you're in for it now, i have a degree in physics and plan on continuing school in the future as i would love to teach it.
the seconds per second can be a bit confusing to visualize.
lets start with some basics
velocity is the speed at which an object is moving in relation to some inertial frame of reference (the earth in most cases). when you are travelling at 60 miles per hour, which happens to be 88 feet per second, that means that every second that passes - you travel 88 feet. simple.
the next stage is acceleration, this is the rate of change of velocity. when you drive around, you dont instantly travel 60 mph, you must accelerate to it. some cars have much more acceleration than others, they are able to get to 60 much faster. we all know this is how fast the car accelerates. this acceleration is really defiined as the rate of change of velocity (how fast your velocity increases in a given time)
so to answer your question, when you see something like ft/sec^2, that means ((feet per second) per second). i used the parenthesis to illustrate the meaning. your velocity is feet per second. it helps if you say it to yourself slowly. velocity is how many feet per second i am moving (ft/sec). acceleration is how fast my velocity is changing per second, like saying change in velocity per second. substitute in ft/sec for velocity and say ft/sec.........per sec
lets say your acceleration is 22 ft/sec^2. that means that for every second that passes, your velocity increases by another 22 ft/sec. after 1 second you would be going another 22 ft/sec, so take the initial velocity of 0 ft/sec, then add 22 ft/sec and end up with 22 ft/sec. after 2 seconds you have an additional 22 ft/sec, so now you add the 22 ft/sec + another 22 ft/sec to get 44 ft/sec. then 66, then 88. so an acceleration of 22 ft/sec is 0-60 in 4 seconds. thats fast!
when you get deep into it, there are endless amounts of rates of change that could be factored in. for example take personal experience. lets say you got 0-90. we all know that the car is fastest 0-30, then a bit slower 30-60, then even slower from 60-90. so would could find the average acceleration, but its just the average. the rate of acceleration itself is changing too (now thats ft/sec/sec/sec) even thats changing and so on and so forth.
if you want to play around and have some fun take some basic equations and data. i am ignoring air resistance for these
gravitational acceleration at earth's surface:
32 ft/sec^2
9.82 m/sec^2
formulas:
x=Vot+1/2at^2
Vf=Vo+at
Vf^2+Vo^2=2ax
where x is distance, Vf is velocity final, Vo is velocity original, a is acceleration, and t is time
you can do some fun stuff with these.
a car goes from 0mph to 100mph in 10 seconds, what is its average rate of acceleration?
use Vf=Vo+at and convert 100mph to ft/sec so units match
100 mph = 146.7 ft/sec
146.7=0+(a)(10) 146.7=a10, divide each side by 10 to find a
a=14.7 ft/sec^2
a car is travelling at 30 mph and accelerates at 10 ft/sec^2 for 5 seconds, how far did it travel in those 5 seconds?
use x=Vot+1/2at^2 and convert the mph to ft/sec so units match
30 mph=44 ft/sec
x=(44)(5)+(1/2)(10)(5^2)
x=220+125
x=345 feet
you throw a ball directly upward into that air, it goes to a peak height of 20 feet. what was the ball's initial velocity when it left your hand?
use Vf^2+Vo^2=2ax
we know that the ball, when it reaches it peak height, will stop for an instant, then begin falling back down. so at its peak height, where it stops for an instant, we know its final velocity is 0.
0+Vo^2=(2)(32)(20)
Vo^2=1280
Vo=35.8 ft/sec
some people will choose to use -32 ft/s, since its fighting agaisnt gravity and its actually DECELERATION. if you do that you end up with trying to find the square root of a negative number, which will end with an imaginary number, velocity cannot be an imaginary number. this technique will work if you remember that the 20 feet that the ball travelled upward should be a negative distance too, which will again result in the square root of a positive number.
now for a cool question, let say:
you fire a rifle directly upward, its muzzle velocity is 1000 ft/sec. ignoring air resistance, how high with the bullet go? how long will it take for the bullet to reach its peak height? how long will it take the bullet to hit the ground after you fire it? what will its speed be when it hit the ground? you fire it from a height of 6 feet, right by your head!!!!
yeah i'm a total nerd, now hand in your assignment on time!!!
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