# Understanding What A Normal Force Is

#### jot_dain

Hello all

I know this may sound like a simple question but i am struggling to get my head around the concept of a Normal Force.

I know that the definition of a Normal Force is the force that is perpendicular to the surface the object in question makes, but i am trying to visualize this.

I have an object of some mass that is stationary on a sloped surface at angle theta (no friction forces exist).

As this object is stationary the ground exerts an equal and opposite reaction force.

I have tried to show this in my diagram below:- This is where i get a confused.

Am i correct in thinking that the reaction force can be split into two component forces.

I have tried to show how i have split the reaction force into two below:- As you can see that i have split the Reaction Force into two Forces F2 which is my Normal force because it is perpendicular to the ground.

And a secondary force which i have called F3 - but what would F3 be called?

Also would the angle Theta be the same at the corners i have shown?

I hope this makes sense?

Thank you.

#### Woody

There are a number of mistakes.
You have your right angle triangle round the wrong way,

I would have broken down the F1 force into components. Note that the F1 force should be the hypotenuse (longest side) of the triangle.
You would then get the Normal Force perpendicular to the slope and the XXXX force (or F3) is parallel to the slope.
Note that the Reaction Force is now Balancing the Normal Force.
F3 is now the portion of the F1 force that is not balanced by the Reaction Force
i.e. F3 is the portion of the F1 force that will cause the block to slide down the slope.
Note that $$\displaystyle F1=\sqrt(F2^2+F3^2)$$ (not just F2+F3).

• donglebox and topsquark