Motion Vocabulary

Position Location of an object with respect to its reference point. (distance and direction)

Reference Point A point to which other points and locations are referred to. Usually known as the initial position and equal to 0. Example: John is 20 meters away from his home. (the reference point in this example is John’s home)

Scalar Quantity specified by only magnitude (a #) Ex: mass, time, speed, distance

Vector Quantity specified by magnitude (a #) and direction. Direction can include: north/south/east/west, + or - , up or down, right or left, etc. Ex: displacement, velocity, acceleration

Distance Scalar Quantity (mag only) Unit: meter (m) The total amount of length traveled by an object. Ex: John runs 20 meters east then 10 meters west. John’s distance that he ran was 30 meters

Displacement Vector quantity (mag & dir) Unit: meter (m) Straight line distance from the final position to the initial position. Ex: John runs 20 meters east then 10 meters west. John’s displacement is 10 meters east from where he initially began. Δ x = final x – initial x

Speed Scalar quantity (mag only) Unit: meter/second (m/s) Distance covered divided by the amount of time taken to cover that distance: Ex: John runs 20 meters east in 10 s. John’s speed is: s = d/t = 20 m/10 s = 2 m/s.

Velocity Vector quantity (mag & dir) Unit: meter/second (m/s) Displacement of object divided by the amount of time. Ex: John runs 20 m east then 20 m west in 10 seconds. John’s velocity is: v = Δx/t = 0 m/10 s = 0 m/s

Acceleration Vector quantity (mag & dir) Unit: [meter/second]/second (m/s2) Change in velocity divided by the amount of time. Ex: John changes his speed from +20 m/s to +15 m/s in 10 seconds. John’s velocity is: a = Δv/t = (15-20)/10 = -5 m/s (the negative indicates slowing down in this instance)

Motion Equations Xf - Xi