[Some Science Facts]Target Naib Tehsildar

When there is no air, the acceleration of an object under free fall is independent of its mass.

Automobiles are streamlined in shape to reduce air resistance and improve fuel consumption.

When an object is thrown vertically upward, the maximum height attained by it is proportional to square of its initial velocity.

h = u²/2g

The time taken by a body thrown up to reach maximum height is called its time of ascent.

t = u/g

Time of flight = time of ascent + time of descent

                     = u/g  + u/g    = 2u/g

Centripetal force is the force that is directed toward the center of an orbital path/spinning object which keeps the revolving object in its orbit. This is in opposition to the "centrifugal force" - a kind of fictitious force that appears to try to pull the object away from the center of the orbit (due to inertia).

Both Centripetal Force and Centrifugal Force play role in a Washing Machine.

Q. Why wheel of an automobile spins in mud?

Ans.  because the centripetal force is not enough to hold the mud on tyre.

Gravitational force between a satellite and the earth acts as a centripetal force, keeping the satellite in orbit.

Centrifugal force is in opposite direction to Centripetal force. On earth, it is minimum at poles and maximum at equator.

Cream from milk is separated by centrifuges in dairy separators.

Kepler’s First law (Law of orbits)

Each planet moves around the sun in an elliptical orbit with the sun at one of its foci.

Second law (Law of areas)

As the planet moves in its orbit, a line drawn from the sun to the planet sweeps out equal area in equal interval of time.

Third law (Law of periods)

T² ∝ R³

Speed of the satellite: -

𝒗²= rg

Thus speed of an artificial satellite does NOT depend upon its mass.

Escape velocity = 11.2 km/sec

Equator or the places near to equator are found suitable for launching the satellites.

Geostationary Orbit (GEO): -

The orbit is circular.

Period of revolution is equal to period of rotation of earth.

The orbit is in equatorial plane.

Geosynchronous Orbit: -

The orbit is NOT circular.

The orbit is NOT in equatorial plane.

The height of the geostationary orbit is 35786 kilometers above earth.

A minimum of three satellites are needed to cover the entire earth- Arthur C. Clarke

Polar orbits are useful in earth mapping.

GEO orbits are helpful in communication.

Frozen orbit is a Sun-synchronous orbit in which the precession of the orbital plane around the polar axis of the Earth caused by the oblateness of the Earth is utilized to the benefit of the mission by choosing correct orbital parameters.

Surface tension of a liquid is defined as the tangential force per unit length acting at right angles on an imaginary line drawn on the surface of the liquid. It’s unit is Newton per Metre.

Any moving liquid has three kinds of energies:

1. Kinetic energy by virtue of its motion

2. Potential energy by virtue of its position

3. Pressure energy when it is subject to pressure

Q. How storms blow off the roofs?

Ans. Due to strong wind, storm or cyclone, the roofs are blown off. When a strong wind blows over the roof, there is lowering of pressure on the roof. As the pressure on the bottom side of the roof is higher, roofs are easily blown off without damaging the walls of the building.

The boiling point of a liquid is lowered under reduced pressure and increased under increased pressure.

Humidity is measured in kg/m³.

Due to change of medium, the phase velocity of the wave is changed but its frequency remains constant.

Periscope is used in the submarines to see objects above the surface of water.

Fibre optics technique is used to destroy tumours in solid organ like liver.

In humans, the refractive power of the cornea is approximately 43 dioptres.

Bifocal lens was invented by Benjamin Franklin.

Short-sightedness or Myopia defect is corrected by wearing glasses with a concave lens.

Long sightedness (or) Hypermetropia defect is corrected by wearing glasses with a convex lens.

The colours of the spectrum of white light are violet, indigo, blue, green, yellow, orange and red (VIBGYOR). The red is deviated least and the violet most.

Q. Why the fruits fall down when a branch of a fruit tree is shaken.

Ans. Because the branch comes in motion and the fruits tend to remain at rest. Hence, they get detached.

Q. Why the coin remains at the same place on the table when a smooth paper having a coin on it placed on a table is suddenly drawn.

Ans. Due to inertia of rest

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