What did you observe when you tried to push the plunger of the syringe while your hand was pressing against its end?

This chapter is a formal assessment task. It will count for 70% of your term mark.

It is a good idea to make a few trial designs before you make the final model. There is a lot to find out, to think about, to plan and to prepare before you can even start with a project. For the next two and a half weeks, you will design and make a mechanical tool. You will design it in such a way that it solves a particular problem.

Work alone, and only at school. Your teacher will assess your work.

Last weekend, there was an accident just outside town. A car lost control, went off the road and toppled over. Two people were trapped inside the crashed car. They were badly injured, but still alive. Because the metal body of the car was bent, the doors could not open.

Figure 1

Figure 2

An ambulance with paramedics arrived to help the trapped people. But the paramedics could not get them out of the crumpled car in time to give them medical treatment or to take them to the hospital. So the two people inside the car died from their injuries.

Incidents like this are very sad. Many peoples' lives could be saved if it was possible to remove them from car wrecks in time to get medical help.

If the paramedics had the Jaws of Life tools with them, they could have cut or bent the car doors open with these tools to remove the injured people. Then they could have given medical help to the injured people, and the story would have had a happier ending.

Figure 3

Figure 4

Figure 5

Week 1

Another way to move objects from a distance (30 minutes)

You will now learn how you can use syringes to make things move. This wil help you to design tools that can be used by rescue workers at accident scenes.

When you worked with levers, you learnt the following:

A push can be made stronger or weaker by using a lever. In other words, a lever can give you a mechanical advantage.

A movement can be made smaller or bigger by using a lever.

The direction of movement can be changed by using a lever.

You can also change and control movement by using syringes.

Figure 6: This is how you should grip a syringe so that you can push the plunger in with your thumb.

Now you do it.

Figure 7: Close the outlet tube tightly with a finger, then try to push the plunger in.

1. What do you feel when you push the plunger now?

2. What do you think prevents the plunger from going all the way in when you push it hard?

3. Do you think there is something in the syringe that you cannot see?

   To compress means to make something smaller. When you pressed the plunger in while keeping the outlet closed, you compressed the air inside the syringe. That means you forced the air molecules to move closer together.

   Figure 8

4. Do you think you can use a syringe to push something without touching it? Try to do it.

   Connect two syringes with a plastic tube, as shown below.

   Figure 9

   Find out whether your can move small objects by pushing one plunger in.

   Figure 10

   A pushing device made with syringes and pipe that is filled with air, is called a pneumatic mechanism. There are also other types of hydraulic mechanisms.

5. What do you feel when you press the plunger in and try to move the pile of books with your pneumatic mechanism?

   When you use a pneumatic pushing device to try to move an object, you cannot press very hard, because only a small force is needed to compress the air. You can only press with a big force once the air is already very much compressed, when the plunger is pressed almost fully in. Do you think the same thing will happen if there is water in the cylinders instead of gas?

   Fill a syringe with water to investigate this.

   Figure 11

   Figure 12

6. Do you think you can compress the water just like you compressed the air? Try it. Describe the difference you notice between using air in the syringe, and water in the syringe.

   A liquid cannot be compressed.

   It is slightly difficult to get the air bubbles out when you fill two connected syringes with water. The pictures on page 88 show us how this can be done.

   Figure 13

   When there is air or other gases in a device like this, it is called a pneumatic mechanism. When there is water or some other liquid like oil in the cylinders and connecting pipe, it is called a hydraulic mechanism.

7. What would give the strongest push with the same two syringes, air or water? How can you investigate this?

    

1. How many books can you put on top of each other and still be able to push it with your pneumatic pushing device?

   Figure 14

2. How many books can you put on top of each other and still be able to push it with your hydraulic pushing device?

3. Why do you think a hydraulic pushing device provides a stronger push than a pneumatic pushing device?

   To experience the difference between pneumatic and hydraulic pushing devices, hold the two plungers of a pushing device in your hands and push the plungers from both sides.

   Figure 15

   Do this while the syringes are filled with air. Also do it while the syringes are filled with water.

4. What difference do you feel between the pneumatic pushing device and the hydraulic pushing device?

5. Explain why pneumatic and hydraulic pushing devices act differently.

More investigations

Figure 16

Suppose the two syringes and the tube are filled with water. If the plunger on the left is pushed in 1 cm, will the plunger on the right move out by 1 cm or not? Explain your answer.

If a heavy object, like a stone or a box filled with sand, is placed next to the plunger on the right, will the object also move by the same distance than you pushed the plunger in on the left? Explain your answer.

Figure 17

Suppose the two syringes and the tube are filled with air, and a heavy object is placed next to the plunger on the right. If the plunger on the left is pushed in 1 cm, will the plunger on the right move out by 1 cm or not? Explain your answer.

Suppose you use a strong stick or metal rod as a lever to move a brick or other heavy object. If the fulcrum is exactly in the middle of the stick, and you push the one end 5 cm, how far will the other end move?

Will the same happen if you use a flexible lever, like your ruler? Explain your answer.

Figure 19

Suppose the two syringes and the tube are filled with water. If the plunger on the left is pushed in 1 cm, will the object on the right move out by 1 cm or not? Explain your answer.

What will be different if the syringes and tube are filled with air instead of water? Explain your answer.

The syringe on the right is thicker than the syringe on the left.

Figure 20

Suppose the two syringes and the tube in Figure 20 are filled with water. If the plunger on the left is pushed in 1 cm, will the plunger on the right move out by 1 cm or not? Explain your answer.

1. In which case below will you need to use the smallest force on the left to move the object on the right?

   Figure 21

2. Do a few experiments to check your answer to the previous question. Write a short report in the space below.

Lebogang says that when you use a thick syringe to "drive" a thin syringe, you lose strength but gain distance. Jaamiah disagrees. She says that you gain both distance and strength.

What do you think, and why do you think so?

Figure 22

In the above diagram, a thin syringe is used to drive a thick syringe. The yellow object will move by a smaller distance than the red plunger, but the force on the yellow object is bigger than the force on the red plunger. The mechanical advantage is "bigger than one". This means that there is indeed a mechanical advantage, but a distance disadvantage.

Figure 23

This diagram shows how a thick syringe is used to drive a thin syringe. The yellow object will move by a bigger distance than the red plunger, but the force on the yellow object is smaller than the force on the red plunger. The mechanical advantage is "smaller than one". This means that there is a mechanical disadvantage, but a distance advantage.

a spreader to pull pieces of metalapart and tear out chunks ofmetal,

a cutter to cut metal,

a combination tool that can cutand spread, and

a ram, that makes largeopenings to free people who aretrapped.

Figure 24

A model is a small version of a real product. It shows how the real product works, but cannot do the work of the real one. A model does not have to be made from the same materials as the real product.

operate to cut or prise open crumpled metal,

work with linked levers,

be attached to a flat piece of card that will act as a base, and

be powered by a hydraulic system.

What problem did the paramedics encounter at the accident scene?

Who will use the rescue tools?

Where will the rescue tools be used?

In what way will the tools help?

Now write the design brief. Use your answers to questions 1 to 4 to help you. Start your paragraph with:

I should design and make a... [4]

Identify the specifications of the solution.

1. What will the tools be used for? (2)

2. What will make the tools work? (2)

3. To what should your model be attached? (1)

Identify the constraints on the materials.

I should use the following materials to build my model: [3]

[Total: 12]

Figure 25

Figure 26: Drawings made by other learners

Figure 27: More drawing made by other learners

Sketch a possible design of the rescue tool. You can make a simple or a difficult model, as long as you do it well. It is fine if your model only demonstrates how the tool will work, even if the model itself does not work.

Think of the different types of Jaws of Life rescue tools. You have to choose and make only one type of rescue tool.

Label your drawing to show the different parts, and what the parts are made of. Also show where the syringes that form the hydraulic system will go.

[Total: 7]

Make a list of all the materials you plan to use to build your model. You have listed them under "specifications" in the previous lesson. Add any other materials that you will be using.

What will you use for pivots? What will you use to attach the model to the backing sheet? And what will you use to attach the syringe to the backing sheet and the lever? [6]

Figure 28: Here are different pivots and ways to attach pieces of cardboard that were used by other learners. Some were bought and some are hand-made.

Make a list of the tools you will use to build your model. A nail to make holes can also be called a tool. [4]

Some tools can be dangerous if they are used incorrectly. Write down a safety rule for one of the tools that you will use. An example of a safety rule is shown on the right. (2)

Order of work. This is the list of the steps you will follow when you make the model. Below are a few steps to start with. Add more of your own. You can also add steps to this plan while you make your model. (3)

Step 1: Draw the shape of the levers on the card.

Step 2: Cut out the card levers.

Step 3: Make a hole for the pivot point/fulcrum.

Step 4: Assemble the hydraulic system using two syringes with different sizes and tubing.

Step 5:

Step 6:

Step 7:

Step 8:

[Total: 15]

2D working drawing of your model. This type of drawing shows you what an object looks like when you look at it straight from the front, back, side, top or the bottom. Drawings like these are useful because they show the dimensions (measurements) of the object accurately.

Have another look at Chapter 2 to refresh your memory about how to make a 2D working drawing.

Make a 2D working drawing showing one view of your rescue tool. Draw the view that shows the most detail of your model.

On your drawing, each part of the tool should be the correct size compared to the other parts.

You don't have to draw your model to scale and you don't have to add dimensions to your drawing.

Figure 29: An "outline block" drawing of a lever system

outline block to work in, on the next page. Look at Figure 29 on the previous page as an example. Your teacher will look at the following things: Tick

Does the drawing have a heading?

Does the heading include the view that the drawing is drawn in, for example the front view?

Is the block drawn by using the horizontal and the vertical measurements of your model?

Is the block correctly drawn using feint lines?

Are the outlines of the device drawn using dark lines?

Are the different parts of the device in proportion as it wouTech1_LG_gr7_ch8_fig19b.tif Figure 30 ld be in the model?

Is the drawing neat?

Assemble your materials and tools.

Draw and cut out your lever.

Put the lever together.

You can choose materials other than those that you planned for the pivot.

Is it made according to your plan?

10

Does it work smoothly?

5

Is the model neat and well-made?

520

Start by drawing the front view of the syringe using thick, dark lines. This outlines the shape of the syringe.

Measure and draw your 45 ° diagonal lines from the corners. They must be light, feint lines, because they are construction lines.

Measure and mark the depth of the syringe construction lines on the projection. Remember to use half of the real measurement.

Draw in the lines at the back. This is called the "rear lines".

Go over all your outlines. They have to be dark lines.

[6]

Figure 30

Things to look at

Tick

Does your drawing have a heading?

Did you start with the construction lines?

Are these feint lines?

Did you project your corners at 45°?

Did you use ½ the depth measurement to find the rear lines?

Did you draw your outlines as dark lines?

Is your drawing neat?