Determining Position

“Hey, Is This Thing Moving?”

Position Position is defined relative to a

reference point and reference directions.

Reference Points and Reference Directions Three things must be included:1.) A reference point – a starting point

used to describe the position of an object.

2.) A reference direction that describes which way to move in relation to the reference object.

3.) A distance from the reference point.

Reference Points and Reference Directions The flagpole can be used as a reference point for finding the bicycle. (Can you give directions to locate the bike?)

Reference Points and Reference Directions A plus sign (+) indicates movement in

the direction of the reference point. A minus sign (–) indicates movement

in the direction opposite of the reference point.

The description of an object’s motion also depends on the reference point chosen.

Position as a Vector A vector is a quantity in which two things

must be specified: Distance from the reference point

(represented by the length of the arrow)

Direction from the reference point (represented by the direction the arrow is pointing)

Positions in Two Dimensions Objects that do not

move in straight lines require two reference directions.

A car traveling from San Diego to Sacramento doesn’t move in a straight line. (What direction would we say it is traveling?)

Positions in Two Dimensions In this map of a city, the art museum is located ___________m west and ___________m south of the bus station.

1,000

250

Changing Position The change in an object’s position is

called its displacement.

Changing Position Displacement is the difference

between the initial position and the final position of an object.

Changing Position Displacement includes a size and a

direction. Displacement is a vector.

Changing Position Direction of displacement is the

direction from starting point to end point.

Size of displacement is the distance from the starting point to the ending point.

Distance and Displacement

Distance __________Displacement __________

40 m40 m East

Distance and Displacement

Distance __________Displacement ________________

70 m50 m Northeast

Distance and Displacement

Distance __________Displacement _________

140 m0 m

Displacement is a(n) ____ because it has both size and direction.

A speed

B velocity

C vector

D acceleration

1.1 Determining Position

Position is defined relative to ____.

A a reference point and a vector

B displacement and reference directions

C a vector and reference directions

D a reference point and reference directions

1.1 Determining Position

Which of the following statements is true?

A Displacement and distance traveled are always the same.

B Displacement and distance traveled are never the same.

C Distance traveled is the direction of the displacement vector.

D Displacement and distance traveled are the same if the direction does not change.

1.1 Determining Position

What must you have to determine a position?

A acceleration

B velocity and speed

C reference point and origin

D reference point and reference direction

SCI 1.a