When to use sine vs cosine in pressure force formulas?

[AmirWG]

What's the difference between
P = FSin Angle / A
P = FCos Angle / A
Why cannot we use F / A only in both forumlas? I am really confused
When I should use each one of these forumlas ? I just need someone to explain each one of them ... Here's a pic to what I am referring to

, why cannot we always use the big F in the middle
Thanks In advance .

 

[phinds]

What's the difference between
P = FSin Angle / A
P = FCos Angle / A
Why cannot we use F / A only in both forumlas? I am really confused
Thanks In advance .

You need to add parentheses to show what it is that your statements are supposed to mean

 

[scottdave]

What's the difference between
P = FSin Angle / A
P = FCos Angle / A
Why cannot we use F / A only in both forumlas? I am really confused
Thanks In advance .

Please give some context as to how these angles are presented in the situation.

 

[AmirWG]

When I should use each one of these forumlas ? I just need someone to explain each one of them ... Here's a pic to what I am referring to https://ibb.co/M1GJRPF , why cannot we always use the big F in the middle , the question might be lame but I just suck when it comes to dealing with forces, I am sorry for not being specific .

 

[davenn]

Here's a pic to what I am referring to https://ibb.co/M1GJRPF ,

posting your image on that site with the correct orientation would stop everyone turning on their side to read it

 

[AmirWG]

posting your image on that site with the correct orientation would stop everyone turning on their side to read it

 

[osilmag]

Because F is not perpendicular to the surface you have to multiply by the cos or sin of theta.

 

[ZapperZ]

When I should use each one of these forumlas ? I just need someone to explain each one of them ... Here's a pic to what I am referring to https://ibb.co/M1GJRPF , why cannot we always use the big F in the middle , the question might be lame but I just suck when it comes to dealing with forces, I am sorry for not being specific .

You need the component of F that is perpendicular to the surface. Think about it. If F is close to being parallel to the surface, is there a lot of force being applied to that surface?

You should never simply apply a formula blindly. You need to understand what the physics is, and what physical issues are involved. Do not simply use a formula without understanding what it is saying.

Zz.

 

[scottdave]

Like @ZapperZ said, you want to consider the component which is perpendicular to the surface. Notice where the Θ is positioned in each of the pictures. You could just say "I'm only going to measure the angle from the surface", like the picture on the left. Then you use Sine. But if they give you a different angle, you may need to calculate the proper angle to take the sine of.

 

[sophiecentaur]

@AmirWG The following applies throughout Science (and life)

Do not simply use a formula without understanding what it is saying.

You be fair to the OP, I would take issue with the two quoted diagrams because they are using the same symbol for different angles. If they had used, say θ and φ then you would possibly have noticed that θ + φ = 90°. The rest is trigonometry.
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