To move an object, I have to apply a force.

[/quote]

actually, if object is already in uniform motion, no external force is require. or simply Newton 1st Law

to change the motion of an object, yes a force is needed or simply Newton 2nd Law, F[sub]net[/sub] = m*a

[quote author=leeyiren link=topic=1960.msg7234#msg7234 date=1285386022]

But F=ma

Hence every time I apply a force there will be acceleration.

So how do you move an object at constant velocity?

[/quote]

if we look at F[sub]net[/sub] = m*a

let P be the push force

f be the friction force opposes motion v

then F[sub]net[/sub] = m*a

imply P - f = m*a

constant v imply a = 0,

therefore, it is possible if P - f = 0

how can we relate this to real life situation?

when a ball falls under gravity from a tall building for a long time, terminal velocity is reached

let mg is weight of mass, m under gravity g

let D be drag force on mass m

using F[sub]net[/sub] = m*a

mg - D = m*a

at terminal velocity, a = 0

mg - D = 0

[quote author=leeyiren link=topic=1960.msg7234#msg7234 date=1285386022]

PS: Why are there so few ppl are posting questions in this section?

[/quote]

no everyone leaves a question,but there many views. ;D