Kinematics, uniform motion

Objectives
At the end of the lesson you will be able to
Define distance and displacement, speed and velocity,
describe uniform motion and graphical data
define operationally, compare and contrast scalar and vector quantities

Kinematics
Words to learn: Origin, Position, Scalar Quantity, Vector Quantity, Distance, Displacement, vector, magnitude, instantaneous speed.
Scalar and Vectors
Scalars are quantities that are fully described by a magnitude (or numerical value) alone.
Vectors are quantities that are fully described by both a magnitude and a direction.
The science of motion and its causes is called Mechanics, which
is divided into two main sections: Kinematics which describes motion
and Dynamics which describes the causes of motion.

POSITION, DISPLACEMENT AND DISTANCE
origin: a reference point
position: the straight-line
distance between the origin and
an object’s location; includes
magnitude and direction
"The treasure is hidden 25 paces (steps) northeast of the old hut"
This change in the position of an object is called the displacement

If a person walks 40 meters East, 10 meters South, 40 meters West, and finally 10 meters North.
The distance he covered is 100 m.
His displacement is 0 m

Distance vs Displacement

The Language of Motion
If you move from a position 5.0 m [W] to a position 10.0 m [E], what is your final distance and displacement?
East, north, up, and right are usually designated as positive.

Example 2
What is the distance covered and what was his displacement?

Position-time Graphs and Uniform Motion
The magnitude of the velocity vector is called speed which is a scalar quantity.
This golf ball is said to move with a constant velocity which is defined
as the displacement per unit time

Example
Determine the velocity of each object whose motion is represented by the graphs below.

Example 1
If a person walks 40 meters East, 10 meters South, 40 meters West, and finally 10 meters North. He completed his walk in 4 minutes. What was his speed? What was his velocity?

Example 2
What is the skiers average speed and average velocity?

Ex. 1
A thief snatches a handbag and runs north at 5.0 m/s. A police officer, 20 m to the south, sees the event and gives chase. If the officer is a good sprinter, going 7.5 m/s, how far will she have to run to catch the thief?
Ex.2
Two friends start walking on a football field in the same direction. Person A walks twice as fast as person B. However, person B has a head start of 20.0 m. If person A walks at 3.0 m/s, find the distance between the two friends after walking for 20.0 s and determine who is ahead at this time. Sketch a position-time graph for both people.
Ex.3
A mosquito flies toward you with a velocity of 2.4 km/h [E]. If a distance of 35.0 m separates you and the mosquito initially, at what point (distance and time) will the mosquito hit your sunglasses if you are travelling toward the mosquito with a speed of 2.0 m/s and the mosquito is travelling in a straight path?

Uniform Motion
Uniform = “Constant”
Neither the speed nor direction can change.
Direction: must be moving in a straight line, forward or back OR up or down.
Speed: can not be speeding up or slowing down.

1.4 Analyzing Velocity-time Graphs

Pg 38

Pg 42

Position as a Function of Time