http://www.ck12.org Chapter 2. One-Dimensional Motion
FIGURE 2.2
The odometer (300,000 miles) shows the
distance the car has traveled and the
speedometer shows the instantaneous
speed of the car (61 mph).- Displacement (ex. 30 miles due west) and
- Velocity (ex. 30 mph due west)
Check Your Understanding
- Which statement best describes a vector quantity?
a. A race car moving at 110 mph
b. A turtle strolling at 200 cm/min
c. An SUV moving at 40 km/h eastAnswer: C, since both speed and direction are given. Speed is considered the scalar component of velocity.
- Is time a scalar or a vector quantity?
Answer:We do not associate any direction with time, since we cannot choose to move in whatever direction we
wish through time. This is not to say that t = -3.0 s has no meaning. It simply refers to a situation that occurred three
seconds before our observation began. It does not imply that we can move backward in time.
Position
We need to know where things are, both in the context of daily life and in the complexities of modern science.
Physics defines the location of an object by assigning a position to it. Just as with mathematics, physics typically
uses a coordinate system. The coordinate system must have a zero point or origin in order to properly reference
position. Since we are discussing one-dimensional motion we will use the simplest coordinate system- a number
line with a marked zero, negative values to the left of zero, and positive values to the right of zero.
Distanceis a scalar quantity giving the positive length between two points. The total length for a series of distances
can be computed by adding the absolute values of each length segment.X=|P 1 −P 2 |+|P 2 −P 3 |+...