To all grade 9 learners • Please see TECHNOLOGY WORK TERM 2 ... - Roodie

[Pages:48]To all grade 9 learners ? Please see TECHNOLOGY WORK TERM 2 document . ? Rewrite the document in your workbook. ? Start with the keywords on the last page and then start from the first page. ? Please redraw easy pictures or print pictures if possible. (will print some of the picture when school start again). Please leave space available in book for the pictures if you are unable to draw or print. ? Please read through the power point and do all activities in the power point given. Please be safe and work hard. See you when school starts again. Miss Bekker

Term 2 : Pneumatic systems and Hydraulic systems.

Pneumatic systems:

- Use compressed air to make mechanisms work or move. - Compressed air is the ordinary air that you breathe which is forced into a small but

restricted space. - Compressed air is under pressure because it is forced into a confined space. - Pneumatic systems transmit force and movement over long and short distances with

very little friction. - Pneumatic systems control movement in small appliances such as dental drills and

are also used in tyre fitment bays to tighten or undo wheel nuts.

Air is Compressible:

(This describes whether it is possible to force an object into a smaller space than it normally occupies. For example, a sponge is compressiblebecause it can be squeezed into a smaller size).

Liquid is Incompressible:

(The opposite to compressible. When a "squeezing" force is applied to an object, it does not change to a smaller size. Liquid, for example hydraulic fluid, possesses this physical property).

Hydraulic systems:

- Are used widely to transmit power. - Hydraulic systems use liquid to transfer force from one point to another. - Liquids are incompressible. - Hydraulic systems use liquid to create a mechanical advantage.

- A well-constructed hydraulic system has the following advantages: 1. Fluids or liquids cannot break. 2. Mechanisms do not wear out. 3. It can provide smooth action without any vibration. 4. It is not affected by change of load. 5. Low cost to operate.

- Principles of hydraulics A liquid or fluid has no shape of its own and changes shape according to its container. A liquid transmits the pressure applied to it in all directions and therefore provides great increase in work force.

The syringe on which you push the plunger in is called the input or master cylinder of the system. The syringe that is moved is called the output or slave cylinder of the system.

If the output cylinder in a simple hydraulic system is wider than the input cylinder, the output distance is smaller than the input distance, but the output force is bigger than the input force.

output

input

Hydraulic car jack:

? A device that is used to lift cars so that wheels can be changed is called a jack. ? A jack provides a mechanical advantage. ? A bottle jack has a hydraulic pushrod system inside, that provides a mechanical

advantage. ? When the blue input cylinder is pushed down by some distance, the red output

cylinder moves up with a bigger force, but by a much smaller distance.

1. Handle.(pump mechanism) 2. Lever mechanism 3. Input piston 4. Release screw

5. Reservoir 6. Output piston 7. One way valve 8. Spring

Pascal's principle

When we apply pressure anywhere to a fluid in a closed container, the force is transmitted equally in all directions. This happens throughout the fluid and onto the walls of the container.

Pulleys and controllers

? WHAT IS A PULLEY? A pulley is a simple machine made with a rope, belt or chain wrapped around a wheel. The pulley is usually used to lift a heavy object (load).

? WHAT DOES A PULLEY DO? A pulley changes the direction of the force, making it easier to lift things

? When two surfaces rub against each other, there are forces that act on the materials, and parts of the materials may break.

? The forces that act when materials rub against each other are called friction forces. ? On a cold day you sometimes rub your hands against each other to warm them up. ? The warmth comes from the friction forces. ? To prevent friction from harming a rope that is used to change the direction of

pulling an object, one may let the rope run over a wheel that is called a pulley.

Different types of pulley systems:

Single wheel fixed pulley Single wheel moveable pulley Compound pulley / combined pulley

A pulley

The man uses a pulley to lift the sack

The system that the man in the Figure above uses is called a single wheel fixed pulley system. Its purpose is to change the direction of pull, but it does not give a mechanical advantage.

The man cannot lift the sack from the ground up to the branch with one pull. He needs to make a plan so that the sack will not drop down again while he shifts his hands to get ready for another pull. The diagram on the right shows a device called a cam cleat. If you pull the rope upwards, the cams will close in on the rope and prevent it from passing through. If the rope is pulled downwards, the cams are pushed apart and the rope can pass through easily.

Devices like a cleat, or the valves allow certain movements, but prevent other movements. Devices such as these are called control devices.

A single fixed pulley:

A cam cleat

? A single pulley changes the direction of the lifting force. For example, if you are lifting a heavy object with a single pulley anchored to the ceiling, you can pull down on the rope to lift the object instead of pushing up. The same amount of effort is needed as without a pulley, but it feels easier because you are pulling down.

? Has one wheel and is fixed to a wall, beam, bar. ? The wheel is fixed, which means that it does not move. ? Use gravity or weight to apply the force that you need to raise the object on the

other end of the pulley rope. ? If the object you are trying to lift is heavier than you, you need to put in more effort

to raise it. ? A fixed pulley therefore does not give you any mechanical advantage. ? It change the direction of the pull. ? For example: you pull down on a rope to lift something up. ? MA = 0

? The fixed pulley when attached to an unmovable object e.g. a ceiling or wall, acts as a first class lever with the fulcrum being located at the axis but with a minor change, the bar becomes a rope.

? The advantage of the fixed pulley is that you do not have to pull or push the pulley up and down.

? The disadvantage is that you have to apply more effort than the load

Single wheel moveable pulley: ? Change the direction of pull in a slightly different way . ? MA > 0 ? A movable pulley is a pulley that moves with the load. ? The movable pulley allows the effort to be less than the weight of the load. The movable pulley also acts as a second class lever. The load is between the fulcrum and the effort. ? The main advantage of a movable pulley is that you use less effort to pull the load. ? The main disadvantage of a movable pulley is that you have to pull or push the pulley up or down.

A combined / compound pulley: ? A combined pulley makes life easier as the effort needed to lift the load is less than half the weight of the load. ? The main advantage of this pulley is that the amount of effort is less than half of the load. ? The main disadvantage is it travels a very long distance.

GEARS

TYPES OF GEARS A gear is a toothed wheel having a special tooth shape or profile enabling it to mesh smoothly with other gears. These are used to transmit power from one shaft to another shaft in closed contact. These gears are classified according to location of the shaft, position of the tooth and types of tooth shapes. The follow gears are mainly used: 1. Spur gear 2. Helical gear 3. Bevel gear 4. Worm gear 5. Rack and Pinion

1) Spur gear ? These are also called as spur gears the gears having tooth in straight & parallel to the

axis of the shaft. ? These gears are used to transmit the power in gearbox of automobiles. ? This type of gears are used to transmit more power.

An idler gear is a gear placed between two others to transfer motion without a change in direction.

The purpose of the idler gear is to synchronise. When a idler gear is inserted into a gear system the bigger and smaller gears turn

in the same direction at the same time.

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