# Is there a difference between negative acceleration and retardation

1. Jun 22, 2014

### PhysicsStudnt

Kindly elaborate on the difference between negative acceleration and retardation...if they are different

2. Jun 22, 2014

### PhysicsStudnt

Say if body is moving backwards / in negative direction and with a decreasing velocity, do we consider it as negative(negative (acceleration)) = positive acceleration.......?

3. Jun 23, 2014

### ehild

Acceleration is a vector quantity and its sign is given with respect to the chosen positive direction. Retardation or deceleration is connected to speed. A body decelerates if it slows down, that is, its speed is decreasing.
The acceleration is positive when a body travels to the negative direction with decreasing speed. Remember that acceleration is defined as (change of velocity) over (time taken): a= (v(t+Δt)-v(t))/Δt at the limit Δt→0. Both v and a are vectors.
If the body travels along the negative x axis, v(t)<0. If it decelerates, |v(t+Δt)|<|v(t)|, so v(t+Δt)>v(t). (v(t+Δt)-v(t))/Δt >0

ehild

4. Jun 26, 2014

### PhysicsStudnt

Thank you Ehild for helping me out with my doubt....i also reffered some youtube videos...what i infered was that, if acceleration occurs in the same direction of velocity, and displacement, the particle will speed up....and if its moving in negative direction, all 3 quantities are bound to be negative....but when acceleration is in the direction opposite to the motion, or velocity, the particle will slow down...that is when we call it retardation....
And i believe it is connected with net unbalanced force...when net unbalanced force is in opposite direction of motion, the particle is eventually bound to slow down and stop...and if net unbalanced force is in the same direction as that of motion, the particle will gain more speed...and that could be in the negative direction too....
This is what i infer.....
once again thank you soo much for the timeyou spent in answering my question....god bless you...

Last edited by a moderator: Jul 3, 2014