & Direction– A VectorA Vector– refers to "how far out of place an object refers to "how far out of place an object

is" is" – it is the object's overall change in it is the object's overall change in

position.position.

Distance vs. DisplacementDistance vs. Displacement

ExampleExampleA physics teacher A physics teacher walks 4 meters East, 2 walks 4 meters East, 2 meters South, 4 meters South, 4 meters West, and meters West, and finally 2 meters North.finally 2 meters North.

Total Distance = _____Total Displacement = _____

12 m

0 m

Example 2Example 2

The position of a cross-country skier at various The position of a cross-country skier at various times. times.

At each of the indicated times, the skier turns At each of the indicated times, the skier turns around and reverses the direction of travel. around and reverses the direction of travel.

In other words, the skier moves from A to B to C to In other words, the skier moves from A to B to C to D.D.

Total Distance = _____Total Displacement = _____

420 m

140 m, right

Example 3Example 3

As a final example, consider a football coach As a final example, consider a football coach pacing back and forth along the sidelines. pacing back and forth along the sidelines.

The diagram below shows several of coach's The diagram below shows several of coach's positions at various times. At each marked positions at various times. At each marked position, the coach makes a "U-turn" and moves in position, the coach makes a "U-turn" and moves in the opposite direction. the opposite direction. – In other words, the coach moves from position A to B to C to D.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/homeworkIn-Class assignment/homework