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