Unit 2 Linear Motion - dentonisd.org is relative When we describe something in motion, we are comparing it to something else. For example: A car is driving 45 miles per hour: You only

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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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

time (s)

po

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(m

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