- #1

heroslayer99

- 33

- 6

- Homework Statement
- This isn't really a set homework so I don't have anything to write here sorry.

- Relevant Equations
- Suvat formulae

Hi

I was just wondering about the suvat formulae and a question popped into my head, which I'd like someone to try and explain the reason as to why please.

So I know that when we have a formula such as F=ma or v = u + at, you can evaluate the magnitude of both sides and arrive at a scalar form of said equation, which is what I think that we use most of the time. However say if we had the scalar form of the first suvat equation, namely mod(v) = mod(u) + mod(a)t, I know that this is a correct mathamatical statement however we usually like to know the direction of our vector in physical situations, so we put a - sign Infront of each quantity which is going in our deemed negative direction.

However we also know that a scalar quantity (watch how I said quantity and not just a scalar) cannot be negative, so when we use a suvat formula and accompany a quantity with a negative sign, we must be using the vector form right? However it makes no sense to say that because we usually use the magnitude of each vector (which is a scalar) and not the vector in it's i/j or column form. So I'd just like to ask, why can we use negative signs in suvat formula if we aren't using the vector form, as a scalar quantity cannot be negative.

I was just wondering about the suvat formulae and a question popped into my head, which I'd like someone to try and explain the reason as to why please.

So I know that when we have a formula such as F=ma or v = u + at, you can evaluate the magnitude of both sides and arrive at a scalar form of said equation, which is what I think that we use most of the time. However say if we had the scalar form of the first suvat equation, namely mod(v) = mod(u) + mod(a)t, I know that this is a correct mathamatical statement however we usually like to know the direction of our vector in physical situations, so we put a - sign Infront of each quantity which is going in our deemed negative direction.

However we also know that a scalar quantity (watch how I said quantity and not just a scalar) cannot be negative, so when we use a suvat formula and accompany a quantity with a negative sign, we must be using the vector form right? However it makes no sense to say that because we usually use the magnitude of each vector (which is a scalar) and not the vector in it's i/j or column form. So I'd just like to ask, why can we use negative signs in suvat formula if we aren't using the vector form, as a scalar quantity cannot be negative.

Last edited by a moderator: