# Question on force

batballbat
if two forces act simulataneously on a body how can we show than one force does not effect the action of the other force? (provided they are acting obliquely)
Specifically, how can we show that the acceleration of one force remains the same in that direction?

## Answers and Replies

Staff Emeritus
Gold Member
if two forces act simulataneously on a body how can we show than one force does not effect the action of the other force? (provided they are acting obliquely)
Specifically, how can we show that the acceleration of one force remains the same in that direction?

I'm not sure what you're asking. Forces obey the superposition principle. The basic idea is that the total force acting on a body is the vector sum of all the individual forces acting on that body.

batballbat
sorry u didnt understand my question. i ask it again: how is the parallelogram addition proved?

Gold Member
You posit that forces are vectors. Vectors obey the parallelogram law.

This is true by definition. What's the prove?

batballbat
did i?
somebody help me with this

batballbat
actually the first question is what i want. parallelogram follows from it.
if two forces act simulataneously on a body how can we show than one force does not effect the action of the other force? (provided they are acting obliquely)

Gold Member
You essentially want a proof of a definition. This was what I was trying to get at. Force is defined to be a vector quantity, therefore forces add by vector addition.

batballbat
why is force a vector? why not electrical current?

Gold Member
It's a definition. What much else can I say? You make models of how the universe works. In those models you need to make some clear definitions. If your model describes the universe correctly then you keep it, if not, you get a new model.

I don't get what you are looking for.

batballbat
my question arised when the vector addition of acceleration was not clear in my mind

Langston
Newton described the concept that forces act independently and add as a parallelogram as:

“A body, acted on by two forces simultaneously, will describe the diagonal of a parallelogram in the same time as it would describe the sides by those forces separately.”

This was done before the concept of vectors and is one of the reasons that vectors are defined the way that they are. Presumably Newton and others got the notion from observation and experiment. I don't know what setup they used to prove it but if you want to show that two forces acting simultaneously on a body don't affect each other you'll have to go to the lab measure the affect of one force then the other applied individually and then measure them applied simultaneously.

I feel like there should be a standard classroom experiment to show this but I can't think of one off hand.

VICKZZA
I have a question too
what should be the value of the work,if vertical component is 2/3 time to the hoizontal component of the applied force,while the displacement in the direction of applied force is x metres?
plz give me a complete solution.....

Staff Emeritus