Chapter 2Kinematics: Description of

Motion

Units of Chapter 2

Distance and Speed: Scalar Quantities

One-Dimensional Displacement and Velocity: Vector Quantities

Acceleration

Kinematic Equations (Constant Acceleration)

Free Fall

Position, Distance, Displacement

Position: Location that is described by referencing one object/person to another object/person.

Distance: Scalar quantity (magnitude only) that describes the length of the path traveled from beginning to end.

• A puppy runs 40 meters east and then does a 180 and runs 10 meters to the west, stops, and runs 10 more meters to the west.

• What was the puppy’s distance?

Position, Distance, Displacement

Displacement is a vector quantity that represents the distance from the starting point (initial, xo ) to the end( final, x) AND includes a direction.

Back to the Puppy

What was the Puppy’s displacement?

Speed

Average speed is a scalar rate that is equal to the distance traveled divided by the elapsed time:

Speed

At times an instantaneous speed is required. It is the speed measured over a very short time span. This is what a speedometer reads on your car or a radar gun on a police car reads.

Vector

A vector is a line that has both magnitude and direction. Manipulating vectors means defining a coordinate system, as shown in the diagrams to the left.

Velocity

Velocity is the rate the displacement changes in a unit of time. It is a vector quantity. Its unit is m/s.

If the puppy travels for 20 seconds, what was its average velocity?

Note

For motion in a straight line with no reversals, the average speed and the average velocity are the same.

If a Road Runner travels east 6 meters, and with a flying leap changes direction heads north for 8 meters, what was Road Runner’s speed and velocity if he covered the distance in 30 seconds?

Acceleration

Acceleration is the rate at which velocity changes.

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The units of acceleration are m/s/s or m/s2

It is a vector quantity