Lesson 1 - Describing Motion: Reference Frames and Acceleration

Vocabulary flashcards covering reference frames and acceleration concepts from Lesson 1, Section 4 (p. 16-17).

Reference frame

A point of view for describing motion, specifying the speed and direction of motion relative to a chosen point; frames are arbitrary and must be stated.

Car reference frame

A reference frame in which the car is at rest (velocity 0) and objects outside move relative to the car.

Road reference frame

A reference frame in which the road is at rest (velocity 0) and objects inside the car appear to move.

Arbitrary reference frame

A reference frame that can be chosen freely; motion descriptions depend on which frame is used and must be specified.

Velocity

The speed and direction of an object's motion; velocity changes when either speed or direction changes.

Speed

How fast an object moves, regardless of direction.

Acceleration

The rate of change of an object's velocity; occurs when speed changes, direction changes, or both, and is measured in m/s².

Positive acceleration

Acceleration when velocity increases over time; the object's speed or forward velocity increases per unit time.

Negative acceleration

Acceleration when velocity decreases over time (slowing down); velocity becomes smaller with time, often called deceleration.

Deceleration

Slowing down; a form of negative acceleration where speed decreases over time.

Changing direction as acceleration

An object can accelerate by changing direction, even if its speed remains constant, such as turning a corner.

Average acceleration

The overall rate of velocity change over a time interval; a_avg = (ending velocity − starting velocity) / time.

Acceleration units

Units of acceleration are meters per second squared (m/s²); velocity is in m/s and time in s.