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 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
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 5Add your direction (when solving for velocity only!)
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?
Calculating Speed
If you know any two of the variables, you can calculate the missing variable.
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
Determine the velocity of a football being thrown 75 meters in 5 seconds toward the east.
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?
a Fv Ivt
Math Practice. After 2.0s, Isabela was riding her bicycle at 3.0m/s on a straight path. After 5.0s, she was moving at 5.4m/s. What was her
acceleration?
Math Practice. After 3.0s, Mohammed was running at 1.2 m/s on a straight path. After 7.0s, he was running at 2.0m/s. What was his
acceleration?
Speed – Time Graphs
Shows how changes over time X axis = Y axis =
SPEEDTIME
SPEED
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
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