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Tuesday, March 29, 2011

Fish & Buoyancy

Today let's revise some form 4 topics on Buoyant Force. In SPM, we learned that buoyant force depends on its volume of water displaced. The larger the volume displaced, the greater the buoyant force. Buoyant force also depends on density of the water, i.e greater water density produce greater buoyant force.
Learning physics will be interesting if u are able to blend its concept with nature & things around u. When i was a kid, i loved to keep fish as a pet and guppy was one of my favorites. Fish is very mobile in water. They are able to swim to the surface, stay in the middle of the water or sink to the bottom.

Ok how they did it.. I mean to float and sink?? Basically fish is able to do it through air filled bag called swim bladder. This bladder has nothing to do with its urine product. In fact swim bladder helps most fish to maintain its buoyancy. To swim upward a fish fills the bladder with oxygen through the gills. When the bladder is filled with oxygen, the fish has a greater volume and its bladder is expanded. This displace more water and so it experiences a greater buoyant force.

In order to sink,air is removed from the bladder that causes decrease in its volume. Thus its average weight will be greater greater than buoyant force which then pull it towards ocean floor.

To float at certain level, the bladder is filled with air until it displaces a volume of water to produce a buoyant force that equal to its weight. In this case, the weight & buoyant force are in equilibrium. Thus it stays at that level. The same concept is applied in submarine except submarine needs a ballast tank to increase or decrease its buoyancy by adding or removing sea water inside it.

Wednesday, March 9, 2011

HOW TO BUILT A SOLAR CAR MODEL

BASIC CONSTRUCTION OF THE MODEL CAR

1. The completed model racing car is shown below. The ‘underneath’ view shows the motors fixed top a polystyrene base, held to it by insulation tape. The front plastic wheel has a 2mm axle which is taped to the card base. The sequence / stages involved in the construction of the model car are shown on the pages to follow.






SEQUENCE DRAWING OF MANUFACTURE

1. Cut out the shapes for the card base and bodywork.



2. Shape / form three art straws to the frame of the model car. When folding/bending the straws, place the straws on top of the card base to ensure that the straw frame matches it in size. Then sellotape the art straw frame to the card base.



3. Cut a rectangular slot at the front of the card base, using a craft knife. This must be accurately cut as the front wheel should fit precisely in position. If the rectangle is too large the front wheel will move from side to side when the finished model is tested. This will make the model move in circles rather than a relatively straight line.



4. Solder short red and black wire to the motors. Check that red is soldered to the positive terminal and black to the negative terminal of each motor. Fix the motors on to the polystyrene motor base, using insulation tape.



5. Turn the polystyrene motor base over and connect the red and black wires to the electrical connectors as shown in the diagram opposite. Then connect a further long red and black wires to the opposite side of the connector.



6. Sellotape the motor base to the straw frame/card. Be careful hoe the model car is picked up as it is not a strong structure. Lift the model by the motor base otherwise the model could be damaged.



7. Carefully turn over the model and use insulation tape to fix the axle to the card. Then turn over the model again so that it stands on all four wheels.



8. Cut out the bodywork card and draw a design that reflects the theme of a racing car. The card can be pushed into the art straw frame quite easily. In fact the bodywork can be interchanged so that the model has different bodywork each time it runs/races.





9. Finally connect the solar panels and, if in England, wait for a sunny day. ‘Flick’ the switch and the model car will move either forward of backwards. Switch the wires at the solar panels terminals to alter the direction.

COMPONENTS REQUIRED TO MAKE THE SOLAR POWERED MODEL CAR

A solar powered model racing car can be made quite easily using very basic equipment, tools and materials.

1. A pair of scissors insulation tape, sellotape and a craft knife, for holding some of the components to the straw frame.



2. Two 3 to 6v motors are needed to drive the back wheels and a piece of 2mm compressed polystyrene or PVC. The motors will be taped to the polystyrene using insulation tape




3. Two rubber wheels with a 1.5/2mm hole through the centre. The wheels will be pushed straight on to the shafts of the motors (friction fit).




4.One /two jumbo art straws, 400mm in length. These will be used to make the basic frame of the vehicle.



5. A plastic wheel will be used for the front of the vehicle. A small 2mm steel axle is also required.



6. A line of electrical connectors are used to connect the wires from the motors to the solar panels and ON/OFF switch.





7. A small electrical screw driver, wire cutters, wire strippers, long nose pliers and soldering iron, for working with the electronics aspect of the project.




8. Cheap solar panels (photovoltaic panels). These will provide the electrical power required to drive the model solar car forward.



9. An A3 piece of card with the size of the card base and bodywork clearing marked out. If a number of model solar powered cars are to be made, simply photocopy the as many times as necessary.




10. A range of drawing equipment will be needed to add a design and colour scheme to the bodywork of the model car.

Sunday, March 6, 2011

An Electric current


Figure 1

1. Hi guys...have you ever seen an instrument such as shown in Figure 1 ? What is the name and purpose of this instrument? It is an ammeter. Ammeter is used to measure an electric current.

Figure 2

2. Now look at Figure 2. The reading of the ammeter is 3 Amperes (3A). It shows that the current flow is 3A. What does it mean? It is the indication of the amount of electric charges that flow every second. It is because electric current, I, is the rate of flow of electric charges, I = Q/t, where Q is the amount of electric charges flow in Coulomb (C) and t is the time taken for the electric charges to flow in second (s).

3. The unit of an electric current is Ampere(A) which is equivalent to Coulomb/second

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