# Explaining equations easy way

Hi,
today I want to talk about simple physical equations and how you can check if they are right or not.

Lets start with the equation of distance in the most simple way.  How do you find this formula anyway? Well we want to know how distance traveled is calculated.

s=…

Now on the right side there should be something that corresponds to distance. There has to be time because we are talking about traveling in some time.

s=t…

Distance also depends on how fast you are traveling, which means velocity has to be there. Now if both time and velocity are bigger you will get also bigger distance so there will be multiplication between them.

s=v*t

From this we can conclude that:

v=s/t     this makes sense because velocity will be big when you travel for short time great distance.

t=s/v     this too makes sense because time will be great when you will go slowly great distance.

This is all intuitive, you do not remember any equations because those you can always get just from pure logic.

I can follow with the equation of inertia:

p=…

Inertia describes basicly how hard it is to stop something. Just from personal experience, when is it hard to stop something? When it is heavy and when it is fast.

p=m*v

What units will inertia have? Well you can always compare only same units so the units that come up from “m*v” must be the units of inertia.

p=m*s/t (now here we have the basic units)

p=kilograms*meters/seconds

The unit of inertia is kilogram on meter per second!

Those equations that have only two parts can be made really fast this way if you do not remember it exactly.

There is this important part with the same units. When you do some problem in physics you usually first just take all the letters and try to combine them until you get the final “sentence” and then you enter all your values. This is very effective and it is good to check you final equation, look at this for example:

P=m*g*s/t

Here it would be hard to imagine if it makes sense like we did with the formula for distance but we can get insert all the units and check if the right side is the unit for P – performance. (here m is mass, g is gravitational acceleration, s is distance, t is time). We know that the unit of performance is watt and watt is: kg*meter^2/second^3

So now for the equation we insert the values:

P=(mass*(meter/second^2)*meter)/second

P=kg*meter^2/second^3

Now we know that we are right even though we maybe started with P=W/t (W is work) and we were not sure if the conversion was right. The units correspond to what we know about performance.

Dragallur