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Mechanics help with direction of forces watch

1. When there is a question on an inclined plane, when do you draw the force parallel to the plane and horizontal to the plane? Because the particle is going up the plane so why do you sometimes draw the force horizontally to the plane? Thanks
2. (Original post by coconut64)
When there is a question on an inclined plane, when do you draw the force parallel to the plane and horizontal to the plane? Because the particle is going up the plane so why do you sometimes draw the force horizontally to the plane? Thanks
This depends on the question. In general the only force that will act parallel to the plane is friction, or maybe some given force which is specifically said to act up or down the plane. Components of other forces (well usually just weight) will act parallel to the plane though, but in general you will draw the force in the direction it acts and then use trig to calculate components (but you can always use dotted lines to show components or something if it helps to visualise).
Sometimes you get a force which is specifically said to act horizontally, so you draw it horizontally, that's basically all there is to it.
3. (Original post by 13 1 20 8 42)
This depends on the question. In general the only force that will act parallel to the plane is friction, or maybe some given force which is specifically said to act up or down the plane. Components of other forces (well usually just weight) will act parallel to the plane though, but in general you will draw the force in the direction it acts and then use trig to calculate components (but you can always use dotted lines to show components or something if it helps to visualise).
Sometimes you get a force which is specifically said to act horizontally, so you draw it horizontally, that's basically all there is to it.
Okay, thanks for the reply but I just don't understand why it will go towards the plane though as the object is going up. But I guess that's just mechanics..
4. (Original post by coconut64)
Okay, thanks for the reply but I just don't understand why it will go towards the plane though as the object is going up. But I guess that's just mechanics..
If you mean a force pushing horizontally into the object and the object moving up, consider the force as the hypotenuse of a right angled vector triangle; the other two sides are parallel and perpendicular to the plane. You should see that the component of the force parallel to the plane is pointing up the plane; hence the force pushes the object up the plane.
5. (Original post by 13 1 20 8 42)
If you mean a force pushing horizontally into the object and the object moving up, consider the force as the hypotenuse of a right angled vector triangle; the other two sides are parallel and perpendicular to the plane. You should see that the component of the force parallel to the plane is pointing up the plane; hence the force pushes the object up the plane.
Oh okay, I think that's what I had to do in one of the questions. So I just need to read the question properly then. Thanks. Could u help me with question 1f by any chance?

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