THE BIG MOVERS – HYDRAULICS

Most machines that move very large objects use a hydraulic system.

Recall that a HYDRAULIC SYSTEM is a system that uses a liquid under pressure to move loads via pistons and tubing.

A PNEUMATIC SYSTEM is a system that uses gas under pressure to move loads.

Before hydraulic systems were invented most construction projects were accomplished using manual labour and animals.

            Ex) Pyramids, castles, great wall of china

PRESSURE IN FLUIDS

Recall that in unit A we discovered the following:

PRESSURE is the Measure of the amount of force applied to a given area.

Pressure  (Pa) = Force (N)/Area (m²)

Pressure is measured in Pascals (Pa)

PASCAL’S LAW:

Pressure applied to an enclosed fluid is transmitted equally in all directions through out the fluid.

• fluids do not become compressed, unlike gases.

• pushing force (pressure) is transmitted equally in all directions within the fluid (I wrote it twice, because it’s super important)

HOW TO CREATE PRESSURE

A PISTON CREATES PRESSURE

Hydraulic systems work because of pistons.

PISTON:

A disk that fits tightly inside a cylinder.

• As the disk moves it either draws fluid/gas in or pushes fluid/gas out

• Commonly used in engines and hydraulic systems

• Size can vary widely

A hydraulic system uses a liquid under pressure to move loads. It combines a smaller piston in a pipe, attached by a flexible tube to a larger piston in a larger pipe.

• Pushing the smaller piston requires small amounts of force but the piston must move a greater distance

• As a result the larger piston pushes with a large amount of force but it moves a smaller distance

INPUT PISTON:

Used to apply force to the fluid (smaller piston)

OUTPUT PISTON:

Transfers the force to the load (larger piston)

CALCULATING MECHANICAL ADVANTAGE USING PRESSURE

From Pascal’s law, we know that the pressure the small piston creates is the same everywhere in the fluid. So the large piston has a larger area and is able to multiply the pressure because of its larger area. The force and area at each piston act as ratios that have to be equal.

Small Piston Pressure = Large Piston Pressure

So... We can say that:

Force of the Small Piston / Area of the small piston = Force of the Large Piston / Area of the large piston

Re-written we express it as such: 

F (small)/A (small) = F (large)/A (large) 

PRESSURE EXERTED EQUALLY IN THE FLUID PROVIDES THE MECHANICAL ADVANTAGE.

Mechanical Advantage (MA) =  Output Force/Input Force

HYDRAULICS QUESTIONS

CHECKPOINT 1

EVALUATING & improving Machines

Machine:

A combination of mechanical devices which together apply forces and control movement to perform an intended action.

Function:

The purpose of a machine/mechanical device. (Machines can have more than one purpose)

Design:

How a device appears (aka its ‘form’). The design should suit the function.

Machines and mechanical devices have evolved over time because of science and the development of new technologies. The design and function of a machine is related to its efficiency and effectiveness.

Look at the wheels above, has their design evolved? How is their design better? How do we evaluate a better design?

Q: So how do people (engineers/designers) know which mechanical device is the best?

A: They use a set of criteria to evaluate and analyze the mechanical device. (AKA we need a system to keep score!)

Criteria need to be specific to properly evaluate a machine/mechanical device:

1. Design

   • Is there a better design to complete it’s function?

2. Effectiveness

   • Does it fulfill it’s function well without breaking for prolonged periods? (ex. gas powered mower vs. push mower)

3. Efficiency

   • Is it performing work efficiently? (ex. using a push mower takes longer to mow the lawn)

4. Price

   • Is it expensive to build?

   • Is it easy to manufacture, can it be manufactured quickly?

5. Unwanted costs

   • Does it create wastes? (ex. Gas powered lawnmower has more parts than a push mower)

   • Can we make it less harmful for the living environment ? (ex. Gas powered lawnmower releases greenhouse gases)

6. Aesthetics

   • Does it look pleasing to the eye, does it need to look pleasing?

7. Environment

   • Perhaps the device works great only in certain environments? (ex. BMX bike for Tour de France)

   • Is it being used safely? (ex. single speed bike in a BMX course)

8. Ergonomics

   • How well do humans interact with the device?

evaluate the following mechanical device:

Evaluate different versions of a mechanical device using the criteria given. (ex, vehicle from 1900, 1950, 2000)

CSA :

A non-government association that tests and approves a wide range of products to ensure they are safe for use by the consumer. CSA stands for Canadian Standards Association. 

CHECKPOINT 2

Technological advances and mechanical devices

Technology and devices have come a long way since the invention of simple machines. Advances in technology can have broad implications on human society:

• Changes in society

• Changes in the environment

• Changes in production capacity

• Changes in human behaviour

Watch the following video and write down all the different changes in society, human behaviour, environment, and production capacity. 

CHECKPOINT 3

Evaluation of Mechanical Devices Assignment

Evaluating Mechanical Devices

Visual Presentation Rubric