here more detailed…
you start from nothing…is it ok when I say our speed is 0 ( s = d/t, do not move d = 0, so s = 0)…any objection?
You stay still mean S = 0
now your are moving faster and faster …the speed is changing
acceleration is a changing of speeds…within certain time periods…is it clear? the sign would be a positive…remember getting faster is always positive….
if you start from nothing to 8 m/s in 4 second
how much is the acceleration?
acceleration is (8 m/s – 0)/4 = 2m/s2 (meter per second square)
How about biking? do you like it?
initial speed is 25m/s to 50 m/s in 10 second, how much is the acceleration?
need any help?
How about this….you are getting slower…you are exhausted
initial speed or velocity is 10 m/s to 5 m /s in 5 second, how much is the acceleration?
(5m/s – 10m/s)/ 5 s = -1 m/s2 see the negative sign for acceleration
you can call it deceleration…..
make sense now?