Kinematics

What rules govern an objects motion?

Answer Me!!!

List three things that come to mind when you hear the term motion?

After creating your list, Think-Pair-Share with a neighbor to what motion is…

What is Motion?

Motion is the change in an object’s position over a period of time.

There are many forms of motion, this unit is devoted to Linear Motion – motion along a straight line or motion in one dimension.

Coordinate Systems

In order to measure motion, you must first have a frame of reference set up.

Most importantly, you must establish your “zero point” or origin.

Choosing the Origin

You can choose the origin of these problems to be anywhere you would like. So choose a point that will make calculations less complicated. Your calculator thanks you…

Displacement

Displacement (Δd) is the change in position of an object (ending position – starting position) for a specified period of time.

Distance is how far the object actually traveled through that period of time.

Final Thought…

What is the difference between distance and displacement?

A woman travels in an elevator from the 8th floor to the 2nd floor. What is her displacement?

I drove 5 km north stopped and then drove 1.5 km south. What is my distance traveled? What is my displacement?

Answer Me!!!

Sketch a graph of the information in the chart to the right.

Think about what this chart represents.

We will use this chart for today’s discussion.

Time (s) Position (m)

0 0

1 5

2 10

3 15

4 20

5 25

Position-Time GraphsPosition vs. Time

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1015202530

0 1 2 3 4 5 6

Time (s)

Pos

itio

n (m

)

Speed and Velocity

Velocity is the rate of change in an object’s position over time.

Velocity is an object’s speed with a direction.

Position-Time Graphs

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0 1 2 3 4 5 6

Time (s)

Pos

itio

n (m

)

Average Velocity and Velocity Average velocity occurs over a period of time and

can be calculated using:

Average velocity could also be calculated using the following formula:

Instantaneous velocity (v) happens at an exact moment in time and represents the actual velocity of the object.

tave

d

v

2

ifave

vvv

Final Thought…

Describe the motion show in the graph.

What is the average velocity of the object?

What is the maximum velocity of the object?

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-40

-30

-20

-10

0

10

20

30

40

50

0 1 2 3 4 5 6

Time (s)

Pos

itio

n (m

)

Answer Me!!!

What does it mean to accelerate?

Velocity-Time Graphs

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01020304050

0 1 2 3 4 5 6

Time (s)

Pos

itio

n (m

)V

eloc

ity

(m/s

)

Acceleration

Acceleration is the rate of change in an object’s velocity over time.

How much will an object’s speed change in one second.

Acceleration

Acceleration takes place over a time period and can be calculated using the equation:

a vt

v f v it

Final Thought…

If an object traveling at 20m/s comes to rest in 4 seconds. What is the objects acceleration?

Answer Me!!!

A ball is rolling down a hill at a speed of 3 m/s. As the ball rolls, it accelerates at .5 m/s2. How far will the ball roll in 10 seconds?

Head Problems

To answer kinematics questions with multiple steps, keep organized with the “Head Problems” chart:

vi vf v a d t

Answer Me…

Fill out the Head Problems chart for the following situation. A car traveling at 20 m/s skids to a stop over a distance of 100 meters. Find the acceleration of the vehicle and the stopping time.

Think-Pair-Share

A piece of paper and a text book are dropped from the ceiling of the classroom. Why do they fall? Which will hit the ground first? Explain your

thinking.

Acceleration Due to Gravity

The Earth’s gravitational pull causes objects to accelerate toward the ground at a rate of 9.81 m/s2.

Free Fall

Free fall is defined as the state of an object that is falling towards Earth’s surface with no other forces acting on that object.

All object’s in free fall have the same acceleration (9.81 m/s2)

Solving Free Fall Problems

Use the “head problems” method: Remember a is going to be 9.81 m/s2

vi vf v a d t

9.81m/s2

Practice Problem

A tennis ball is thrown straight up with an initial speed of 22.5 m/s. How high does the ball rise? How long will the ball take to reach the peak?

vi vf v a d t

9.81m/s2

Final Thought…

A ball is dropped from the top of a building lands after 10.2 seconds. What is the velocity of the ball when hitting the ground?