9-1: Describing Motion9-2: Speed & Velocity

When is an object in motion, and how can you calculate speed?

Anticipatory Set

How do you know when an object is in motion?

California StandardsScience Standard 8.1.a: Students know

position is defined in relation to some choice of a standard reference point and a set of reference directions.

Science Standard 8.1.b: Students know that average speed is the total distance traveled divided by the total time elapsed and that the speed of an object along the path traveled can vary.

California StandardsScience Standard 8.1.c: Students know how to solve problems involving distance, time, and average speed.Science Standard 8.1.d: Students know the velocity of an object must be described by specifying both the direction and the speed of the object.

Inputmotion: an object is in motion if its distance from

another object is changing.reference point: a place or object used for

comparison to determine if something is in motion.distance: the length of a path between two points.displacement: the length and direction that an

object has moved from it starting point.vector: a quantity that consists of both a magnitude

and a direction.

Inputspeed: the distance an object travels per unit of

time.average speed: divide the total distance traveled

by the total time.instantaneous speed: the rate at which an object

is moving at a given instant in time.velocity: speed in a given direction.slope: steepness of a line on a graph.

Input & ModelingRelative Motion

An object is in motion if it changes position relative to a reference point.

Whether or not an object is in motion depends on the reference point you choose.

Input & ModelingRelative Motion

Distance is the total length of the actual path between two points. Displacement is the length and direction of a straight line between starting and ending points.

Input & ModelingDistance & Displacement

Input & ModelingCalculating Speed

To calculate the speed of an object, divide the distance an object travels by the amount of time it takes to travel that distance

Speed = Distance

Time

Input & ModelingCalculating Speed

If a distance runner runs 10 miles in one hour, what is her speed.

Speed = Distance

Time

Speed = 10 miles = 10 mph (miles per hour)

1 hour

Input & ModelingCalculating Average Speed

To calculate average speed (v), divide the total distance traveled (d) by the total time (t).

Average Speed = Total Distance

Total Time

Input & ModelingCalculating Average Speed

A cyclist travels 32 kilometers during the first 2 hours. Then he travels 13 kilometers during the next hour. What is his average speed?

Average Speed = Total Distance

Total Time

v= 32 km + 13 km = 45 km

2 h + 1 h = 3 h

v= 15 km/h

Input & ModelingCalculating Velocity

Changes in velocity may be due to changes in speed, changes in direction, or both.Like displacement, velocity is a vector.It has magnitude and direction.

A jet airplane’s velocity could be described as 700 miles per hour to the east.

Input & ModelingGraphing Speed

The slope of a distance-versus-time graph represents speed, that is, the rate that distance changes in relation to time.Time is shown on the horizontal, or x-axis.Distance, or position, is shown on the vertical, or y-

axis.A point on the line represents the distance an

object has traveled from the origin or a reference point at a particular time.

Input & ModelingGraphing Motion

You can use distance-versus-time graphs to interpret motion.

HOMEWORK CONNECTION Read pages 338-347 in your Science textbook.

Complete the Section 9-1/9-2 Review & Reinforce

Write a detailed SUMMARY of the section and complete the UNANSWERED QUESTIONS section of your notes.

Choose two of the remaining Depth & Complexity ICONS in your notes and explain how they relate to this section.