Vector Or Scalar ?

In an exam remember what must be the simplest mnemonic ever : V=V, S=S you`ll see why here.

What is the difference between a Scalar and a Vector ?

Here`s the simple answer and what you need to repeat every time you are asked

"Scalars have magnitude i.e. size , Vectors have magnitude and direction'


Any time a unit is just `how much` - it is a scalar. examples -
So mass is measured in kg, - how much mass do you have ? so scalar (e.g. 25kg)
Speed is measured in m/s - how fast is the car going ? so scalar (e.g. 5m/s)

When you need `how much and what direction` - it`s a vector examples - So Velocity - how fast is the car going forwards ? Vector (i.e. +10m/s) Velocity - How fast is the car going backwards ? Vector (e.g. -5m/s)
Your go :
Weight - it`s a force pulling you down, it has a direction so what is it Scalar or Vector ?
Light Intensity - it`s a measure of how much light, it doesn`t have a direction so what is it Scalar or Vector ?
Answers at the bottom so you don`t see them until you`ve shown yourself you have had a chance to answer.


The two things to compare is speed and velocity - Does Speed have a direction ? No - so Scalar Does Velocity have a direction ? Yes - so Vector
One reason to concentrate on the Speed and Velocity is the mnemonic. They each have the appropriate initial so use them as checks in your head V=V, S=S.
And look back at Speed above, no sign, Velocity examples above have signs to tell you the direction.
Now - Explain it to someone to get it into your head.


More advanced - only if you are very comfortable with all the above, otherwise it might confuse you.
So velocity is a vector because it has a direction, acceleration also has a direction (positive means Velocity is increasing, Negative means Velocity is decreasing)
A car is going forward with an initial velocity (V_I) of +10m/s.We accelerate and the velocity increases to a final velocity (V_F) of +15m/sSo V_I and V_F were both positive..... so was the acceleration because change in the Velocity was positive (+5m/s)
A car is going forward with an initial velocity (V_I) of +10m/s.We decelerate and the velocity decreases to a final velocity (V_F) +1m/sSo V_I and V_F are still both positive (+10m/s. +1m/s).... but the acceleration was negative because the velocity decreased (-9m/s)

Tips :
When you come to look at Newton`s Laws always think in terms of velocity (vectors) - and that means no movement is just a velocity of 0m/s.


Answers :
Weight is a Vector, any force is a vector because forces act in a direction.
Light Intensity is just `How much light` so no direction, just an amount and therefore it`s a Scalar.