# Fluids - Pascal's Principle / Negative vs Positive

• crono_
In summary, the problem involves calculating the weight that can be lifted by a hydraulic jack with specific dimensions and a maximum force of 110 N. A question is raised about the textbook's notation of forces as positive and negative, and a potential explanation is given.
crono_

## Homework Statement

The handle of a hydraulic jack is 15 cm long and is pivoted 2.5 cm from the input piston which has a radius of 0.60 cm. The output piston has a radius of 1.2 cm. What weight could be lifted by the jack if the person pushing on the handle is to exert no more than 110 N of force?

http://edugen.wiley.com/edugen/courses/crs2216/cutnell3550/ssg/cutnell3255c11/image_n/nw0002-y.jpg

## The Attempt at a Solution

Silly question...I doubt I'm right, as I'm hardly an authority to go up against a textbook. But that being said...

I'm confused as to why the textbook (Cutnell & Johnson Physics Study Guide 7th ed.) says that F is positive when F1 is negative? They're both pointing down...so...aren't they both negative? F2 is positive and pointing upwards, that makes sense. But why F is also positive completely eludes me...

Am I missing something completely obvious?

On a side note - I hope I'm not violating any copyright laws by posting that diagram. I just want the answer, not a prison term!

Any thoughts?

crono_ said:

## Homework Statement

The handle of a hydraulic jack is 15 cm long and is pivoted 2.5 cm from the input piston which has a radius of 0.60 cm. The output piston has a radius of 1.2 cm. What weight could be lifted by the jack if the person pushing on the handle is to exert no more than 110 N of force?

http://edugen.wiley.com/edugen/courses/crs2216/cutnell3550/ssg/cutnell3255c11/image_n/nw0002-y.jpg

## The Attempt at a Solution

Silly question...I doubt I'm right, as I'm hardly an authority to go up against a textbook. But that being said...

I'm confused as to why the textbook (Cutnell & Johnson Physics Study Guide 7th ed.) says that F is positive when F1 is negative? They're both pointing down...so...aren't they both negative? F2 is positive and pointing upwards, that makes sense. But why F is also positive completely eludes me...

Am I missing something completely obvious?

On a side note - I hope I'm not violating any copyright laws by posting that diagram. I just want the answer, not a prison term!

Perhaps they are summing the moments about the hinge in order to determine the force F1. So maybe they chose the + moment in the CCW direction (making F x d positive). Then the reaction at F1 (F1 x (d-2.5)) would be negative since it would cause a CW rotation.

Just a thought.

CS

## 1. What is Pascal's Principle?

Pascal's Principle, also known as the principle of transmission of fluid-pressure, states that a change in pressure at any point in an enclosed fluid will be transmitted equally to all points in the fluid.

## 2. How does Pascal's Principle apply to fluids?

Pascal's Principle applies to all fluids, including liquids and gases. It states that a change in pressure at one point in an enclosed fluid will be transmitted equally to all other points in the fluid, regardless of the shape or volume of the container.

## 3. What is the difference between negative and positive pressure?

Negative pressure, also known as vacuum or suction, refers to a pressure that is lower than the surrounding atmospheric pressure. Positive pressure, on the other hand, refers to a pressure that is higher than atmospheric pressure.

## 4. How does negative pressure affect fluids?

Negative pressure can cause fluids to be drawn into a container or a vacuum. In other words, the fluid will move from an area of higher pressure to an area of lower pressure.

## 5. How does positive pressure affect fluids?

Positive pressure can cause fluids to be pushed or squeezed out of a container. In other words, the fluid will move from an area of higher pressure to an area of lower pressure.

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