MSF8.2c Distinguish the motion of an object by its position, direction of motion, speed, and acceleration and represent resulting data in graphic form in order to make a prediction. (DOK 2)
Unit 12: Force and Motion / Lesson 1: Speed, Velocity, and Acceleration
Motion: when an object’s position changes from one place to another
Reference point: place or object used to determine if something is in motion.
• BEST type of reference point is an immovable object
Formula to find speed:
*miles/1 hour (mph)*meters/1 second (m/s)*steps/1 minute
Speed: the distance an object travels in one unit of time•This is an example of a UNIT RATE
Constant speed: speed is the same at all times during the motion or movement
Because objects do not usually travel a constant speed over long distances, we find:
Average speed: total distance divided by total time
Bethany walked 3 miles in 3 hours on Monday. She then walked 6 miles in 5 hours on Tuesday. On Wednesday, Bethany completed her journey back home which consisted of 9 miles in 8 hours. What was her average speed?
Total distance = 3 + 6 + 9 = 18 milesTotal time = 3 + 5 + 8 = 16 hoursAverage speed = 18 miles = 1.1 mph 16 hours
PRACTICE PROBLEM #1
Mr. Hannigan types very quickly. For a presentation, he typed 120 words in 2 minutes. He went on to type 70 words in 1 minute. Before finishing, he typed another 230 words in 3 minutes. How many words per minute did Mr. Hannigan type?
PRACTICE PROBLEM #2
Average speed = 420 words = 70 words per minute 6 minutes
Distance –Time GraphsX-axis = time Y-axis = distanceSlope: slant of line on graph = SpeedIf it’s a: Straight line on the graph, then it =
constant speed
•When comparing 2 lines on this type graph, the steeper line = faster speed.
Comparing Speeds on a Distance Time Graph
Which line would mean
faster? distance
time
Distance Time Graph and Changing Speed.
Slope is decreasing = slowing down.Horizontal line = no motion.Slope is increasing = speeding up.
Velocity: speed in a given direction (north, south, east, west, etc.)
*Hurricane Omar is moving at 25 kph in an easterly direction toward the Cayman Islands.
*Maranda was driving at a speed of 65 mph west on Highway 98 towards Columbia.
Basic unit of length in SI is meter.
Smallest to largest mm, cm, m, km
Graphing motionScale: tells us how much or how many•INTERVALS MUST BE EQUALLY SPACED!
Points: show us the data that has been collected
A line graph is useful for displaying data that changes over time.
Which line would mean faster?
distance
time
Distance-Time Graph Practice Problem #1
Which of the graphs show that one of the runners started 10 yards further ahead of the other?
Graph A
Distance-Time Graph Practice Problem #2
In Graph D, which of the runners is fastest?
Runner #1
Distance-Time Graph Practice Problem #3
Calculate the speed of Runner #1 for Graph D.
S = d t
S = 20 yd 4 s
S = 5 yd/s
Distance-Time Graph Practice Problem #4
Calculate the speed of Runner #2 for Graph D.
S = d t
S = 10 yd 4 s
S = 2.5 yd/s
Acceleration.• Acceleration is a measure of the change in
velocity during a period of time.• An object’s velocity changes when it
speeds up, decreases speed, or changes direction.
• Like velocity, acceleration has a direction and can be represented with an arrow.
Average Acceleration
• Average acceleration is a change in velocity during a time interval divided by the time interval which the velocity changed.
• Formula : a = Final speed – Initial speed total timeUnit = m/s2
Velocity-Time Graph Practice Problem #1
What is the average acceleration from 1.0-4.0 seconds?At 1.0 seconds the initial velocity (or speed) is 40 m/s. At 4.0 seconds the final velocity (or speed) is 100 m/s.
Average acceleration =
Final speed - initial speedtotal time
Average acceleration = 100 m/s - 40 m/s = 60 m/s = 20 m/s2
3 s 3 s
Velocity-Time Graph Practice Problem #2
What is the average acceleration from 4.0-6.0 seconds?At 4.0 seconds the initial velocity (or speed) is 100 m/s. At 6.0 seconds the final velocity (or speed) is 60 m/s.
Average acceleration =
Final speed - initial speedtotal time
Average acceleration = 60 m/s - 100 m/s = - 40 m/s = - 20 m/s2
2 s 2 s