http://www.ck12.org Chapter 2. One-Dimensional Motion
2.2 Speed and Velocity in One Dimension
Objectives
- Define constant speed and velocity.
- Distinguish between speed and velocity.
- Determine velocity from position-time graphs.
Vocabulary
- average speed:Total distance traveled divided by total travel time.
- average velocity:Change in position divided by change in time.
- uniform speed
- uniform velocity
Equations
Average speed equation and uniform speed equation:
v=xt, wherexis the total distance traveled andtis time.
This equation is equivalent tor=dt ord=rt, wheredis distance andris rate.
Average velocity equation and uniform velocity equation:
∆v=(tf∆−xti), where∆x= (Pf−Pi)
Average Speed and Instantaneous Speed
Suppose you are travelling along a long straight highway. You start driving, and an hour later, you are 100 km
away. Youraverage speedis the 100 km/hr. The information you have is time and distance. You can calculate
your speed by dividing the distance you’ve traveled by the time of travel.
Speed=
distance
time=
∆x
∆t=
100 km
1 hour=100 km/hrDuring the hour that this trip took, your speedometer may have many different readings. You might have been
traveling faster during the first part of the hour, and then slower in the second half. The reading on the speedometer
is your instantaneous speed.
If you go back on a return trip, the calculation of the speed is the same. The result is still 100 km/hr (also
abbreviated "kph" for "kilometers per hour"). Like distance, speed is a scalar quantity and thus always positive. The
speedometer reading is the same no matter what direction you are driving in. Speed cannot provide information
about direction.