Unit 2 Linear Motion
Unit 2
Linear Motion
Kinematics
Kinematics is the study of howthings move, but does not address the question of why they move.
Dynamics
The study of why things move is called dynamics.
Therefore, the “general” term for the study of motion (the how and why) is called: MECHANICS
Motion is relativeWhen we describe something
in motion, we are comparing it to something else.
For example:
A car is driving 45 miles per hour:
You only know it is moving because the road and trees around it are staying still.
So, for motion to be found, there must be something that is stationary---called a reference point
SpeedSpeed is a measure of how
fast something is moving.
The speed at any instant is called instantaneous speed.
Average speed = total distancetime interval
SPEED AND DISTANCE
When you measure speed, it is based on the “TOTAL” distance covered
OR, “how far” an object has traveled in a given amount of time
Graphs of Motion
You can graph the relationships of both distance and time by using x and y values.
X is independent and Y is dependent
GRAPHS FOR SPEED
Graph for constant speed---x axis is time in seconds; y axis is distance in meters-
Graph for variable speed ---also called changing speed
Direct relationship graph—X & Y do the same thing.
Graphs of Motion
As you graph the relationships of both time and distance, so can speed and displacement (position) by using x and y values on a graph
Remember:
“per’ means “every”
So, 45 miles per hour is saying that something moves a distance of 45 miles EVERY hour
(distance/time)
What is the speed of a man running 8 miles in 2 hours?
Answer:
8 miles (total distance) / 2 hours (time interval)
8/2 = 4 miles/hour
Velocity
Velocity is speed in one direction.
Constant velocity IS remaining the same, or CONSTANT.
Changing velocity is NOT remaining the same, or CHANGING.
TERMS RELATED TO MOTION
Displacement: change in position due to a “difference” in start position and final position
Displacement is used with the term “velocity”
GRAPHS AND RELATIONS
Direct relationship graphs:
Straight line---x and y axis do the same thing (increase or decrease)
Inverse relationship---x and y axis do the “opposite” of each other ( i.e. x will increase and y will decrease)
VELOCITY AND DISPLACEMENT
Velocity is a “vector” quantity, therefore it has direction
The main difference between speed & velocity----velocity has direction and displacment
Velocity has displacement (position) which means that there is an “initial or start” point and a “final” point. So, df--final
or di—start or initial point
Graphs of Motion
The slope of the line in a position (displacement) vstime graph is velocity.
Graphs for velocity
Velocity can be constant or it can be variable----see example of
Constant velocity
Variable velocity
Note the “y” axis
position vs time
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time (s)
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