Unit 02Linear Motion

Introduction to Motion ~Notes~

Linear Motion --- Key Words

• Displacement– The straight line distance drawn from the object’s

initial position to the object’s final position• ΔX= Xf-Xi

• Velocity – The displacement divided by the time interval during

which the displacement occurred.• V = ΔX/Δt

• Acceleration– The rate of an object’s change in velocity.

• a = ΔV/Δt

Scalars vs. Vectors• A Scalar is …

–Magnitude (amount)

• A Vector is …–Magnitude and direction

Physics vs. Everyday VocabularyScalar Vector

Distance(just “how far”)

Speed (just “how fast”)

Speed up, slow down

Displacement(“how far” and which direction)

Velocity (“how fast” and which direction)

Acceleration (direction of change in

velocity, including change in direction)

Identify if the following quantities are vectors or scalars

• 5 meters West• 78m/s • 94m/s2 Up• -40m• 10 meters• +15m/s

Vector

Vector

Scalar

ScalarVector

Vector

Which way is the object moving?

(right or left)• A boy drives his car with a velocity of -6m/s.RIGHT! (negative direction)

• A cat walks and has a displacement of +8m.LEFT (positive direction)

• A car drives with a velocity of 4m/s and an acceleration of -2m/s2.RIGHT (positive velocity = positive direction)

Does the object Speed Up or Slow Down?

• A car drives east with a velocity of 6m/s and has an acceleration of +3m/s2.

(Velocity(+) and acceleration(+) are in the SAME direction)–Speeds Up

• A boy runs west as the wind pushes and accelerates him east.

(Velocity(-) and acceleration(+) are in the OPPOSITE direction)–Slows Down

• A boy on a skateboard moves with a velocity of +5m/s and accelerates himself at a rate of -2m/s2.

(Velocity(+) and acceleration(-) are in the OPPOSITE direction)–Slows Down

If an object moves with a constant

velocity, what is it’s acceleration?

ZERO!!!!It does not speed up or slow down!

Activity• 6 students will run and walk a

variety and distances and speeds while the other students record the data of time and position.

• These data will be analyzed as a class

Velocity5 meters 10 meters 15 meters 20 meters 25 meters

Runner #1Time (s)

Runner #2Time (s)

Runner #3Time (s)

Runner #4Time (s)

Runner #5Time (s)

Runner #6Time (s)

Runner #1 & Runner #2

Runner #3 & Runner #4

Runner #5 & Runner #6

Displacementa) What is the total distance covered by runner #1?

b) What was the total displacement of runner #1?

c) What is the total distance covered by runner #6?

d) What was the total displacement of runner #6?

Displacementa) What is the total distance covered by runner #1?

b) What was the total displacement of runner #1?

c) What is the total distance covered by runner #6?

d) What was the total displacement of runner #6?

ΔX = Xf – Xi

ΔX = 25m – 0mΔX = 25m

ΔX = Xf – Xi

ΔX = 15m – 0mΔX = 15m

25m

35m

Velocitya) Compare runner #1 and #2, how do the slopes of the graphs show you who

is faster?

b) Using the graph, how can you tell runner #3 slowed down?

c) Using the graph, how can you tell runner #4 sped up?

d) Using the graph, what did runner #5 do when they reached the 15m point? How can you tell?

e) Using the graph, at what point did runner #6 turn around? How do you know from the graph?

Velocitya) Compare runner #1 and #2, how do the slopes of the graphs show

you who is faster?

b) Using the graph, how can you tell runner #3 slowed down?

c) Using the graph, how can you tell runner #4 sped up?

d) Using the graph, what did runner #5 do when they reached the 15m point? How can you tell?

e) Using the graph, at what point did runner #6 turn around? How do you know from the graph?

Runner #1 is faster – because they have the steeper slope! Steeper slope means faster velocity on a position vs. time graph.

Because the slope changed from a small slope to a steeper slope. This shows a change in velocity, acceleration, he went faster.

Because the slope changed from a steep slope to a less steep slope. This shows a change in velocity, acceleration, she went slower.

Runner #6 turned around when the slope changed from + to – at 7 seconds. + slope means he was runner to the right, but the – slope means he turned around and ran to the left!

The runner stopped. The slope was zero at that point.

Accelerationa) Using the graphs, which runners accelerated?

How do you know?

Accelerationa) Using the graphs, which runners accelerated?Runners #3, 4, 5 and 6 all accelerated.

I know because the slope of the graph changed for each of those runners.

A change in slope shows a change in velocity (speed).Runner #3 sped up Runner #4 slowed downRunner #5 stoppedRunner #6 changed direction!