# Why does $d$ mean?

I am told that force can be given as a rate of change of momentum:

$$F = \frac{p}{t} = \frac{dp}{dt}$$

What do the $d$'s mean? I've seen them in other formulas as well.

• Reading your equation literally they just mean that numerator and denominator have been multiplied by $d$, where it has been tacitly assumed that $d\ne0$. Apr 9, 2014 at 9:38

In the equation you have given $F = \frac{p}{t}$
But in general, the change in p with respect to t might not be constant, and thus the fraction must be represented by a derivative, which represents the rate of change of some quantity with respect to another one, in this case $\frac{dp}{dt}$ represents the rate of change of p with respect to a small change in t.