Physics Question.
Discussion
Terminal Velocity.
Putting air resistance to one side, if i were in an aircraft and fired a gun straight down towards the earths surface, would Terminal Velocity act against the bullet to slow it down to 120/140mph? If so what governs it? Why would gravity, a constant force pulling the bullet downwards act in this way?
Putting air resistance to one side, if i were in an aircraft and fired a gun straight down towards the earths surface, would Terminal Velocity act against the bullet to slow it down to 120/140mph? If so what governs it? Why would gravity, a constant force pulling the bullet downwards act in this way?
Thinking back to my A-level physics I'd say that terminal velocity is for a falling object acted on by gravity alone, not one to which thrust is applied so in the absence of air or other friction the bullet would reach a speed according to the initial force applied and then stay there, however if the tube went all the way through the earth to the other side after passing the centre of gravity the bullet would gradually slow down and stop and be pulled back again and here, as it's just gravity pulling, it would reach 9.8m/s and stay at that speed.
humpbackmaniac said:
Terminal Velocity.
Putting air resistance to one side, if i were in an aircraft and fired a gun straight down towards the earths surface, would Terminal Velocity act against the bullet to slow it down to 120/140mph? If so what governs it? Why would gravity, a constant force pulling the bullet downwards act in this way?
Air resistance would gradually slow the bullet down to a terminal velocity.
Terminal velocity is CAUSED by air resistance. An object falling under gravity alone will continue to accelerate until it impacts the surface of the body attracting it.
As an example, when Joe Kittinger jumped out of a balloon in 1960 at a height of 120,000 feet, his velocity actually went up to over 700 mph until denser air slowed him down at lower levels to the more normal 120 mph.
As an example, when Joe Kittinger jumped out of a balloon in 1960 at a height of 120,000 feet, his velocity actually went up to over 700 mph until denser air slowed him down at lower levels to the more normal 120 mph.
Carrera2 said:
it would reach 9.8m/s and stay at that speed.
Nope - in a vacuum it would fall at 9.8m/s/s and stay at that acceleration.
>> Edited by Carrera2 on Thursday 16th February 08:58
No that would imply it carries on accelerating so would ultimately reach the speed of light. When the astronauts dropped the feather and the hammer or when that fellow dropped the two differing weight cannon balls they reached 9.8m/s and stopped at that speed.
Yugguy said:
it would reach 9.8m/s and stay at that speed.
Nope - in a vacuum it would fall at 9.8m/s/s and stay at that acceleration.
>> Edited by Carrera2 on Thursday 16th February 08:58
No that would imply it carries on accelerating so would ultimately reach the speed of light. When the astronauts dropped the feather and the hammer or when that fellow dropped the two differing weight cannon balls they reached 9.8m/s and stopped at that speed.
I think you're getting confused between constant velocity and constant acceleration.
In your example the items were dropped in a vacuum and had a constant acceleration of 9.81m/s/s.
Yugguy said:
it would reach 9.8m/s and stay at that speed.
Nope - in a vacuum it would fall at 9.8m/s/s and stay at that acceleration.
>> Edited by Carrera2 on Thursday 16th February 08:58
No that would imply it carries on accelerating so would ultimately reach the speed of light. When the astronauts dropped the feather and the hammer or when that fellow dropped the two differing weight cannon balls they reached 9.8m/s and stopped at that speed.
Utter bollox. IQ of 163? don't make me laugh.
humpbackmaniac said:
How can just air resistance cause such a constant outcome? A ball bearing is dense and very aerodynamic, a piano is neither, but is heavy, if dropped from a hot airballoon both stop accelerating at 9.8m/s.
But they don't, and in the absence of some sort of fluid drag they continue to accellerate until they hit the ground.
humpbackmaniac said:
How can just air resistance cause such a constant outcome? A ball bearing is dense and very aerodynamic, a piano is neither, but is heavy, if dropped from a hot airballoon both stop accelerating at 9.8m/s.
(discounting why and how anyone would have a piano in a hot airballoon)
Gravity's 'pull' is 9.81m/s/s on ANY body. Air resistance is the normal opposite force on this and so in your case the ball bearing would fall quicker.
9.8m/s is a bollox figure for velocity - it's just someone getting confused with the 9.8m/s/s acceleration constant, thats all.
If you drop an object from a baloon in the earth's atmosphere it will continue accelerating at a rate of 9.81 m/s/s until this accelerative force is counterbalanced by the decelerative force of air resistance (squares with speed). Then the object has reached a steady state and is at its terminal velocity.
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