How can I explain how air resistance damps a pendulum's motion

In summary, air resistance affects the amplitude of a pendulum by causing a damped oscillation over time. This is due to the conservation of energy, where collisions between the pendulum and gas particles result in a transfer of energy, leading to a decrease in velocity and amplitude over time. The explanation for this phenomenon can also be related to the concept of entropy.
  • #1
JamieGreggary
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Basically I have an experiment which involves attaching circular discs of varying radius to a pendulum, monitoring how its amplitude varies with time.

In my write up I need to include an explanation of how air resistance causes a damped oscillation over time. So far I have written:

Air resistance works by the bombardment of gas particles on the circular disc. These collisions cause a change in the gas particles momentum, and hence a force exerted in the opposite direction to the motion of the circular disc. As a result of this, the velocity of the pendulum decreases and energy in the system is lost. This loss of energy means that the pendulum will have insufficient energy to reach the same amplitude as on its last peak, and as a result the amplitude diminishes over time.

I'm not too sure if this explanation is correct (see below of alternative idea). It is also incredibly brief, and am struggling to find inspiration on how else I could explain it/other ideas to include.

Due to the conservation of momentum, when the moving pendulum collides with the almost stationary particles, energy is transferred from the pendulum and onto the particle. This results in the loss of the pendulums momentum and velocity, and an increase in the particles momentum and velocity.

^ Then I'd add the last sentence of the first idea to this - but again, I'm not sure which of the explanations is correct (if any)

Thanks for any help guys!
 
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  • #2
It makes more sense to me to deal in terms of energy rather than momentum here. Clearly both are true, but the question which could be asked is why the process only works in the one direction. If you want to cover that you'd need to go into a discussion of entropy.
 

FAQ: How can I explain how air resistance damps a pendulum's motion

1. How does air resistance affect a pendulum's motion?

Air resistance is a force that acts in the opposite direction of motion for objects moving through the air. For a pendulum, air resistance causes it to slow down and eventually come to a stop due to the drag force it experiences.

2. Why does a pendulum's motion eventually stop due to air resistance?

As a pendulum swings back and forth, it is constantly moving through the air which creates drag. This drag force acts in the opposite direction of the pendulum's motion, causing it to lose energy and slow down until it eventually comes to a stop.

3. How does the shape of a pendulum affect the amount of air resistance it experiences?

The shape of a pendulum can greatly impact the amount of air resistance it experiences. A more streamlined and aerodynamic shape will experience less air resistance compared to a bulky or irregularly shaped pendulum.

4. Can air resistance be reduced to prevent a pendulum's motion from slowing down?

While it is not possible to completely eliminate air resistance, it can be reduced by changing the shape or material of the pendulum. A more streamlined shape or a smoother surface can help reduce the drag force acting on the pendulum.

5. How does air resistance affect the period of a pendulum?

Air resistance does not directly affect the period of a pendulum, which is the time it takes for one full swing. However, as air resistance slows down the pendulum's motion, the period will also increase as the pendulum takes longer to complete each swing.

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