# 1.2 Speed & Velocity Many people use the terms speed and velocity interchangeably in everyday language. However, they have very different meanings in.

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1.2 Speed & Velocity Many people use the terms speed and velocity interchangeably in everyday language. However, they have very different meanings in physics. Speed is defined as the distance travelled per unit time. Velocity is defined as the displacement (change in position) of an object per unit time. Uniform Motion is motion at a constant speed in a straight line. Non-Uniform Motion is motion that is not at a constant speed or in a straight line (accelerated motion).

1.2 Speed & Velocity Average Speed (𝒗) is the total distance travelled divided by the total time taken to travel that distance. It is a scalar quantity. SI units – metres per second (m/s). Average Velocity ( 𝒗 ) is the total displacement, or change in position, divided by the total time for that displacement. It is a vector quantity. SI units – metres per second (m/s). SP #2 p.14, SP #1,2 p.17-18

1.2 Position-Time Graphs A position-time graph ( 𝒅 ˗𝒕) is a graph that describes the motion of an object, with position on the (vertical) y-axis, and time on the (horizontal) x-axis. Recall from Grade 9 Math that the slope (m) of a line is a measure of its steepness.

1.2 Position-Time Graphs The slope of a position-time graph gives the velocity of the object. If an object is moving with a constant velocity it will produce a straight line on a 𝒅 ˗𝒕 graph . A straight line on a 𝒅 ˗𝒕 graph represents uniform motion. The steeper the slope, the higher the object’s velocity.

1.2 Position-Time Graphs Graph A
The graph is a horizontal straight line. The slope of the graph is zero; the object’s velocity is zero. The object is at rest at a positive position [East] relative to the reference point.

1.2 Position-Time Graphs Graph B
The graph is a horizontal straight line. The slope of the graph is zero; the object’s velocity is zero. The object is at rest at a negative position [West] relative to the reference point.

1.2 Position-Time Graphs Graph D
The graph is a straight line with a constant, positive slope. The object’s velocity is constant in the positive direction. From the y-axis, we can see that the cyclist is moving eastward.

1.2 Position-Time Graphs Graph E
The graph is a straight line with a constant, negative slope. The object’s velocity is constant in the negative direction. From the y-axis, we can see that the cyclist is moving westward.

1.2 Position-Time Graphs For segments A, B, C of the following position-time graph: Describe the object’s motion. Determine the object’s displacement & velocity .

1.2 Homework Questions #1-8 p.20

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