3.1 Position, distance & displacement Pg. 5 in NB.

3.1 Position, distance &displacementPg. 5 in NB

Objectives

• Describe motion in 1D using position, distance, and displacement.

• Analyze motion in 1D using position, distance, and displacement.

• Correctly use and interpret positive and negative values of position and displacement.

Physics terms

• origin

• position

• distance

• displacement

Equation & Variables

– In words the final position equals the initial position plus any displacements

• final position• initial position

(might see as • displacement

Rearranging the Equation•  

Describing motion

Before you can predict an object’s motion, you need to be able to describe it.

How do we describe an object’s position?

Engaging with the concept• Based on the interactive…

– What is the difference between distance & position?

– What’s the difference between distance & displacement?

Origin

• Your origin is just your starting point (i.e. where you came from)

• If a problem does NOT tell you where you start from you can assume it’s origin (i.e. initial position) is at 0.

Position Key Points• Tells you where you are relative to an origin

(i.e. specific spot)• Positive and negative position tells you if

you’re in front or behind OR to the left or right of the origin

• TOTAL amount of ground you covered/traveled

• ALWAYS POSITIVE• Does NOT tell you your exact location• NO direction included

Distance Key Points

Displacement Key Points

• CHANGE in position• Tells you how far you are from the origin (i.e.

starting point)• Can be positive OR negative

– Positives & negatives tell you direction

Displacement & Direction• Positive displacement

implies object moved: up/North or right/East

• Negative displacement implies object moved: down/South or left/West

+-Left - Right

West - East

-

+Up

Down

North

South

Vector vs Scalar

Vectors have both magnitude (#) and direction (+ or -)!

Scalar values have only magnitude (just a #; always positive).

clip

Displacement is a vector

Displacement is a vector because it contains direction information.

Distance is a scalar

Distance is a scalar quantity.

It does NOT include direction information.

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Adding displacements

An ant starts at 2 m, and crawls forward 7.1 m. Then it turns around and crawls back 5.5 m. What is the ant’s final position?

Answer: 3.6 m

Problem SolvingEx: A boat sails 50 km north then 800 km south. What is the boat’s final position?

What do you choose as the boat’s initial position?• xi = 0 km

What are the displacements?»

What is the final position?• xf = -750 km OR 750 km south

What is the car’s initial position?• 0 m

What is the car’s displacement(s)?• 200m east (or +200m) & 600m west (or -600m)

What is the car’s final position?• 400m west of the origin (or -400m)

What is the car’s distance traveled?• 800m

1. A robot car moves 200 m east, turns around and moves 600 m west.

Assessment

2. A woman starts at x = -10 m and has three successive displacements of -5 m. What is her final position?

Answer: xf = -25m

Assessment

3. What displacement moves an object from a position of 25 meters to a position of -15 meters?

Answer: d = -40m

4. If a bird ends at a position of 270m west of the origin & has a total displacement of 173m before it stops, what was the bird’s initial position?

Assessment

5. A ball rolls from an initial position of 9.6m to a final position of 2.1m.

a. What is the displacement of the ball?

b. What’s the distance traveled by the ball?

c. Why are they different?

Homework