In this lesson you will learn about acceleration. In basic physics terms,
acceleratin is the change in velocity over a period of time. Generally acceleration is
interpreted as speeding up, but in physics it can mean either speeding up or slowing
down. The formula for acceleration is a = (vf - vo)/t, where a is the
acceleration, and the rest of the stuff you saw in a previous lesson.
Let's do a problem together. A falling skydiver slows from a speed of 52m/s to
8m/s in 0.8s as the parachute opens. What is the diver's acceleration?
What do we know?
aNo, that's what we're looking for.
voYes, its -52m/s
vfYes, its -8m/s
tYes, its 0.8s
You may be asking why the velocities are negative. The diver is going down, so the
value becomes negative. Be careful and keep track of your signs while doing these
problems.
Now plug in the values and work the problem.
a = (-8m/s - (-52m/s))/0.8s
a = 55 m/s
Wait!! Why did the answer come out positive? I thought if an object went down it
was negative.
Good point, but there's one thing you forgot. Granted the diver is going down, but
he is also slowing down. Two negatives make a positive. For problems such as this just
follow this simple chart:
| Speeding Up | Slowing Down | |
|---|---|---|
| East, North, or Up | (+) | (-) |
| West, South, or Down | (-) | (+) |
The next lesson will combine the two previous, and
introduce some new substitution equations.
