Presented By: Miss N Mark Pitlochry Primary School Educator MECHANISMS

Mechanisms are the parts that make up a machine. Machines are usually made of many simple mechanisms connected together.

Why are mechanisms useful? They can do the following:

Change the speed of movement

Change the direction of Change a small force into MECHANISMS movement a bigger force

Change the type of movement We use mechanisms to make work easier. There are six simple mechanisms:

• Wheel and axle • The lever • Screw • The wedge • The pulley • The inclined plane

Please follow the link below to watch a video about simple machines:

https://www.youtube.com/watch?v=iQu3GY509ZM THE CRANK

A crank is a type of second class lever. It is a simple mechanism that consists of an arm attached on one end to a shaft (or axle) that can turn and on the other end, the arm has a handle or pedal. The purpose of a crank is to change rotary motion into linear motion to do a task. An example of a crank can be seen in a bicycle pedal. Because it is attached at a 90° angle, the crank can pivot in a complete circle around the axle or shaft. At the other end of the crank, the pedal is attached to the lever of the crank at a 90° angle.

When you turn the pedal-crank-system, you increase the turning force of the angle. This gives the system more mechanical advantage (MA) which allows the system to do more work with less effort. The bicycle pedal system is attached to many other parts, including the wheels. As the pedal and crank turn, the axle turns which ultimately turns the wheels and allows the bicycle to move forward. The system is very similar to Another example of this is the winch (pictured). a bicycle pedal, except that there is a cable or This picture on the right shows a hand-operated winch, but rope which is wound there are many types, for example, off-road vehicles use around the axle. If the motorised winches. Winches are used to lift or pull a load. For handle and crank are example, this hand-operated winch might be used to lift a turned, the axle also turns bucket out of a well, whereas the winch of an off-road vehicle and either reels the rope in might be used to pull the vehicle out of a muddy pit. or reels it out. THE PULLEY

A pulley is a mechanism designed to make lifting and lowering heavy loads easier. It consists of a grooved wheel on an axle. The rope or cable fits into the groove and the pulley wheel moves as the rope moves. There are two types of pulley systems – simple (or single) pulleys and compound pulleys.

Simple Pulleys

The simple pulley has one pulley wheel which is attached to a fixed support (such as a beam or frame). The load, attached to one end of the rope, lifts up as the force is applied downwards as the rope is pulled down through the pulley wheel. A simple pulley does not give us any mechanical advantage. This means you need to apply the same amount of force as the load’s weight. It also means that if you want to lift a load 5m off the ground, you will need to pull the rope down 5m as well. We say that the MA = 1.

Compound Pulleys

The compound pulley consists of two or more pulleys. One pulley is usually fixed and the other is movable (which means that it moves as the load moves). A compound pulley allows us to move a heavier load with less effort. It gives us mechanical advantage. In the above system, there are two pulleys (it is called a “double pulley”). This reduces the effort by half. Mechanical advantage is equal to the number of pulleys in the system, so the MA = 2. However, if you want to lift a load 5m off the ground, you have to pull 10m of rope through the pulley. So, you have to pull it twice as far.

In a compound system, as you add pulleys, the effort needed to lift the load decreases, but the distance you need to pull the rope increases. For example, if you had three pulleys, you would need to put in one-third of the effort, but pull the rope three-times the distance you want to lift the load.

Follow the link below to watch a video about pulleys: https://www.youtube.com/watch?v=9T7tGosXM58 MECHANICAL ADVANATGE

Mechanical advantage is the ability of tools or systems to make it easier to do work. It is a measure of how many times a system multiplies the effort you apply. For example, if the MA = 2, then the effort you apply to move the load, is doubled by the system. This means you only have to actually put in half of the effort to do the same amount of work. The greater the mechanical advantage in a particular system, the less effort is needed to perform the task. Mechanical advantage has two effects: It can multiply input forces and it can multiply input distances.

Multiplying input forces

This means that the system is able to double or triple the input force (what you apply to lift a load) so that the output force is much bigger. This is what allows us to lift a very heavy load with very little effort, for example, a compound pulley system. Multiplying input distances

This means that the system is able to double or triple the input distance (the distance you apply to lift the load) so that the output distance is greater. This allows us to move something a small distance, but the system will move it a greater distance, for example, a fishing reel and rod. The fisherman will wind the reel a small distance, but it will pull the line in from a long distance.

Strengthening Structures

There are three main methods used to strengthen or stiffen frame structures: Tubing, Folding and Triangulation. Consider a bicycle. It is a frame structure that incorporates two of the three methods, namely, tubing and triangulation. Consider the structure of the wheels. The spokes and the wheel rim are attached in such a way that they form triangles. This provides a lot of strength as the wheel carries the bulk of the load. Consider also how the frame of the bike forms triangles.

Consider the structure of the actual frame of the bicycle. It is made of tubes of steel or aluminium that have been connected. The spokes are also cylindrical, or tube-like in shape. These two methods of strengthening provide the structure and stability to make it possible for the bike to perform its task.

Consider a tin can. It is a shell structure that has been strengthened by folding. The folds in a can are called corrugations. The corrugations make the structure more rigid, meaning the structure can stand against a greater force than if it was not corrugated. CRANES

A crane is a machine used to lift and lower materials and move them horizontally. It uses one or more simple machines to create mechanical advantage and move loads beyond the normal capability of a human.

Cranes are often used in the transport industry for loading and unloading, in the construction industry for moving materials, and in the manufacturing industry for assembling of heavy equipment. There are different types of cranes. Some cranes are truck mounted, some are self-propelled (can move themselves), and some are assembled onsite on top of a tall tower. Follow the link below to watch a video about cranes:

https://www.youtube.co m/watch?v=RCxFOK6k0 MA The picture on the right shows a “tower crane”. These cranes are used to help us build high buildings. Tower cranes are tall, straight cranes that use ropes, pulleys and winches to help people lift very heavy things, such as bricks and cement. They are made of simple mechanisms all working together. RECYCLING AND IMPACT

Recycling scrap metal

In South Africa we throw away over 570 million tonnes of rubbish each year. Much of our rubbish ends up buried in the ground in massive landfill sites.

This is wasteful because much of the rubbish can be recycled. In fact, scrap metal is not waste, it is worth a lot of money. Scrap metal which has been sorted into metal types is more valuable than unsorted scrap metal.

Recycling scrap metals has many advantages for the environment.

The advantages of using recycled scrap metal rather than ‘new’ iron ore include:

• Savings in energy • Savings in raw materials used • Reduction in air pollution • Reduction in water use • Reduction in water pollution • Reduction in mining wastes

Some scrap metal goes directly to scrap metal dealers, whilst some scrap metal lands in landfill sites. There is a huge demand for scrap metals worldwide. South Africa exports up to 50% of the scrap that it recovers. However, for the scrap metal to be of value, it needs to be separated into 2 piles:

• Magnetic metals (these are mostly iron-based) • Non-magnetic metals

Separating magnetic materials from non-magnetic materials

Magnetic materials are attracted by a magnet, whilst non-magnetic materials are not attracted by a magnet.

Magnetic metals Non-magnetic metals Iron Lead Cobalt Chrome Nickle Zinc steel Copper Aluminium tin This means that if scrap metal is sorted according to whether it is magnetic or non-magnetic, it will be sorted into broad metal types. Case study Please follow the link below to watch a video of a crane sorting scrap metal: The scrap metal dealer’s problem https://www.youtube.com/watch?v=2n When scrap metal arrives at a scrap metal dealer, the Y2i_L68jA magnetic and non-magnetic metals are usually not separated. It would take too long for the metal to be sorted by hand. A magnet can be used to sort the metals, but the problem with using a permanent magnet is that it is difficult to remove the magnetic metals from the magnet. An electromagnet, where the magnetic properties can be switched on and off, is more suitable.

In scrapyards, large electromagnets are hung from cranes and used to lift heavy loads of iron or steel. This works on the principle that iron is attracted by a magnet, but other metals such as copper and aluminium are not.

The electromagnet can thus be used to separate iron and magnetic metals from other metals. ACTIVITY

TECHNOLOGY GRADE 7 TASK 15 ACTIVITY 1. What is a pulley? 2. What is a crank? 3. What class of levers does a crank belong to? 4. State 2 examples of real life items that use cranks. 5. State 2 examples of real life items that use pulleys 6. What is meant by mechanical advantage? 7. Label this diagram using these labels: Shaft or Axle, Crank, Pedal.

8. Define triangulation. 9. State 3 advantages of using recycled scrap metal rather than new iron ore. 10. What is a crane? 11. State FIVE characteristics of cranes. 12. Use the picture of the tower crane below to answer the questions.

a. What do you think the main purpose of the crane is? b. What do the pulleys do? c. The crane needs to lift heavy things from different places on the ground. How does the trolley help people to lift things from different places on the ground? d. Why does the crane need to rotate? e. What stops the crane from falling over when it lifts something? f. Make a list of all of the mechanisms on this crane that help it to lift loads. g. Now make a list of all the parts that hold the crane up, and keep it balanced, so that it can lift things safely. https://www.pitlochryps.co.za/