Motion: Why we need acceleration?

1. Jul 25, 2012

koolraj09

Motion: Why we need acceleration??

Hi guys!!
While studying motion of any object we need displacement (say, x) of the object(to locate the object from some reference)to describe it's motion at any time instant.
Next to compare the motion (like how fast the object moves)we need to determine velocity/speed of the object.
But why do we need acceleration to describe the motion? Aren't displacement & velocity enough? Is it necessary that we need to know the acceleration of the object to describe the complete motion?

Now if at all we need acceleration(dv/dt) then why don't we consider jerk,snap etc.(the subsequent derivatives of displacement) to describe an object's motion?
Note: I am talking about any general motion and not necessarily rectilinear translation.
Thanks.

2. Jul 25, 2012

jbriggs444

Re: Motion: Why we need acceleration??

Because we can usually predict the various forces that a body might be undergoing based on its position and its velocity.

By Newton's second law, acceleration is proportional to force.

That means that we can write down an equation of motion in terms of position, velocity and acceleration.

By contrast, there is not usually a way to predict jerk, snap, crackle or pop other than by taking the first, second, third and fourth derivitives of acceleration. So there are no useful equations that we can write down.