Fres = ma for atwood fall machine

In summary, two stationary blocks of the same mass are suspended by a massless string over a pulley. The net force on both blocks is 0. If one block is given a downwards velocity through energy transfer, it will start to fall down. This is in agreement with Fres = ma, which allows for constant velocity. However, the block will eventually stop accelerating once the force is released and will continue to move at constant speed until it hits the pulley.
  • #1
aaaa202
1,169
2
Consider two stationary blocks of same mass suspended by a massless string over some kind of pulley. The net force on both of them is clearly 0. Now suppose we somehow gave on of them a downwards velocity by some kind of energy transfer.
Then intuitively the block would start to fall down. But is that in agreement with Fres = ma? Because the net force on both blocks would be zero and thus allow no acceleration. Though of course Fres = ma does allow for a constant velocity. Therefore: Would the block just fall down with same velocity forever?
 
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  • #2
aaaa202 said:
Consider two stationary blocks of same mass suspended by a massless string over some kind of pulley. … of course Fres = ma does allow for a constant velocity. Therefore: Would the block just fall down with same velocity forever?

yup! :biggrin:

(well, until the other one hits the pulley! :wink:)
 
  • #3
Energy cannot be transferred into the system unless work is done on the system, such as by applying a force to one of the blocks, hanging another mass from it, or whacking it with a sledge hammer. As long as that force is maintained, the system will accelerate. When the force is released such as in the sledge hammer case, then there no longer is energy being transferred into the system, no more work is being done on it, no more unbalanced force exists, and yes, per Newton's first law, in the absence of friction, it will continue to move at constant speed well not forever, but at least until the rising block gets caught in the pulley. Edit: as more concisely stated by tiny-Tim, yepp!
 

What is the Atwood Fall Machine?

The Atwood Fall Machine is a simple apparatus used to demonstrate the principles of Newton's second law of motion. It consists of a pulley system with two masses connected by a string, allowing one mass to fall and the other to rise.

What is the equation for the Atwood Fall Machine?

The equation for the Atwood Fall Machine is F = ma, where F represents the net force acting on the system, m is the total mass of the system, and a is the resulting acceleration. This equation is also known as Newton's second law of motion.

How does the Atwood Fall Machine demonstrate Newton's second law?

The Atwood Fall Machine demonstrates Newton's second law by showing that the acceleration of the system is directly proportional to the net force acting on it, and inversely proportional to the mass of the system. As one mass falls, it exerts a force on the other mass, causing it to accelerate in the opposite direction.

What factors can affect the results of the Atwood Fall Machine?

The results of the Atwood Fall Machine can be affected by several factors, including the mass of the system, the angle of the string, and the presence of friction. These factors can change the net force acting on the system and therefore affect the acceleration.

How is the Atwood Fall Machine used in scientific research?

The Atwood Fall Machine is commonly used in physics experiments and demonstrations to study the relationship between force, mass, and acceleration. It can also be used to measure the acceleration due to gravity, as well as to test the effects of different variables on the motion of the system.

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