8.1 The Language of Motion Common words used to describe motion: Distance Time Speed Position 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 Difference Two main types of quantities: Scalars: Describe magnitude (size of a measurement) but not direction. Ex: Johnny walked 25 km Vectors: Describe magnitude & direction. Ex: Johnny walked 25 km North Every time you use a map or give directions, you are using vectors.

Vectors vs. Scalars A vector has an arrow drawn above it. Example: A scalar has no arrow.

Distance, Position, & Displacement Distance (d) is a scalar that tells you the length of the path between 2 points/locations Ex: Johnny ran a distance of 400 m Position ( d ) is a vector quantity that describes a specific point relative to a reference point. Ex: The school is 3.0 km east of my house. If an object moves from one position to another we say it experiences a displacement.

Displacement (d) is a vector that describes the straight line distance & direction from one point to another. Ex: Johnny ran 400 m North of his home. We measure distance, position, & displacement in metres (m). 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 Interval Time interval or change in time is calculated by: Where: Δt = change in time (the Δ symbol is the greek letter delta. It means “change”. ti = initial time tf = final time

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

Displacement Displacement or change in position is calculated by: Where: = change in position or displacement = initial position = final position

Displacement and Distance Between 2 s and 5 s, the skateboarder’s: displacement is 5 m [E] and distance travelled is 5 m.

Watch for Signs! When using vector quantities, opposite directions are given opposite signs. Common sign conventions 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] See page 349 (c) McGraw Hill Ryerson 2007

Uniform Motion a term that describes objects that do not speed up, slow down, or change direction Objects will travel equal displacements in equal time intervals In other words, they travel at constant velocities.

Graphing Uniform Motion Motion of an object can be analyzed by drawing a position-time graph. plots position data on the y-axis & time data on the x-axis Uniform motion is represented by a straight line

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

Zero Slope Horizontal line. Indicates that the object is stationary.

Negative Slope Slants down to the right. Indicates an object travelling in the negative direction (ie: South, West, to the left, down, etc.) Take the Section 8.1 Quiz