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Wednesday, February 25, 2009

♥ Center Of Gravity

The center of gravity is a geometric property of any object. The center of gravity is the average location of the weight of an object. We can completely describe the motion of any object through space in terms of the translation of the center of gravity of the object from one place to another, and the rotation of the object about its center of gravity if it is free to rotate. If the object is confined to rotate about some other point, like a hinge, we can still describe its motion. In flight, both airplanes and rockets rotate about their centers of gravity. A kite, on the other hand, rotates about the bridle point. But the trim of a kite still depends on the location of the center of gravity relative to the bridle point, because for every object the weight always acts through the center of gravity.

Source: http://www.grc.nasa.gov/WWW/K-12/airplane/cg.html

I AM GRUMPY.
11:48 PM

♥ Center Of Mass

The center of mass of a system of particles is a specific point at which, for many purposes, the system's mass behaves as if it were concentrated. The center of mass is a function only of the positions and masses of the particles that comprise the system. In the case of a rigid body, the position of its center of mass is fixed in relation to the object (but not necessarily in contact with it). In the case of a loose distribution of masses in free space, such as, say, shot from a shotgun, the position of the center of mass is a point in space among them that may not correspond to the position of any individual mass. In the context of an entirely uniform gravitational field, the center of mass is often called the center of gravity — the point where gravity can be said to act.

The center of mass of a body does not always coincide with its intuitive geometric center, and one can exploit this freedom. Engineers try to design a sports car's center of gravity as low as possible to make the car handle better. When high jumpers perform a "Fosbury Flop", they bend their body in such a way that it is possible for the jumper to clear the bar while his or her center of mass does not.The so-called center of gravity frame (a less-preferred term for the center of momentum frame) is an inertial frame defined as the inertial frame in which the center of mass of a system is at rest.

I AM GRUMPY.
11:41 PM

Monday, February 23, 2009

♥ Densest Element On Earth ???


The densest element on earth is osmium. Osmium is a hard, brittle, blue-gray or blue-black transition metal in the platinum family. The density of osmium is 22610 kg⁄m³ (22.61 g⁄cm³), slightly greater than the density of irridium, the second densest element. Osmium is used in alloys with platinum, irridium other platinum and group metals. Osmium is found in nature as an alloy in platinum ore. Alloys of osmium are employed in fountain pen tips, electrical contacts and in other applications where extreme durability and hardness are needed

I AM GRUMPY.
5:14 AM

Sunday, February 22, 2009

♥ About Archimedes ...

Archimedes of Syracuse(c. 287 BC – c. 212 BC) was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Among his advances in physics are the foundations of hydrostatics, statics and the explanation of the principle of the lever. He is credited with designing innovative machines, including siege engines and the screw pump that bears his name. Modern experiments have tested claims that Archimedes designed machines capable of lifting attacking ships out of the water and setting ships on fire using an array of mirrors.

Archimedes is generally considered to be the greatest mathematician of antiquity and one of the greatest of all time.He used the method of exhaustion to calculate the area under the arc of a parabola with the summation of an infinite series, and gave a remarkably accurate approximation of pi.He also defined the spiral bearing his name, formulas for the volumes of surfaces of revolution and an ingenious system for expressing very large numbers.

Archimedes died during the Siege of Syracuse when he was killed by a Roman soldier despite orders that he should not be harmed. Cicero describes visiting the tomb of Archimedes, which was surmounted by a sphere inscribed within a cylinder. Archimedes had proven that the sphere has two thirds of the volume and surface area of the cylinder (including the bases of the latter), and regarded this as the greatest of his mathematical achievements.

Unlike his inventions, the mathematical writings of Archimedes were little known in antiquity. Mathematicians from Alexandria read and quoted him, but the first comprehensive compilation was not made until c. 530 AD by Isidore of Miletus, while commentaries on the works of Archimedes written by Eutocius in the sixth century AD opened them to wider readership for the first time. The relatively few copies of Archimedes' written work that survived through the Middle Ages were an influential source of ideas for scientists during the Renaissance,while the discovery in 1906 of previously unknown works by Archimedes in the Archimedes Palimpsest has provided new insights into how he obtained mathematical results.

I AM GRUMPY.
10:31 PM

♥ Gravity Stronger At The North Pole ???

Question: Why Is The Gravitational Pull Stronger At The North Pole ?

Answer: This is because the earth is very slightly flattened at the poles, so the North and South Poles are a bit closer to the center of the Earth than land on the Equator. And the South Pole is in Antarctica, which is a very high plateau, so the gravity there would be a bit less than that at the North Pole, which is in the middle of a deep ocean.

I AM GRUMPY.
9:49 PM

Friday, February 20, 2009

♥ Parallax error


Question: What is parallax error ?


Answer: Parallax error is when your eye is in the wrong position for viewing.


Question: How can we avoid parallax error ?


Answer: To avoid parallax error, place your eye vertically above the marking that is to be read.


I AM GRUMPY.
11:51 PM

Monday, February 16, 2009

♥ What is Terminal Velocity ?











Aristotle first recognized that falling objects fall at a constant speed. He probably came to this conclusion based on observations of things falling through water. Falling objects have two forces acting on them. The weight , acting downwards, the frictional drag rushing past, which tries to slow the body down. This drag force acts upwards and therefore lessens the acceleration as the body falls. If the body continues to fall, the acceleration will continue to decrease and at a certain speed, the drag force will just balance the weight, and the body will be falling at a constant rate. This rate is called the terminal velocity.

As long as the body is falling with a speed less than the terminal velocity, the weight force is less than the drag force, and the object will continue to accelerate. However, as the object gets close to its terminal velocity, the drag almost balances the weight and the total force on the body is small. and so the acceleration is also small. Thus, the body gradually approaches the terminal velocity.

lab_bronco.jpg (110381 bytes)

The time it takes an object to reach terminal velocity depends on the speed it is travelling at, which depends on its weight. Therefore a light object will reach its terminal velocity pretty soon and requires a shorter distancethen a heavier object. Very heavy objects will reach their terminal velocity if they fall far enough. For example, we calculate the terminal velocity for the average person and find it to be around 80m/s. The a person will have to fall to reach his/her terminal velocity can be approximately judged using these principles. We know that as soon as the person exits the plane(for example, a skysurfer), his/her acceleration would be close to gravitational acceleration, around 9.8 m/s2. We also know however that his/her acceleration would gradually drop to zero as the speed increased toward 80m/s. Therefore, we can approximate that he/she would have to fall a good deal longer than 8 seconds.

I AM GRUMPY.
3:37 AM

Friday, February 13, 2009

♥ How do astronauts pass urine and pass motion in space ?


Space toilets use air flow as water flushes have drawbacks in zero gravity
Adult nappies are used on space walks and during take-off and landing
The lack of gravity on the shuttle and the space station mean a water-flush system is not an option. You don’t need a particularly vivid imagination to see the potential problems.

Instead, on the shuttle, urine and faeces are carried away by rapid flow of air.

The system separates solid and liquid waste. Solids are compressed and remain on-board to be unloaded after landing. Liquids are released into space. Nasa hopes one day to recycle waste productively.


Researchers at the University of Guelph in Canada have said such recycling will be key to tackling any future mission to Mars in order to feed the astronauts.
The air used in the space shuttle’s toilet system has to be filtered to get rid of the smell and bacteria before it is returned to the living area.


On the International Space Station, the fundamental principle is similar. The fan-powered air-flow toilet system stores waste. Urine is sucked up and stored in 20 litre containers which are dumped into the Progress resupply craft. The ship is later ejected into the atmosphere, where it burns up.


For solid waste, a plastic bag covered in holes is placed inside the toilet. Air is sucked through the holes so everything ends up in the bag. The elasticised top closes and the bag is pushed into a metal container. A new bag is popped in for the next visitor. Again the waste heads off to Progress.


Space toilets have come a long way. In the book The Right Stuff and its film adaptation, an astronaut on an early mission feels the need to urinate during a massively delayed take-off. With no facilities provided - and no adult nappies, as used today during take-off and landing - he is eventually allowed to urinate in his suit, causing his sensors to go haywire.

I AM GRUMPY.
5:54 AM

Monday, February 9, 2009

♥ Moment Of A Force

When we push or pull a door, we are applying a force that causes a turning effect to accomplish a task.

This turning effect is called the moment of a force, and is used to make work easier.
The moment of force at a fulcrum or pivot, which is the point of rotation, is defined by the following equation:

Moment of force, M = F X D Moment of force,

M = Force X Perpendicular distance from the fulcrum to the line of action of the force ( N m )

Since the S.I. units for force and distance are newton ( N ) and metre ( m ), the moment of force has a derived unit of newton-metre (N m).

I AM GRUMPY.
5:06 AM

♥ Force And Work

The work done by a force measures the amount of energy being changed from one form to another as the work is done.

The unit of work done is the joule(J). This is also the unit for energy.

Formula: Work done = Force X Distance moved 1 joule = 1 Newton X 1 metre 1J = 1 N m

One joule is the amount of work done when a force of one Newton moves an object by one metre in the direction of the force.

Example: Marie lifts a 5kg mass from the floor and puts it on a table one metre high. What is the work done? Solution: Work done = Force X Distance moved = (5X10)N X 1m = 50 N m = 50 J Therefore, the work done is 50 J.

I AM GRUMPY.
4:42 AM

♥ Liquefaction

Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world.


Liquefaction occurs in saturated soils, that is, soils in which the space between individual particles is completely filled with water. This water exerts a pressure on the soil particles that influences how tightly the particles themselves are pressed together. Prior to an earthquake, the water pressure is relatively low. However, earthquake shaking can cause the water pressure to increase to the point where the soil particles can readily move with respect to each other.

I AM GRUMPY.
4:31 AM

Friday, February 6, 2009

♥ Newton's 3 laws of motion

1st Law:

An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

This law is often called
"the law of inertia".


What does this mean?

This means that there is a natural tendency of objects to keep on doing what they're doing. All objects resist changes in their state of motion. In the absence of an unbalanced force, an object in motion will maintain this state of motion.

2nd Law:

Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

What does this mean?

Everyone unconsiously knows the Second Law. Everyone knows that heavier objects require more force to move the same distance as lighter objects.

3rd Law:

For every action there is an equal and opposite re-action.



What does this mean?

This means that for every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard.

I AM GRUMPY.
11:02 PM

♥ Meniscus


Meniscus, plural: menisci, from the Greek for "crescent", is a curve in the surface of a molecular substance and is produced in response to the surface of the container or another object. It can be either concave or convex. A convex meniscus occurs when the molecules have a stronger attraction to each other than to the container. This may be seen between mercury and glass in barometers. Conversely, a concave meniscus occurs when the molecules of the liquid attract those of the container. This can be seen between water and glass. Capillary action acts on concave menisci to pull the liquid up, and on convex menisci to pull the liquid down

I AM GRUMPY.
10:31 PM

♥ Quicksand


What is Quicksand ?


Quicksand is a mixture of sand and water, or sand and air, that looks solid, but becomes unstable when disturbed by any additional stress. In normal sand, grains are packed tightly together to form a rigid mass, with about 25 to 30 percent of the space (voids) between the grains filled with air or water. Because many sand grains are elongate rather than spherical, loose packing of the grains can produce sand in which voids make up 30 to 70 percent of the mass. This arrangement is similar to a house of cards in that the space between the cards is significantly greater than the space occupied by the cards. The sand collapses, or becomes 'quick,' when additional force from loading, vibration or the upward migration of water overcomes the friction holding the grains together.


Most quicksand occurs in settings where there are natural springs, either at the base of alluvial fans (cone-shaped bodies of sand and gravel formed by rivers flowing from mountains), along riverbanks or on beaches at low tide. In such cases, the loose packing is maintained by the upward movement of water. Quicksand does occur in deserts, but only very rarely: where loosely packed sands occur, such as on the down-wind sides of dunes, the amount of sinking is limited to a few centimeters, because once the air in the voids is expelled the grains are too densely packed to allow further compaction.


What is the best way to get out of quicksand ?




Step1
Remain calm if you step into a patch of quicksand. Panic is your worst enemy. Just remember that quicksand is not like what you see in the movies.


Step2
Shed excess weight. Just as if you were getting ready for a swim, shuck off your pack or remove your heavy jacket.


Step3
Keep as still as possible until your feet touch solid ground. Most patches of quicksand are only knee deep. If you start going deeper than your thighs, lay back so that you will float better on the top of the quicksand.


Step4
Swim out with slow, deliberate motions. This is very hard work! Extracting yourself from a larger patch of quicksand can take hours.


Step5
Work toward the last known bit of solid ground. Sometimes there may be a crust of solid ground over a patch of quicksand, so you may have walked over this before going into the quicksand.


Step6
Pull yourself out. Once you’ve reached solid ground, pull yourself out of the mess.


I AM GRUMPY.
8:31 PM

♥ Why do we need average ?

In mathematics, an average, or central tendency of a data set refers to a measure of the "middle" or "expected" value of the data set. There are many different descriptive statistics that can be chosen as a measurement of the central tendency of the data items. An average is a single value that is meant to typify a list of values. If all the numbers in the list are the same, then this number should be used. If the numbers are not all the same, an easy way to get a representative value from a list is to randomly pick any number from the list. However, the word 'average' is usually reserved for more sophisticated methods that are generally found to be more useful.

I AM GRUMPY.
8:30 PM

♥ Speed

Speed is a rate of progress - it tells us how fast an object is moving.

Equation: Speed = Distance ÷ Time Average speed:

Because speed may vary over the duration of the journey, we use average speed to simplify calculations.

Average speed is the rate at which total distance travelled varies with the total time taken.


I AM GRUMPY.
7:58 PM

♥ Force and Pressure

A force is a push or a pull.

A force change the shape of an object, change the size of an object, make a stationary move, stop a moving object, speed up or slow down a moving object, change the direction of the moving object.

The measure of the amount of force acting on a unit area is known as Pressure.

Formula for calculating pressure: Pressure = Force ÷ Area (pascal) (Newton) (square metre)
[ pa ] [N] [m²]

If the area increases, the force is constant, the pressure will decrease. If the area decreases, the force is constant, the pressure will increase.

I AM GRUMPY.
7:54 PM

♥ N / Kg ??

Question: Why is the measurement of gravity pull on the moon is counted in N/Kg ?

Answer : Weight = mass X gravitational acceleration
[N] = [Kg] X gg
=[N] ÷ [Kg] = N/ Kg

I AM GRUMPY.
7:52 PM

♥ Mass v.s. Weight



Mass is a measure of the amount of matter in a body.

Weight is the measure of the amount of gravitational force acting on a body







I AM GRUMPY.
7:31 PM

♥ Gravitational Force

Weight = mass X gravitational acceleration
[N] [kg]
spring balance
beam balance

On earth= 10 m/s²

On Moon= 1.6 N/kg OR 1.6 m/s^2

Example: Weight( earth ) = 40 kg = 400 N

Weight( moon ) = 40 kg = 64 N

I AM GRUMPY.
7:16 PM

♥ Topic 2

QUESTION: You are given a lenght of copper wire with a small diameter. The only measuring instrument available to you is the metre ruler. Explain how you would measure the diameter of the wire with an acceptable degree of accuracy.

ANSWER: Firstly, twirl the copper wire around a pencil. Nexy, measure the lenght of the pencil. Then, count how many twirls it takes to make the lenght of the pencil and divide it to find out the diameter of the copper wire.

I AM GRUMPY.
7:15 PM

Tuesday, February 3, 2009

♥ Greenwich Meridian Time

What is GMT ?
GMT( Greenwich Meridian Time ) is World Time and the basis of every world time zone which sets the time of day and is at the centre of the time zone map. GMT sets current time or official time around the globe. Most time changes are measured by GMT. Although GMT has been replaced by atomic time (UTC) it is still widely regarded as the correct time for every international time zone.

I AM GRUMPY.
5:30 AM

Monday, February 2, 2009

♥ Converting...

How to change 240 000 square centi-metre into square metre ?
100 cm = 1 metre so 100cm X 100cm = 10 000 square centi-metre. 10 000 square centi-metre is the same as 1m X 1m which equals to 1 square metre. If we want to find 240 000 square centi-metre into square metre, take 240 000 square centi-metre divided by 10 000 square centi-metre that = to 24 square metre.

I AM GRUMPY.
4:47 AM

♥ Density

Today at Physics, i learnt how to find the density of things.

The formula :

Density= mass X volume

I AM GRUMPY.
4:35 AM


♥ theGrumpyToast ;



      theGrumpyToast is very grumpy. Beware, this toast bites.

      Name: Abigail (:
      School: PLMGSS
      Class: 1-2b '09 , 2-2 '10

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