- #1
clarkie_49
- 6
- 0
Hi all,
While reading through physics history book, i en counted an attempt to show the very basics of Leibniz notation; the following is shown:
If
s = (1/2)gt^2, then
s + ds = (1/2)g(t + dt)^2
s + ds = (1/2)gt^2 + gtdt + (1/2)gdt^2, then because of the first line
ds = gtdt + (1/2)gdt^2
It then goes on to say (1/2)gdt^2 "can be ignored because it is so small". Obviously this is not really correct, and i was looking for a way to explain using limits. I came up with something, but it seems incorrect in some way?
If
ds = gtdt + (1/2)gdt^2, then
(ds/dt) = gt + (1/2)gdt . Let (ds/dt) = f, then
lim f {dt -> 0} = gt
However, the confusion is that this does not seem to imply
(ds/dt) = gt as is normally written; it seems to imply
lim f_{dt -> 0} = lim (ds/dt)_{dt -> 0} = gt
Can somebody please explain how Leibniz would have came to (ds/dt) = gt without "ignoring (1/2)gdt^2" ? Was the notion of a limit used back then?
Thanks in advance,
Brendan
While reading through physics history book, i en counted an attempt to show the very basics of Leibniz notation; the following is shown:
If
s = (1/2)gt^2, then
s + ds = (1/2)g(t + dt)^2
s + ds = (1/2)gt^2 + gtdt + (1/2)gdt^2, then because of the first line
ds = gtdt + (1/2)gdt^2
It then goes on to say (1/2)gdt^2 "can be ignored because it is so small". Obviously this is not really correct, and i was looking for a way to explain using limits. I came up with something, but it seems incorrect in some way?
If
ds = gtdt + (1/2)gdt^2, then
(ds/dt) = gt + (1/2)gdt . Let (ds/dt) = f, then
lim f {dt -> 0} = gt
However, the confusion is that this does not seem to imply
(ds/dt) = gt as is normally written; it seems to imply
lim f_{dt -> 0} = lim (ds/dt)_{dt -> 0} = gt
Can somebody please explain how Leibniz would have came to (ds/dt) = gt without "ignoring (1/2)gdt^2" ? Was the notion of a limit used back then?
Thanks in advance,
Brendan