# 5 Kinematic Equations?

by harujina
Tags: equations, kinematic
 P: 75 I know that there's 5 key equations for motion which is: d = (vf+vi/2)t vf = vi + at d = vit + 1/2at^2 vf^2 = vi^2 + 2ad d = vft - 1/2at^2 Correct? But my teacher was confusing me today and he taught us these two other equations: d = 1/2(vi+vf)t d = 1/2at^2 What are these? Are they just other "rules of motion" like everything else?
 P: 59 The second equation 'D=1/2at^2' is one of the kinematic equations 'D=Vi+1/2at^2' where the initial velocity 'Vi' is considered to be zero.
P: 75
 Quote by quawa99 The second equation 'D=1/2at^2' is one of the kinematic equations 'D=Vi+1/2at^2' where the initial velocity 'Vi' is considered to be zero.
oh right, i can't believe i didn't notice that! ok thank you!

Mentor
P: 11,255

## 5 Kinematic Equations?

 Quote by harujina d = (vf+vi/2)t
This one is incorrect. Either your teacher or you copied it wrong.

 d = 1/2(vi+vf)t
This is the correct version, assuming you meant (1/2)(vi+vf)t.

Actually, only two equations are essential:

vf = vi + at
d = vit + (1/2)at2

The others can be derived from these two.
 P: 49 5 eq v final velocity u initial vel. t time s displacement a constant accn v= u +at s= ut + .5at2 v2= u2 +2as s= vt - .5at2 s= .5(v+u)t
P: 49
 Quote by jtbell This one is incorrect. Either your teacher or you copied it wrong. This is the correct version, assuming you meant (1/2)(vi+vf)t. Actually, only two equations are essential: vf = vi + at d = vit + (1/2)at2 The others can be derived from these two.
but while doing numerical it is irritating to first get acceleration, so actually 5 eqn
are good adding to it this gives feel to a child what he's doing
also kinematics it a beginning so one can learn these quickly as afterward formula formula formula!!!
P: 1,282
 Quote by jtbell Actually, only two equations are essential: vf = vi + at d = vit + (1/2)at2 The others can be derived from these two.
You can chose any two out of the five to take as essential and derive the other three from them
 Mentor P: 11,255 True, but I like those two because if you know calculus you can get them by integrating d2x/dt2 = a twice. Of course, that means you really need to remember only one equation which basically just says "acceleration is constant."

 Related Discussions Introductory Physics Homework 8 Introductory Physics Homework 6 Introductory Physics Homework 2 Introductory Physics Homework 2 Introductory Physics Homework 29