## Free fall

in free fall without air resistance what is the force that causes the constant acc? Is it the object weight ?
And in free fall with air resistance what is the applied force ? Is it the weight of the object and the resistive force is the air resistance? And the net force is the one that causes the acc?

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 Quote by Celluhh in free fall without air resistance what is the force that causes the constant acc? Is it the object weight ?
Yes. Weight is the force exerted by a gravitational field on a mass. But note that the acceleration is never actually constant. As the object gets closer to the source of the gravitational field, the force, and therefore the acceleration, increase.
 And in free fall with air resistance what is the applied force ? Is it the weight of the object and the resistive force is the air resistance? And the net force is the one that causes the acc?
Yes.

 Quote by haruspex Yes. Weight is the force exerted by a gravitational field on a mass. But note that the acceleration is never actually constant. As the object gets closer to the source of the gravitational field, the force, and therefore the acceleration, increase.
Huh? But g is 10m/s !

## Free fall

 Quote by Celluhh Huh? But g is 10m/s !
As you move further away from the Earth's surface, the value of g decreases proportional to 1/distance2. Only at sea level is g ~10m/s2. You do have to be very high though until you notice the difference, for the astronauts in the international space station g is still > 9m/s2.
 Recognitions: Gold Member Science Advisor If you fell all the way to the center of the earth, your acceleration would be zero - although you would have a very respectable velocity.

 Quote by Chronos If you fell all the way to the center of the earth, your acceleration would be zero - although you would have a very respectable velocity.
Ummm ok, i take it that your point is about tha fact that gravitational pull is exerted from the centre of the earth?
 Just to double check if what I assume is correct, for free fall without air resistance, the applied force is the weight, the acceleration is g-10m/s , because for resultant force f=ma and in this case weight is the resultant force as there is no air resistance present, so weight divided by the mass of the object gives us the acceleration due to gravity for free fall , right ?

 Quote by Celluhh Just to double check if what I assume is correct, for free fall without air resistance, the applied force is the weight, the acceleration is g-10m/s , because for resultant force f=ma and in this case weight is the resultant force as there is no air resistance present, so weight divided by the mass of the object gives us the acceleration due to gravity for free fall , right ?
Right. However, note that acceleration is measured in meters per second squared, not meters per second. The value on earth would therefore be 9.8 m/s2.

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 i take it that your point is about tha fact that gravitational pull is exerted from the centre of the earth?
no...only when you are outside the radius of the earth.

In F = ma, when a = g, F = W......so W = mg
 Gravitational pull is definetly exerted from the centre of the Earth. The distances in the equations are measured from the centre of the eARTH...R NOT H !!! Inside the Earth, falling down a mine shaft, the pull is still towards the centre but may not be 9.8m/s^2 "We know much, we understand little."

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