8.1 The Language of 8.1 The Language of MotionMotion

Some common words used to describe motion Some common words used to describe motion include:include:– DistanceDistance– Time Time – SpeedSpeed– PositionPosition

•How would you describe the motion of the soccer ball before and after it is kicked?•What key words did you use when describing this situation?

Direction Makes a Direction Makes a DifferenceDifference

Two main types of Two main types of quantities:quantities:– ScalarsScalars: Describe : Describe magnitude magnitude

but not directionbut not direction. (Magnitude . (Magnitude is the size of a measurement)is the size of a measurement) Example: Example: Johnny walked 25 kmJohnny walked 25 km

– VectorsVectors: Describe : Describe magnitude magnitude

and direction.and direction. Example: Example: Johnny walked 25 km Johnny walked 25 km

NorthNorth

Every time you use a map or give directions, you are using vectors.

Vectors vs. ScalarsVectors vs. Scalars

You can always tell if a quantity You can always tell if a quantity is a vector because there will be is a vector because there will be an arrow drawn above it.an arrow drawn above it.– Example:Example:

A scalar has no arrow.A scalar has no arrow.– Example:Example:

Northsmv /0.5

smv /0.5

Distance vs. DisplacementDistance vs. Displacement DistanceDistance ( (dd) is a ) is a scalar scalar that tells you how that tells you how

far something has travelled.far something has travelled.– Example: Example: Johnny ran a distance of 400 m

DisplacementDisplacement ( (dd) is a ) is a vectorvector that that describes your position relative to where describes your position relative to where you started.you started.– Example: Example: Johnny ran 400 m North of his home..

We can measure both We can measure both distancedistance and and displacementdisplacement in metres (m). in metres (m).

ExampleExample

A car leaves home and drives 10 km to the store and then returns home. The car has driven a total distance of 20 km but its final displacement is 0 km.

Time IntervalTime Interval Time interval or change in time is Time interval or change in time is

calculated by:calculated by:

Where: Where: ΔΔt = t = change in time change in time (the (the ΔΔ symbol is the greek letter symbol is the greek letter delta. delta. It It means “change”).means “change”).

tti i = = initial timeinitial time

ttf f = = final timefinal time

if ttt

The time interval to move from the fire hydrant to the sign is calculated by: s

sst

3

25

ExampleExample

DisplacementDisplacement Displacement or change in position is calculated by:Displacement or change in position is calculated by:

Where: = change in position or displacementWhere: = change in position or displacement

= initial position= initial position

= final position= final position

if d - d = dΔ

dΔ

fd

id

Displacement and DistanceDisplacement and Distance

Between 2 s and 5 s, the skateboarder’s:displacement is 5 m [E] and

distance travelled is 5 m.

Watch for SignsWatch for Signs

When using vector quantities, opposite directions are given opposite signs.

Copy the following diagram in your notes:Common Sign Conventions

Watch for SignsWatch for Signs

Consider the following situation:

…what is the person’s total displacement?….what about the total distance travelled?

Watch for SignsWatch for Signs

Between 0 s and 15 s the person’s displacement is:= 10 m [W] – 5 m [E] = -10 m – 5 m = -15 m = 15 m [W]

if d - d = dΔ

Watch for SignsWatch for Signs

Between 0 s and 15 s the total distance travelled is:= 15 m + 10 m + 20 m= 45 m

8.1 The Language of 8.1 The Language of MotionMotion

Time for some practice Time for some practice (homework):(homework):

#1-3 pg.147, and #1-3 pg.148-9 #1-3 pg.147, and #1-3 pg.148-9 in BC Science 10 workbookin BC Science 10 workbook

Uniform MotionUniform Motion

Uniform motionUniform motion is a term that is a term that describes objects that describes objects that do not speed do not speed up, slow down, or change directionup, slow down, or change direction. .

In other words, they In other words, they travel at travel at constant velocities constant velocities (we will discuss (we will discuss velocity more later)velocity more later)

ExampleExample

The position of the ball in this photo is shown at equal time intervals. How would you determine if this motion is uniform motion?

What would the picture look like if the ball was NOT in uniform motion?

More Examples…More Examples…

Graphing Uniform MotionGraphing Uniform Motion Motion of an object Motion of an object

can be analyzed by can be analyzed by drawing a position-drawing a position-time graphtime graph..

A position-time A position-time graph plots graph plots position position data on the vertical data on the vertical axis axis (y-axis) and (y-axis) and time data time data on the on the horizontal axis (x-horizontal axis (x-axis).axis).

Uniform Uniform motion is motion is represented represented by a by a straight straight lineline on a on a position-time position-time graph.graph.

Positive SlopePositive Slope

Slants Slants up to the up to the rightright..

Indicates an Indicates an object travelling object travelling in the in the positive positive direction direction (ie: (ie: North, East, to North, East, to the right, up, etc.)the right, up, etc.)

Zero SlopeZero Slope

Horizontal Horizontal lineline..

Indicates Indicates that the that the object is object is stationarystationary..

Negative SlopeNegative Slope

Slants Slants down to down to the rightthe right..

Indicates an Indicates an object travelling object travelling in the in the negative negative direction direction (ie: (ie: South, West, to South, West, to the left, down, the left, down, etc.)etc.)

8.1 The Language of 8.1 The Language of MotionMotion

Time for some practice Time for some practice (homework):(homework):

#1-7 pg.150, and #1-11 pg.151-#1-7 pg.150, and #1-11 pg.151-2 in BC Science 10 workbook2 in BC Science 10 workbook