## Pulse

A forum set up for physics questions from students in the courses PHYS1121, 1131, 1221 and 1331 at the University of New South Wales. It is intended for questions that cannot readily be answered in class,
either because they fall outside the main syllabus and therefore would be distraction (however interesting) or for other reasons.

Moderator: msmod

Suvekchhya
Posts: 10
Joined: Sat Jun 07, 2014 7:13 pm

### Pulse

When a pulse travels towards the right of a string, why is the f(x0) = f(x' - vt) ? why is it negative?
with x0 being position at t = 0 and x' being position at t = t
Thankyou
a.s.h.
Posts: 110
Joined: Tue Jan 28, 2014 3:50 pm

### Re: Pulse

Is it because x' = x0 + vt, so x0 = x' - vt?
joe
Posts: 755
Joined: Fri Aug 29, 2003 11:57 am
Location: Sydney

### Re: Pulse

Consider a point in the wave pattern, e.g. the crest of the wave. Let's put the crest at x=0 when t=0. If that crest moves to the right at v, then the x value of the crest and t increase together. f(x-vt) allows the argument to remain zero as t increases.

See the animations at
http://www.animations.physics.unsw.edu. ... ing-waves/

Joe