# Re: interference fit

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> All OK too. Just to make terms easier, acceleration, in either direction
> is still acceleration, or increasing velocity over time. Deceleration is
> slowing down, reducing velocity over time, direction of motion up or
> down is irrelevant.

Unfortunately, in this case, we have to take direction into consideration.

If you ask a physicist, you will get definitions like:

speed = distance / time, direction irrelevant
velocity = distance / time, along with the direction of travel
acceleration = change in _velocity_ / time

At this point, it is best if we drop the term 'deceleration'.

The simplest equation to look at is that for velocity:

v = u + at

v is velocity, u is initial velocity, a is acceleration and t is time.

>From this, you can see if acceleration is positive, velocity will
increase and if acceleration is negative (what you might call deceleration),
velocity will decrease.

For example, if you are going forwards (slowly, don't do this) and throw
a slushbox into reverse, this will create a negative acceleration
and after a while you start going backwards, a negative velocity.
Throw it into drive again, positive acceleration, eventually
that 'at' term in the equation cancels out the negative velocity
and you start moving forwards.

I'll scan the relevant picture either tomorrow or Monday...

Orin.

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