Does Using a Pulley Affect Acceleration in a Frictionless System?

In summary, adding a mass to the rope will decrease the net force on the original block due to the tension created in the rope. The pulley does not factor into the force equation as it only changes the direction of the tension force. The decrease in net force is not due to friction, but rather the weight of the added block. To better understand the situation, a force/free-body diagram can be helpful. Starting with a simpler problem, such as tilting the table and placing the pulley at the end, can aid in solving the overall problem.
  • #1
just.karl
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With a mass on a frictionless surface connected to a string that is sent over and down to a mass. Would that increase or decrease the acceleration compared to the equation, a=g(m). I'm just stumped on how to think of this. The pulley is not included in the equation but how would I figure out the difference?
 
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  • #2
The extra mass attached to the rope will cause a tension in the rope correct? How does this tension affect the net force on the original block?
 
  • #3
It would decrease the net force on the original block, correct? But would it be just because of friction or is it something more complicated than that?
 
  • #4
Yes, the net force would decrease but not for the reason you are suggesting.

Consider the pulley to be frictionless. It's not the pulley that is decreasing the force on the block, but the weight of the second block that is added. The weight of the block causes a tension in the rope, and the rope thus pulls up on the first block, decreasing the net force on the first block. All the pulley really does is change the direction of the tension force so it pulls up on the block. This is why the pulley doesn't factor into the force equation, since it doesn't create any new forces.

(Of course, in reality, there is some friction in the pulley which will decrease the net force on the block, but it is not the primary cause of the decrease.)

Does this make sense? I suggest drawing a force/free-body diagram of the situation. It may help you visualize what's happening.
 
  • #5
make it as simple as possible first

just.karl said:
With a mass on a frictionless surface connected to a string that is sent over and down to a mass. Would that increase or decrease the acceleration compared to the equation, a=g(m).

I assume by "frictionless surface", you mean a horizontal one, like a really smooth table?

Try an easier problem first: tilt the table, and put the pulley on the end of the table, so that the string always stays in the same direction.

Can you solve that problem?
 

FAQ: Does Using a Pulley Affect Acceleration in a Frictionless System?

1. How do pulleys affect acceleration?

Pulleys can either increase or decrease the acceleration of an object, depending on the arrangement of the pulleys. A single pulley can change the direction of the force applied, but does not affect the magnitude of the acceleration. However, a system of pulleys, such as a block and tackle, can increase the force applied to an object, resulting in a greater acceleration.

2. What is the relationship between the number of pulleys and acceleration?

The more pulleys in a system, the greater the mechanical advantage and the greater the potential for acceleration. However, the actual acceleration will depend on the friction and weight of the pulleys themselves, as well as the weight of the object being moved.

3. Can a pulley system increase the acceleration of an object beyond its natural acceleration due to gravity?

No, a pulley system cannot increase the acceleration of an object beyond its natural acceleration due to gravity. However, it can make it easier to lift or move the object by increasing the force applied.

4. How does the angle of the rope or cable affect the acceleration in a pulley system?

The angle of the rope or cable affects the acceleration by changing the direction of the force applied. As the angle increases, the horizontal component of the force decreases, resulting in a decrease in acceleration. This is why it is more efficient to have a vertical rope or cable in a pulley system.

5. How does friction affect the acceleration in a pulley system?

Friction in a pulley system can decrease the acceleration by absorbing some of the applied force. This is why it is important to minimize friction by using smooth and well-lubricated pulleys, as well as minimizing the weight of the pulleys themselves.

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