## Wednesday, March 31, 2010

### general science#12

#### Distribution of elements on the surface of the earth

 Element Distribution Element Distribution Oxygen 49.85% Silicon 26.03% Aluminium 7.28% Calcium 3.18% Sodium 2.33% Potassium 2.23% Magnesium 2.11% Hydrogen 0.97% Titanium 0.41% Chlorine 0.20% Carbon 0.19% Others 1.00%

#### Metals and their ores

 Substance Ore Substance Ore Calcium Limestone, marble, chalk Mercury Cinnabar Copper Copper pyrites, Cuprite Potassium Carnelite, Saltpetre Cement Limestone and clay Sodium Rock salt, Cryolite Glass Silica and lime stone Thorium Monozite Iodine Sea weeds Titanium Rutile, limenite Iron Hematite, Magnatite, Iron pyrites Uranium Pitchblende Gold Aurite Silver Argentite

#### Metals and their alloys

 Alloy Component Brass Copper, Zinc Bronze Copper, Tin, Zinc Gun metal Copper, Tin, Zinc Duralmin Aluminium, Copper,Magnesium, Manganese Solder Aluminium, Lead, Tin Pewter Lead, Tin

## Notes

Speed is the rate of change of distance
$speed = \frac{distance}{time}$
Velocity is the rate of change of displacement. It signifies both the speed and the direction of movement of an object.
$velocity = \frac{displacement}{time}$
Acceleration is the rate of change of velocity.
$acceleration = \frac{velocity}{time}$
Acceleration due to gravity is the acceleration experienced by an object as it falls freely towards the ground. It is constant throughout the surface of the earth.
$g= 9.8 \frac{m}{s^2}$
Momentum is a measure of the quantity of motion possessed by a body.
$momentum = mass * velocity$
Equations of motion
Let an object be moving for time t at an acceleration a resulting in a displacement s. If the initial velocity of the object is u and the final velocity v, the following equations hold true
$v=u + at$
$s = ut + \frac{at^2}{2}$
$v^2 - u^2 = 2as$
Newton’s laws of motion
First law: A body continues in its state of rest or uniform motion unless compelled to change by an unbalanced force
Second law: A body of mass m under an acceleration a experiences a force F given by $F = ma$
Third law: Whenever a body A exerts a force F on another body B, the second body B exerts force -F on A.

## Questions

1. The universal law of motion was propounded by

1. Kepler
2. Galileo
3. Newton
4. Copernicus
2. The gravitational force with which the Sun attracts the Earth is

1. less than the force with which the Earth attracts the Sun
2. the same as the force with which the Earth attracts the Sun
3. more than the force with which the Earth attracts the Sun
4. constant throughout the year
3. The mass of a body is different from its weight.

1. Mass is variable whereas the weight is constant
2. Mass varies very little at different places whereas weight varies significantly
3. Mass is constant but weight increases from the pole to the equator
4. mass is a measure of quantity of matter whereas weight is a force
4. The weight of a body is

1. same everywhere on the surface of the earth
2. maximum at the poles
3. maximum at the equator
4. more on hills than in plains
5. If a body is taken from the Earth to the Moon,

1. its mass will be different but weight will still be the same
2. both mass and weight will be different
3. mass will be the same but weight will be different
4. mass and weight will both remain unchanged