When you want to pull downward to lift something the main advantage of passing a rope upward and through a single pulley rather than just up over the branch of a tree is that the pulley that?

Answer 1

reduces friction

reduces friction

There is less friction in the pulley than around the branch of a tree so it is easier to lift the object - and easier to drop it too- be careful!

A fixed pulley has only one function, to redirect your applied force, Fe.

"Changes the pulling direction" - (Nothing gained but we do get to pull down instead of lifting upward. This is an advantage and could save your back.)

Reduces friction - when using the pulley. - but not what the question is asking.

The main advantage is that fricton if reduced, lessening the force required to lift the something. Other "advantages," if any, are secondary.

changing the pulling direction...both branch and pulley change the direction of force. What the pulley does is remove the friction of the rope sliding over the branch. Imagine a rope wrapped around the rim of a wheel, and as you pull one end of the rope, the wheel spins. This is the same principle, in that a pulley is made up of grooved wheel and axle, and the rope fits inside of the groove along the rim of the wheel. The wheel rolls freely, removing the friction of the rope moving thru it.

Answer 2

In that situation, the main advantages of the pulley are: 1). The pulley changes the direction of your force with much less friction than the tree branch does so that more of your work goes toward lifting the load, and less of it toward cutting bark. 2). You're free to place the pulley where it's needed ... exactly above the load ... thus minimizing the force required to lift it even though the pulley has no mechanical advantage. The tree branch doesn't offer this flexibility.

Answer 3

A single pulley can change the direction of the force.

Answer 4

Reduces friction