Kawameeh 8th Grade Science

Chapter 1 – Lesson 1

How do you know when something is moving?

Reference Point - The starting point you chose to describe the location, or position of an object.

• Position - An object’s distance and direction from a reference point.

• A complete description of your position includes:

1. A distance2. A direction 3. A reference points

A flagpole can be used as a reference point for finding a bicycle at a school.

Practice Test Question

Practice Test Answer

Practice Test Question

Practice Test Answer

Measuring: Indicate which reference point is further. Use a ruler. (page 10)

How does the description of an object’s position depend on a reference point?

An object’s position is its in a certain from a reference point.

• Suppose your reference point changes…

The description of the position will because the reference point is different, however the actual position change at all.

distancedirection

change

will not

Reference Direction

Sometimes the terms and are used to determine reference direction.

positive negative

Describing the Reference Direction

A plus sign ( + ) indicates movement

A minus sign ( - ) indicates movement

in the direction of the reference point.

in the direction opposite of the reference point.

If the reference direction is EAST•Anything moving in the direction toward the

EAST would be • Anything moving in the opposite direction

would be

POSITIVE

NEGATIVE

Position as a Vector

A vector is a quantity in which two things must be specified:

1. Distance from the reference point2. Direction from the reference point

Dimensions and Reference Points

A dimension is when distance or length is measured in direction.

• If you were to describe a position in two directions you would be using

one

two dimensions

How would you describe your position?

Reference Directions in two dimensions:

•North•South

•East•West

•Forward

•Backward

•Up

•Down

•Left

•Right

Changes in position due to motion

Motion - the process of changing position.

How can you tell the boat moved?

What if the fishing pole was the reference point? What if the buoy was a reference point?

Distance vs Displacement

• Distance -

• Displacement -

the amount of space between two objects. The total length of the actual path from start to end.

the difference between the initial (first) position and the final position of an object. (straight line)

• When would distance and displacement be the same?• When an object moves in a straight line in

one direction.

Displacement

Direction of displacement is the direction from start point to end point

Size of displacement isthe distance from the starting point to the ending

point.

Distance and Displacement

Chapter 1 – Lesson 2

Speed, Velocity and Acceleration

Speed, velocity and acceleration describe how an objects position and motion change through time.

Rates measure change in something over a length of time.

What is speed?

Speed - A measure of the distance an object travels per unit of time.

How could we increase an objects speed?

• Move ~3 seconds for a distance of ~3meters• Move ~3 seconds for a distance of ~7meters

• Move ~5 meters in ~5 seconds• Move ~5 meters in ~2 seconds

Increasing an object’s speed

•By increasing the distance the object travels in the same time.

Or

•By decreasing the time it takes for an object to travel the same distance.

Calculating Speed

Speed (S) = distance object travels time it takes to travel distance

Measuring Unit Abbreviation

Distance meter mDistance kilometer kmTime seconds sTime hours hr

S= d t

Calculating Speed

If you know any two of the variables, you can calculate the missing variable.

STEPS TO COMPLETING A FORMULA

STEP 1

STEP 2

STEP 3

STEP 4

Write the formula

Plug in the information that you are given

Solve the answer

Add your units

STEP 5 Add your direction

PRACTICE

Calculate the speed of a car going 80 meters in 20 seconds.

PRACTICE

A girl runs 25 meters in 10 seconds. What is her speed?

Constant Speed

The rate of change of position in which the same distance is traveled each second.

•What distance has the car traveled at 2s?•How long will it take the car to travel 132m?

Average Speed

Average speed = total distancetotal time traveled

S= td tt

Solve the average speed: Melissa shot a model rocket 360 m into the air. It took the rocket 4s to fly that far. What was

the average speed of the rocket?

If Jessica ran 5 meters the first second, eight meters the next second, and 8 meters the third second to her house. What was

her average speed?

Instantaneous Speed

Speed at a specific instant in time.

When driving in a car you often change speed. What object in the car tells you

your instantaneous speed?

Speedometer

Velocity The speed and direction of a moving object.

How is velocity represented?

• The length of the arrow indicates the objects • A greater speed is shown by

SPEEDA LONGER ARROW

• The arrow should point in the direction of THE OBJECTSMOTION

Is their velocity the same?

NO – they are both walking the same speed because the arrow’s are the same length, however their

direction is different therefore the velocity is NOT the same

In what ways can your velocity change?

3. When BOTH the speed and direction change

1. When speed of an object changes2. When direction that the object moves changes

Chapter 1 – Lesson 3

A measure of the change in velocity during a period of time.

3. Change in direction (EVEN IF AN OBJECT IS TRAVELING AT A CONSTANT SPEED)

AccelerationAn object accelerates when its velocity changes as a result of:

1. Increasing speed

2. Decreasing speed

Are the horses in the carousel accelerating even though their speed is constant?

Calculating Acceleration

A bicyclist started from rest along a straight path. After 5s, his speed was 8m/s. What was his

acceleration during the time?

Speed – Time Graphs

Shows how changes over time X axis = Y axis =

SPEEDTIMESPEED

Object at Rest

• The speed is zero and does not change

• Horizontal line (like adistance – time graph y = 0 )

Constant Speed

• The line will be HORIZONTAL

•The further the line is from the the it is moving.

X - AXIS FASTER SPEED

Speeding Up

•The line on a speed – time graph is to the x-axis in the of thetime period when it has a speed.

•The line slants toward theright side of the graph as the speed .

CLOSERBEGINNING

LOWER

UPWARD

INCREASES

Slowing Down

•When initially starting to slow down the point representing speed is from the x-axis.

• As speed the points representing speed get to the x-axis.

•The line on a speed-time graph slopes to the right.

•When the line touches the x-axis, thespeed is and the objectstopped.

FAR

DECREASESCLOSER

DOWNWARD

ZERO

Comparing Distance – Time and Speed – Time Graphs

Objects at Rest

Comparing Distance – Time and Speed – Time Graphs

Constant Speed

Comparing Distance – Time and Speed – Time Graphs

Speeding Up

Comparing Distance – Time and Speed – Time Graphs

Slowing Down