unit 12: force and motion / lesson 1: speed, velocity, and ... · msf8.2c distinguish the motion of...

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