Re: [Phys-l] Deltas in equations

[Herbert Schulz <herbs@wideopenwest.com>]

On Apr 27, 2006, at 5:28 PM, Larry Smith wrote:

> Knight's PSE is also usually very good about the Delta's.  For  
> example, his
> kinematic equation for uniform acceleration is
> s_f = s_i + v_is Delta-t + (1/2) a_s (Delta-t)^2;

Howdy,

This, of course, is WRONG! If you do the integration you get

x_f = x_i + v_i*(t_f - t_i) + (1/2)*a_x*(t_f^2 - t_i^2)

so the last term does NOT have a (t_f-t_i)^2 = (Delta t)^2.

Good Luck,

Herb Schulz
(herbs@wideopenwest.com)