# Changes

,  16:52, 2 October 2012
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* All freely falling bodies gain same acceleration.

* All freely falling bodies gain same acceleration.
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= Free fall and acceleration due to gravity =
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<br>
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=== Free fall and acceleration due to gravity ===

A freely falling body undergoes acceleration. This acceleration is caused by the gravitational force exerted by the larger mass of the Earth. This is referred to as acceleration due to gravity. The Earth also undergoes an acceleration due to the gravitational force exerted by the object. We do not notice it because of the mass of the Earth.

A freely falling body undergoes acceleration. This acceleration is caused by the gravitational force exerted by the larger mass of the Earth. This is referred to as acceleration due to gravity. The Earth also undergoes an acceleration due to the gravitational force exerted by the object. We do not notice it because of the mass of the Earth.
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An object that is allowed to fall freely will, if the effects of air resistance are ignored, gather speed (accelerate) at a rate of about 9.8 m/s2. If dropped from rest, it will have fallen 4.9 m and be traveling at a speed of 9.8 m/s after 1 second. After 2 seconds, it will have fallen a further 14.7 m and be traveling at 19.6 m/s. After 3 seconds, it will have fallen a further 24.5 m and be traveling at 29.4 m/s.

An object that is allowed to fall freely will, if the effects of air resistance are ignored, gather speed (accelerate) at a rate of about 9.8 m/s2. If dropped from rest, it will have fallen 4.9 m and be traveling at a speed of 9.8 m/s after 1 second. After 2 seconds, it will have fallen a further 14.7 m and be traveling at 19.6 m/s. After 3 seconds, it will have fallen a further 24.5 m and be traveling at 29.4 m/s.
Variation of 'g' at various places on Earth
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<br><br>
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'''Variation of 'g' at various places on Earth'''

The value of “g” varies according to the effect of the Earth's rotation. If we have a mass hanging in equilibrium from a spring balance at the North Pole, there are two forces acting on the mass, Fg (= mg) and “w” which is the force with which the spring will pull on the mass. An equal and opposite force “w” acts on the spring downwards and this “w” will be read as the weight of the object.

The value of “g” varies according to the effect of the Earth's rotation. If we have a mass hanging in equilibrium from a spring balance at the North Pole, there are two forces acting on the mass, Fg (= mg) and “w” which is the force with which the spring will pull on the mass. An equal and opposite force “w” acts on the spring downwards and this “w” will be read as the weight of the object.
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Please see section on Additional Information for details of difference in “g”.

Please see section on Additional Information for details of difference in “g”.
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Variation due to the shape of the Earth
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'''Variation due to the shape of the Earth'''

When the Earth was formed it was still molten. Due to the rotation, more mass moved towards the centre. This has resulted in the Earth being flatter at the poles and fatter at the equator. There is a difference of about 20 km in the distance from the centre at the equator and the poles. Therefore, an object closer to the equator will have a higher velocity and therefore, higher centripetal acceleration. This will result in a difference in the acceleration due to gravity.

When the Earth was formed it was still molten. Due to the rotation, more mass moved towards the centre. This has resulted in the Earth being flatter at the poles and fatter at the equator. There is a difference of about 20 km in the distance from the centre at the equator and the poles. Therefore, an object closer to the equator will have a higher velocity and therefore, higher centripetal acceleration. This will result in a difference in the acceleration due to gravity.
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If the Earth had no atmosphere, an object dropped from a great height would keep accelerating at a rate of 9.8 m/s2 until it hit the ground. For example, if a person fell from an aircraft at an altitude of 10,000 m, they would be travelling at about 442 m/s (1500 km/ hr) by the time they landed. In practice, this doesn't happen because of air resistance. The faster an object falls, the greater is the air resistance (called air drag) acting on it. Air drag depends on the surface area of the falling object and the speed.

If the Earth had no atmosphere, an object dropped from a great height would keep accelerating at a rate of 9.8 m/s2 until it hit the ground. For example, if a person fell from an aircraft at an altitude of 10,000 m, they would be travelling at about 442 m/s (1500 km/ hr) by the time they landed. In practice, this doesn't happen because of air resistance. The faster an object falls, the greater is the air resistance (called air drag) acting on it. Air drag depends on the surface area of the falling object and the speed.
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At a certain velocity, known as the terminal velocity, the downward force of gravity is balanced out by the upward force of air resistance and there is no further acceleration. And it continues to move at the same terminal velocity till it reaches the ground.
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At a certain velocity, known as the terminal velocity, the downward force of gravity is balanced out by the upward force of air resistance and there is no further acceleration. And it continues to move at the same terminal velocity till it reaches the ground.<br><br>
The effect of air resistance
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'''The effect of air resistance'''
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If there were no atmosphere, all objects would fall at the same rate. This happens, for example, on the Moon. In one of the most memorable moments of the space program, David Scott, commander of the Apollo 15 mission, standing on the Moon's surface, dropped two objects – a geological hammer and a falcon's feather (the Apollo 15 lunar module was called Falcon) – at the same time from the same height. The feather didn't drift down, meanderingly, as it would have done on Earth. Instead, in the airless vacuum of space, it fell straight, without a flutter, keeping pace with the hammer and reaching the lunar surface at the same instant.
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If there were no atmosphere, all objects would fall at the same rate. This happens, for example, on the Moon. In one of the most memorable moments of the space program, David Scott, commander of the Apollo 15 mission, standing on the Moon's surface, dropped two objects – a geological hammer and a falcon's feather (the Apollo 15 lunar module was called Falcon) – at the same time from the same height. The feather didn't drift down, meanderingly, as it would have done on Earth. Instead, in the airless vacuum of space, it fell straight, without a flutter, keeping pace with the hammer and reaching the lunar surface at the same instant.<br><br>
Variance of “g” on Earth
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'''Variance of “g” on Earth'''

In the case of the Earth, g comes out to be approximately 9.8 m/s2 (32 ft/s2), though the exact value depends on location because of two main factors: the Earth's rotation and the Earth's equatorial bulge. We saw that the value of “g” depends on the mass of the Earth and the distance from the centre. At a distance of twice the radius of the Earth, the value of “g” drops to 2.45 m/s2.

In the case of the Earth, g comes out to be approximately 9.8 m/s2 (32 ft/s2), though the exact value depends on location because of two main factors: the Earth's rotation and the Earth's equatorial bulge. We saw that the value of “g” depends on the mass of the Earth and the distance from the centre. At a distance of twice the radius of the Earth, the value of “g” drops to 2.45 m/s2.
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