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9.1 Describing and Measuring Motion, 9.2 Speed and Velocity, and 9.3 Acceleration
Transcript of 9.1 Describing and Measuring Motion, 9.2 Speed and Velocity, and 9.3 Acceleration
9.1, 9.2 and 9.3
START HERE (1/13)
9.2 Speed and Velocity
9.1 Describing and Measuring Motion
Chapter 9: Motion
Describing and Measuring Motion
Speed and Velocity
Motion and R.P.
MOTION: an object is in motion if its distance from another object is changing.
To determine if you are moving, you use a Reference Point (RP): A place or object used to determine motion.
You and a friend decide to go skydiving. Describe all of the reference points you might use while in the air to tell that you are in motion.
Relative Motion -The actual motion of an object relative to another object. May be more than one motions.
International System of Units
ISU: scientists use common measurements so that they can communicate easily.
The SI unit of lenth is the meter (m)
SPEED: The distance an object travels per unit time.
Can be any unit of distance over a unit of time (m/s or km/h or cm/s or mi/h)
AVERAGE SPEED: total distance/total time
INSTANTANEOUS SPEED: Rate at which an object moves at a given time.
(W) When you know both the speed and direction of an object's motion, you know the velocity of the object.
VELOCITY: speed in a given direction!
X-Axis = time
Y-Axis = distance
Slope= the steepness of a line (rise/run)
Lets pretend ACP Oakland is planning an Olympic Style competition. Mrs. Lundberg wants suggestions for possible events.
You have 5 minutes to design an activity, game, or contest (feel free to be creative!) where the winner is determined by SPEED. Your idea needs to have a name and an illustration depicting the basic concept of what each participant/player will do.
Write your idea on a white board, each one will be displayed after 5 mins!
ACCELERATION: The rate at which velocity changes.
Is acceleration only increasing?
(W) Acceleration is increasing, decreasing, or changing direction
I started at a red light (0 m/s), and was clocked after 10 seconds going 30 m/s.
What is my acceleration?
(W) Acceleration is measured in meters per second squared (m/s )
Speed vs time graph
Distance vs Time
What are some examples of Acceleration?
Here is a little story: Shannon is peacefully driving home after school, and notices the red traffic light ahead. She begins to slow down. She hears music as she approaches and wonders where it's coming from. That's about the time she sees the shaking Ferrari in the lane next to her. Nice car, she thinks. Nice sound system. Shannon turns green with jealousy. But just as she starts to pull up next to him, the light turns green. She instantly stops decelerating and puts the pedal to the metal. I'll show him who's boss, she thinks. But her beat-up '88 Honda Civic just doesn't cut it. In about a quarter mile he's already passing her; in a mile she can't even see him anymore.
How did he do that? Shannon was way past him before he even started moving! Acceleration. The rate at which speed is increased. (Also one of the more interesting things to graph!) We have to assume values for several variables from this scenario, like Shannon's speed as she neared the stop line, the reaction times of both drivers, the traction of their tires, wind speed, wetness of the road, etc. You get the picture - this isn't exact. But the following graph shows just how powerful acceleration can be.
Now, come up with your own story and graph to model acceleration....
(W) You can use both a speed-versus-time graph and a distance versus-time graph to analyze the motion of an accelerating object.
(W) A slanted, straight line on a speed-versus-time graph means that the object is accelerating at a constant rate. You can find your acceleration by calculating the slope of the line.
slope = the change in the y axis over the change in the x axis.
Write a summary at the end of your notes.
Do section 1 questions 1 and 2 on page 311
In a group of 1-3, draw an example of motion on a white board. Label and describe at least two reference points and the relative motion for each.
*Remember to convert between different metric lengths, simply move the decimal according to the prefixes.
speed: 10 m/s
velocity: 10 m/s North
Most objects do not move at a constant speed, graphs can represent multiple speeds for one motion.
On the plate, draw a line towards the top of the plate for a starting line, and a line towards the middle of the plate for a finish line.
Measure and record the distance between the two lines on the plate.
Stack two textbooks to use as a lift for the plate.
Ms. Schmidt will come around and give you a "squeeze" of honey on the starting line.
Lift the plate and lean it against the books on around the spot of the starting line.
Use the timer to measure how long it takes the honey to reach the finish line. Record.
On a scrap piece of paper, calculate and write your speed, write your names, and hand it to Ms. Schmidt.
I will pair you up, both partners will have whiteboards.
Partner one will write a "motion story" and read it out loud to partner 2.
Partner two will draw a distance-time graph that describes the motion described in Partner's story.
Both partners will check to see if the story and the graph make sense.
Goal: To understand how speed is calculated
1. Time yourself and your partner for at least 2 distances. One must be 15m.
o Distance #1: 15m Time#1:
o Distance #2: 10m Time#2:
o Speed #1
Q: How could a car be accelerating if it is going a constant 65 mph?
A: The car could be turning.
Watch this video on distance vs time graphs:
Create your own distance vs time graph:
With a partner, discuss the three examples of acceleration in the following picture:
How does the distance change each second for the plane above?
The slanted, straight line on this speed vs time graph tells you the cyclist is accelerating at a constant rate.
You can represent the motion of an accelerating object with a distance-versus-time graph. Figure 9 shows a distance-versus-time graph for your bike ride. On this type of graph, a curved line means that the object is accelerating. The curved line in Figure 9 tells you that during each second, you traveled a greater distance than the second before.
Do a section summary and all sections of Chapter 9.3 Assessment Questions 1-5.