lesson 1 - now 1.you must use a reference point to describe an object’s motion. 2.an object that...
TRANSCRIPT
1. You must use a reference point to describe an object’s motion.
2. An object that is accelerating must be speeding up.
Do you agree or disagree?
• What information do you need to describe the motion of an object?
• How are speed, velocity, and acceleration related?
• How can a graph help you understand the motion of an object?
Describing Motion
• motion
• reference point
• distance
• displacement
Describing Motion
• speed
• velocity
• acceleration
• Motion is the process of changing position.
• The starting point you use to describe the motion or the position of an object is called the reference point.
• In addition to using a reference point to describe motion, you also need a direction.
Motion
Name three reference points in this picture you can use to describe the motion of the baseball.
• Distance is the total length of the path traveled.
• Displacement is the distance between an initial, or starting, position, and a final position.
Motion (cont.)
The distance traveled and the displacement from the game to the vending machine differ.
Motion (cont.)
Motion (cont.)
What information do you need to describe an object’s motion?
Motion (cont.)
What information do you need to describe an object’s motion?
Answer: you need a reference point, a direction, and a distance.
• Speed is the distance an object moves divided by the time it took to move that distance.
• Speed can be constant or changing.
• Average speed is the ratio of the distance an object moves to the time it takes for the object to move that distance.
Speed
Speed (cont.)
The girl moves with constant speed during the first 4 seconds. The girl’s speed begins to change between seconds 4 and 5.
Velocity is the speed and direction of an object’s motion.
What practical uses are their for velocity?
• Storm tracking
• Air and sea travel
Velocity
Often, velocity is shown by using an arrow. The length of the arrow represents the speed of an object, while the direction in which the arrow points represents the direction in which the object is moving.
Each segment of the arrow shows the distance and the direction you move in a given unit of time.
Because each segment is the same length, you are moving the same distance and in the same direction during each interval of time.
Because both your speed and direction of movement are constant, you are moving at a constant velocity.
The velocity of an object changes if the speed changes, the direction changes, or both the speed and the direction change.
• Because velocity includes both speed and direction, velocity can change if the speed of an object remains constant.
• When either an object’s speed or velocity changes, the object is accelerating.
• Acceleration is the measure of how quickly the velocity of an object changes.
Velocity (cont.)
Velocity (cont.)
An object moving at a constant speed can have a change in velocity. Explain how to your partner.
Velocity (cont.)
An object moving at a constant speed can have a change in velocity. Explain how to your partner.
Answer: because the direction of the object can change which would change the velocity of the object.
• Average acceleration can be calculated by using the following equation:
• This equation refers only to a change in speed, not direction.
• The symbol vf represents final velocity, vi represents initial velocity, and t represents time it takes to make that change in velocity.
Calculating Acceleration
• When an object speeds up, its final velocity is greater than its initial velocity.
• When an object speeds up, it has positive acceleration.
• When an object slows down, the initial velocity is greater than its final velocity.
• As an object slows down, it has negative acceleration, or deceleration.
Calculating Acceleration (cont.)
A displacement-time graph shows an object’s speed and distance from the reference point at any given time.
Using Graphs to Represent Motion
On a displacement-time graph, the x-axis shows the time and the y-axis shows the displacement from a reference point.
The line on a displacement-time graph represents the average speed of an object at a particular moment in time.
On a speed-time graph, the x-axis shows the time, and the y-axis shows the speed of an object.
The line on a speed-time graph shows how the speed of an object changes as it moves.
• A description of an object’s motion includes a reference point, a direction from the reference point, and a distance.
• Speed is the distance traveled by an object in a unit of time. Velocity includes both speed and direction of motion.
• Acceleration is a change in velocity. Velocity changes when either the speed, the direction, or both the speed and the direction change.
Which term refers to the distance between an initial position and a final position?
A. displacement
B. distance
C. motion
D. speed
A. acceleration
B. distance
C. motion
D. speed
Which is the measure of how quickly the velocity of an object changes?
A. average speed
B. displacement
C. distance
D. time
On a speed-time graph, what does the x-axis show?
1. You must use a reference point to describe an object’s motion.
2. An object that is accelerating must be speeding up.
Do you agree or disagree?