Check your Understanding Ch 4 ("Conceptual Physics" Hewitt)

speed =

• $\frac{ending\ \ time\ -\ starting\ \ time}{2}$

• $\frac{dis\tan ce}{time}$

• $\Delta t$

• distance x time

Which of the following are legitimate for describing speed?

• miles/hour

• light-years per century

• centimeters per day

• kilometers per minute

• all of these

Instantaneous speed is

• the first speed measured

• speed measured with a stopwatch

• the speed of an object at any instant

• the most recent speed measured

Average speed is

• not the fastest, but not the slowest either

• the average of two or more instantaneous speeds

• the total distance covered divided by time interval

• what shows on a car's speedometer

Speed is a description of how fast an object moves; velocity is

• the same as speed

• something faster than speed

• how fast AND in what direction

• something that is always changing

Acceleration

• applies to increases as well as decreases in speed

• is related to how fast something is moving

• is the rate at which velocity is changing

Acceleration =

• going really fast

• not a vector quantity

• the amount speed changes

• $\frac{change\ in\ velocity}{time\ interval}$

Free fall

• is falling without accelerating

• is an object moving under the influence of gravity only

• involves air resistance

• is falling at a constant speed

During each second of free fall

• acceleration depends on an object's mass

• an object falls about ten meters

• the instantaneous speed on an object changes by about 10 m/s

When acceleration is expressed as m/s² ("meters per second squared" or "meters per second each second") the unit of time, the second, occurs twice -

• once as part of speed, again for time interval during which speed changes

• once in initial speed, again in final speed

• and I've always wondered about that

• we need to take speed twice to measure acceleration