Pneumatic systems are often used to move objects. This activity is your opportunity to build a simple pneumatic device.
PR O B L E M SO L V E R
• Move the plunger of one syringe up and the plunger of a second identical syringe down. Connect them with plastic tubing.
• Place your hand on the plunger that is up. Investigate what happens when you depress the plunger.
1 What do you notice about the plunger on the other syringe?
2 Compare what you observed in this activity to your observations of a simple hydraulic lift. Create a Venn diagram of the similarities and differences in the systems.
3 Summarize what you discover. Use the vocabulary you have learned in this unit.
A pneumatic system is filled with gas.
bronchiole
left lung lung
tissue
bronchus windpipe
smaller branch of bronchus alveoli right
lung
The human lungs are a natural pneumatic system.
In the next activity, you have a chance to apply your understanding of the compressibility of gaseous fluids to a pneumatic device.
Air-Bag Systems as Protection
Because gases exert a force when they expand, they are often used to protect people and objects from injury. Since the 1980s, airbags have been installed in vehicles to help save lives.
Vehicle air-bag systems are pneumatic systems that include a crash sensor, ignitor, gas generator, and inflatable bag. The sensor is able to detect a collision equal to running into a wall at 16–24 km/h. From there, chemicals mix to form a reaction similar to a rocket booster, which creates a large volume of nitrogen gas. This pressurized gas inflates a nylon bag in less than a tenth of a second, causing it to burst out of the steering wheel or dashboard. Gases do not remain in the bag for long, allowing it to deflate after a few seconds.
1 How does the Particle Theory explain the fact that gases are compressible and liquids are not?
2 What is the difference between a pneumatic system and a hydraulic system?
3 What uses exist for pneumatic devices?
4.7 Choosing a Hydraulic or Pneumatic System
Scientists and technologists rely on their observations. The evidence they collect helps them to figure out relationships among variables. From these relationships, scientists can decide what type of scientific principle a new technology should be based on. In this lesson, you are going to have to decide whether a new technology you create should be based on a hydraulic or pneumatic fluid system. To help you make this decision, think about the observations you have made regarding fluid systems.
What do you know?
You know that in fluid systems:
• As the pressure exerted by a fluid increases, it will create a larger force.
• Liquids do not compress and are used in hydraulic systems.
• Gases compress and are used in pneumatic systems.
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Think back to your experiments. What did you find? You found that gases compress and liquids do not. Although both pneumatic and hydraulic systems can transfer forces from one part of a system to another, the compressibility of gases and incompressibility of liquids give the two types of systems different characteristics.
Technologists use these characteristics to decide which system they should use as a basis for their new tools.
What might the different characteristics of pneumatic and hydraulic systems be? What relationships cause these differences?
Characteristics of Hydraulic Systems Characteristics of Pneumatic Systems Liquids do not compress and expand, so
they are:
• very quiet, and
• can deliver a force for an extended time.
Gases compress and expand, so they are:
• very loud, and
• can deliver a short burst of force.
Oils are used as hydraulic fluids.
• Oils do not freeze.
• Oils can become highly viscous in cold temperatures.
• Oils need long warm-up times.
• Oils are flammable.
• Oils have a high cost.
• If a hose breaks, a leak may result in a mess and the machine does not work.
Air is used in pneumatic systems.
• Moisture in the air can freeze.
• Air does not become viscous in cold temperatures.
• Air does not need long warm up times in cold temperatures.
• Air is not flammable.
• Air has no cost.
• If a hose breaks, the pressure may cause the hose to whip dangerously and the machine does not work.
Hydraulics are contained systems.
• They can work under water.
• They do not tend to require cleaning maintenance.
• They do not give off potentially harmful substances.
Pneumatics exhaust air into the environment.
• Most cannot work under water.
• They tend to require cleaning maintenance.
• They may give off potentially harmful exhaust.
Pressurized air gives a pneumatic drill a short impact force to break apart hard surfaces.
A hydraulic system allows a mechanical scrubber to be used under water.
Before You Start...
Imagine you are working for a small company that makes different kinds of toys. These toys can be used by children all over the world because they are fun to play with, and they do not require any special equipment such as batteries. The toys are for a whole range of ages—from babies to young adults.
Work with your partner or small group to make a list of toys that you think children would enjoy, or that you had fun with when you were younger. The only guide is that the toy must not require any electricity.
The Question
How will you create a toy that uses at least one hydraulic or pneumatic device?