Question

What does Δx stand for? What SI units are used to measure it?

Answer 1

Answer:

Speed is the rate at which distance is covered. Speed can be measured using a number of units (mph, km/h, cm/yr, ft/s)...all with a unit for distance on top and a unit for distance on the bottom, but the SI units are m/s. It is a scalar quantity because it looks at distance, and distance does NOT take into account direction. Speed can NEVER be negative; it is always going to be positive. Your speedometer on a car reads distance; even if you are traveling in reverse, the speed is still positive. Speed is the distance covered per unit of time.

Velocity is the rate that position changes (or displacement). Velocity can also be measured in a variety of units (mph, km/h, cm/yr, ft/s), ...all with a unit for distance on top and a unit for distance on the bottom, but the SI units are m/s. It is a vector quantity because it looks at displacement, which means that direction is taken into consideration as well as magnitude. Velocity can be positive OR negative. The sign implies the direction of the displacement. Negative means that is is moving to the left (sometimes called West) or down (sometimes called South); positive means that is moving to the right (sometimes called East) or up (sometimes called North). If no direction is given, then "to the right" is the default. Velocity is the displacement per unit of time.

The following equations are for constant and/or average speed & velocity. If the motion changes, then a constant acceleration equation is required.

Constant/Average Speed & Velocity Equations

S = D/t

vavg = Δx/t

vavg = (x - x0)/t

Each equation contains 3-4 variables. Listed below are many of the possible pertinent variables you will encounter.

Variable Symbol

Variable Name

SI Unit

Other Possible Units

Specifics

S

speed

meters per second (m/s)

mph, km/h, ft/s Speed is the rate at which distance is covered. Because it is a scalar quantity, it can never be negative. The change in speed can be negative, but not speed itself.

vavg velocity (average, constant, uniform) meters per second (m/s)

mph, km/h, ft/s

Velocity is the rate at which an object's position changes. Because it is a vector, direction is taken into account. Be careful with your negatives and positives. A positive velocity means the object is moving up, forward, or to the right. A negative velocity means the object is moving down, backward, or to the left.

t or Δt time; change in time

second (s)

min, hr, dy, wk

Time can be the total time or the time for that portion of the problem. Because it is a scalar quantity, it can never be negative.

Δx displacement; change in position

meter (m)

mi, km, cm, in, ft, yd

Displacement is the change in position of an object. It is the length and direction of the straight line from the origin to the finish. Because it is a vector, direction is taken into account. Be careful with your negatives and positives. A positive displacement would mean moving up, forward, or to the right. A negative displacement would mean moving down, backward, or to the left.

x

final position

meter (m) mi, km, cm, in, ft, yd The final position is where the object ends. Because it is a vector, direction is taken into account. Be careful with your negatives and positives.

x0

initial position

meter (m) mi, km, cm, in, ft, yd

The initial position is the origin, where the object starts. Because it is a vector, direction is taken into account. Be careful with your negatives and positives.

D

distance

meter (m) mi, km, cm, in, ft, yd Distance is the total length traveled by an object. Because it is a scalar quantity, it can never be negative.