We have an expression . If this expression is multiplied by 1, we get a result same as the given expression i.e. .
It means that the number 1 multiplied with the expression had no effect on it as we got the same expression.
This is called the multiplicative identity of 1 according to which any time you multiply a number by 1, the result or the product is that original number.
For anything to do with force you have to assume an even amount of force is spread out evenly. But for things like growing rate you have all those variables so you can't assume a constant growing rate like acceleration.
