GRADE SIX SCIENCE
Hello Boys and Girls, How has your past week been? Have you been revising and revising? Do ensure that you keep working very hard. During this week our country celebrates another year of republican status. (Can you tell how many years?) Do have lots of fun on Thursday and be careful. Did you enjoy doing those exercises last week? Did you get all of them correct? We will continue to look at simple machines.
This week we will look at Inclined Planes, Wedges and Screws.
The Screw
An inclined plane is one of the simplest types of machines. It is really a slanting or sloping surface where one end is higher than the other. A ramp is an inclined plane. The road up a hillside and the slide in a children’s playground area are all inclined planes. The inclined plane is used in many different ways. It is used at loading docks.
Here the load is raised to a certain height using less force than would be required to lift it straight up. The work is easier, but the actual amount done remains the same. Planks at building sites enable wheelbarrows to be raised easily from the ground. There are inclined planes at filling stations, too. The bannister down (or up) a stairway. Can you think of other areas where inclined planes are used?
The screw is a special kind of inclined plane. It is really an inclined plane wrapped around a cylinder. You can easily see this if you cut a piece of paper into the shape of a triangle and brightly colour the long side (which is the inclined plane). Next wind the paper round the pencil in such a way that you can se the coloured inclined plane. Look at the diagrams which follow and it will help you make the model.
The threads of a screw move up in a similar way. Screws have many uses. We can use them to fasten things to wood or even steel to steel. A car jack is a screw. The cutting part of a drill is also a screw. The lid of some jars is a screw. Did you know that some office chairs (swivel chairs) use the principle of the screw? I am sure that you can name other items that are really screws.
Screws are used not only to hold things together but to make things turn, for digging and lifting. No one can really lift a car by himself or herself. The screw, as you can see, usually has a head at one end that contains a specially formed shape that allows it to be turned over, or driven with a tool. Common tools for driving tools include screw drivers and wrenches.
A wedge is simply a triangular tool, often made of metal, wood, stone or plastic. It is thick on one end and tapers to a thin or sharp edge on the other end. Technically it is an inclined plane (or two inclined planes put together to form a triangle) that moves. A wedge may be attached to a handle to make it easier to use. Good examples of wedges are nails, knives, axes and your teeth.
From the above, you will notice that the force applied to the thick end of the wedge overcomes the resistance of the wood. The force is directed downwards, but the wedge directs the force sideways as it drives into the wood.
Wedges have been in use for millions of years. Earlier humans used wedges made of hard rocks and stones to hunt (like spears), cut and trim trees and carve stones. The concept of wedges is also used in jets and modern cars. You will notice that jets, fast cars, speed boats and trains have pointed noses. This helps them cut through the air (air acts as a resistance).
Until next week, goodbye Boys and Girls!