Why does a 400 cos 45° force produce clockwise rotation?

[goldfish9776]

Homework Statement

for the 400cos45 force , i think it should rotate anticlockwise, am i right? but the book gave it is rotated counterclockwise...

Homework Equations

The Attempt at a Solution

 

[SteamKing]

Homework Statement

for the 400cos45 force , i think it should rotate anticlockwise, am i right? but the book gave it is rotated counterclockwise...

Homework Equations

The Attempt at a Solution

Uhh... "anticlockwise" and "counterclockwise" both mean the same thing, you know, "not clockwise".

RIP, Yogi Berra

 

[goldfish9776]

Uhh... "anticlockwise" and "counterclockwise" both mean the same thing, you know, "not clockwise".

RIP, Yogi Berra

Typo, imo it should be in counterclockwise, right? The book gave it in clockwise direction..

 

[SteamKing]

Typo, imo it should be in counterclockwise, right? The book gave it in clockwise direction..

Nope, guess again.

The moment sign convention adopted by the book is a little unconventional. I prefer the right hand rule, which would make CCW moments positive.
The actual convention chosen doesn't matter, as long as you remain consistent throughout your calculations.

 

[goldfish9776]

Nope, guess again.

The moment sign convention adopted by the book is a little unconventional. I prefer the right hand rule, which would make CCW moments positive.
The actual convention chosen doesn't matter, as long as you remain consistent throughout your calculations.

I'm wondering is my direction of 400cos 45 force correct ? Should it point to the left ?

 

[goldfish9776]

Nope, guess again.

The moment sign convention adopted by the book is a little unconventional. I prefer the right hand rule, which would make CCW moments positive.
The actual convention chosen doesn't matter, as long as you remain consistent throughout your calculations.

 

[SteamKing]

I'm wondering is my direction of 400cos 45 force correct ? Should it point to the left ?

Yes, it is correct.

 

[goldfish9776]

Yes, it is correct.

then the moment should be anticlockwise , right ? by using right hand rule . I bent my finger from f to F , since it's r cross F

 

[SteamKing]

then the moment should be anticlockwise , right ? by using right hand rule . I bent my finger from f to F , since it's r cross F

The moment you showed in Post #6 is indeed CCW.

 

[goldfish9776]

The moment you showed in Post #6 is indeed CCW.

Ok, then the book is wrong...

 

[SteamKing]

Ok, then the book is wrong...

No, the moment shown in the book is properly CW.

The figure you drew in Post #6 does not match the layout of forces shown in the book, and the direction of that moment is CCW.

You can't change the position of the force relative to the axis of rotation without changing the direction of the moment which is produced.

 

[goldfish9776]

No, the moment shown in the book is properly CW.

The figure you drew in Post #6 does not match the layout of forces shown in the book, and the direction of that moment is CCW.

You can't change the position of the force relative to the axis of rotation without changing the direction of the moment which is produced.

I m confused now. Then can you show mew the r x f diagram in the book? I have no idea at all.

 

[SteamKing]

I m confused now. Then can you show mew the r x f diagram in the book? I have no idea at all.

It's Fig. 3-27(a). Point A is located about half way up the y-axis, while the 400 N force is located about 0.8m from the origin.

You don't need a lot of diagrams and whatnot to figure this out. If point A is the point about which a force causes rotation, you should be able to visualize this from a picture if you can see where the force is applied relative to point A.

 

[goldfish9776]

It's Fig. 3-27(a). Point A is located about half way up the y-axis, while the 400 N force is located about 0.8m from the origin.

You don't need a lot of diagrams and whatnot to figure this out. If point A is the point about which a force causes rotation, you should be able to visualize this from a picture if you can see where the force is applied relative to point A.

since the author assume clockwise as positive here , so shouldn't the positive 400cos45 (0.3) rotate anticlockwise? i have drawn a diagram for the moment in the previous post , showing it is rotated in anticlockwise direction... i can't understand why the moment is in clockwise direction for the author...