Describing and Measuring Motion

Building Science Champions

In Thought Think of how you arrived to school today. Did

you walk, drive, take the bus? Write a paragraph describing how you got to school.

Great words to include in your paragraph:MotionSpeedAccelerationReference pointPosition

ObjectivesExplain when an object is in motion and how

motion is relative to a reference pointCalculate an object’s speed and velocity

using SI units of distanceGraph motion showing changes in distance as

a function of time

Key Terms MotionReference pointPositionMeterSpeedVelocity DisplacementSlope

Recognizing MotionHow would you describe an object in motionAn object is in motion when its distance from

another object is changingTo determine if something is in motion you need a

reference pointIf an object is moving at the same rate of speed as

you the object does not appear to be movingThe walls in your classroom do not appear to be

moving because they are moving at the same rate of speed as you

Earth is moving at 30 km per second – LA to NY is 2 min

Reference PointReference point is a place or object used for

comparison to determine if something is in motion

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

Position is an object’s distance and direction from a reference point

Using Reference Points At a school you may describe your position

compared to a hallway – ie “I am standing outside the 800’s.”

Direction is often used with a reference point “I am a block east of the train station.”

Reference point

Reference Point

Reference PointWhich one is in motion? How can you tell?

Can the other 2 be in motion?

Using Reference Points Describe the location of the yellow car from our vantage point.

Above the asphalt

To the right of the lead car.

To the left of the Texaco and Home Depot cars.

Describing Distance International System of Units (SI system)The basic SI unit of length is the meter

(metre)Meter is roughly 39 inchesDistance is how far two objects are from one

anotherSmaller Units of Distance

Larger Units of Distance

Deci = 1/10 of a meter Deka = 10 meters

Centi = 1/100 of a meter

Hecto = 100 meters

Milli = 1/1000 of a meter

Kilo = 1000 meters

Calculating SpeedSpeed of an object is the distance the object

travels in one unit of timeSpeed is a rate A rate tells you the amount of something that

occurs or changes in one unit of timeSpeed = unit of distance / unit of time

SPEED = DISTANCE / TIMEUsually speed is measured in m/s or km/h

Types of Speed Constant speed – is the rate of change in which

the same distance is traveled each second Instantaneous speed – is speed at a given instant

of timeAverage speed – is the total distance traveled

divided by the total time taken to travel that distance

v= d/t v equals average velocity d equals distancet equals time

What type of speed is shown in each picture?

Instantaneous Speed

Cruise Control

Constant Speed

Time from

Pt A to Pt B

Average Speed

Speed at this point

Instantaneous speed

Describing Velocity Velocity – speed in a given direction

35 meters per hour west

DisplacementDisplacement (s) – is the shortest distance

between two places/objectsShortest distance is a straight line s = final position of a point – the initial

position of a pointDisplacement formula s = Rf – Ri = ΔR

A

B

Graphing Motion On a line graph plot distance against timeTime is placed on the horizontal or x-axisDistance is placed on the vertical or y-axisSlope is the steepness, or slant, of a line on a

graph

ReviewSpeed is distance divided by timeVarious speeds include constant,

instantaneous and average speedUse a reference point to determine motionVelocity is speed in a given direction

ReferencesAnderson, M. et all (2012) Physical Science.

McGraw-Hill: ColumbusFrank, D.V et al (2001). Physical Science.

Prentice Hall: New Jersey