The effects of gravity on a pendulum

In summary, the physics teacher is correct, gravity has nothing to do with a pendulum coming to rest.
  • #1
onestarburns
12
0
Forgive me if this is anything but trivial, but my physics teacher said in his lecture the other day that gravity has nothing to do with a pendulum coming to rest? how could this be? according to him, the reason for the pendulum coming to rest is air, but when i inquired about puting one in a vacum, he said that friction would then play a role. am i wrong to feel that this may be false? and if my physics instructer is correct, could you help me understand why gravity plays no role in the object coming to rest. thanks
james
 
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  • #2
He's right.

Gravity plays no part in the pendulum coming to rest because no energy is lost to it.

If you lift a weight up to the top of a hill, and then let it drop, the amount of potential energy you give it by lifting it up is exactly the same as the amount of energy it loses whilst being returned to the bottom.

The same principle applies to a pendulum; once it reaches the bottom of its stroke, all the energy it had at the top has been converted to kinetic energy, and could thus (ideally) carry on back to the top of its stroke again.

Your teacher is correct in stating that the forces acting against its movement are friction (in the bearing mechanism) and air resistance.
 
  • #3
Your teacher is absolutely right. Gravity has everything to do with where the pendulum comes to rest but nothing to do with the fact that it does come to rest. Consider what would happen if there were no friction in the pivot (which I think is more important than air resistance- apparently your teacher oils his pendulums better than I do!) and plenty of gravity. The pendulum would move back and forth forever without coming to rest. Consider, on the other hand, a pendulum with no gravity but friction and air resistance. The pendulum would not, even from the start, swing back and forth but go "round and round". Eventually, however, friction and air resistance would "steal" all of the energy and the pendulum would come to a stop.

I said, above, that gravity has everything to do with where the pendulum comes to rest. Obviously, with gravity, the pendulum will come to rest at its lowest point. Without gravity the pendulum will come to rest where ever it happened to be when its energy ran out.
 
  • #4
Gravity is one of the forces that makes a pendulum go - the other is the initial kick to get it started. If there was no friction (or air resistance) it would oscillate forever.

Specifically, gravity pulls the pendulem to the bottom of its arc, where its velocity is enough to keep it going to the top of its arc, where it comes to a stop and turns back down. The arc length will be constant in the absense of friction or air resistance.
 
  • #5
thanks

once again you guys have helped a great deal. thanks alot, and i must say it is great to have such an awsome sorce of information from such a wonderful community.
thanks: james
 

FAQ: The effects of gravity on a pendulum

1. How does gravity affect the motion of a pendulum?

Gravity is the force that pulls objects towards each other. In the case of a pendulum, gravity is what causes the pendulum to swing back and forth. As the pendulum moves, gravity pulls it down towards the center of the earth. This force is what gives the pendulum its energy and keeps it in motion.

2. Does the length of a pendulum affect its swing due to gravity?

Yes, the length of a pendulum does affect its swing due to gravity. The longer the pendulum, the slower its swing will be. This is because a longer pendulum has a greater distance to travel and therefore takes more time to complete each swing. On the other hand, a shorter pendulum will have a faster swing due to its shorter distance.

3. How does the mass of a pendulum affect its motion under the influence of gravity?

The mass of a pendulum does not affect its motion under the influence of gravity. This is because the force of gravity acts on all objects equally, regardless of their mass. However, the weight of a pendulum, which is determined by its mass, can affect its swing as a heavier pendulum will have more inertia and thus require more force to move.

4. What is the relationship between the angle of release and the swing of a pendulum under the influence of gravity?

The angle of release, or the angle at which the pendulum is pulled back before being released, affects the amplitude (or height) of the pendulum's swing. The higher the angle of release, the greater the amplitude of the swing will be. This is because a higher angle of release gives the pendulum more potential energy, which is converted into kinetic energy as it swings.

5. How does air resistance affect the motion of a pendulum under the influence of gravity?

Air resistance can affect the motion of a pendulum, but its effect is usually minimal. In a vacuum, where there is no air resistance, a pendulum would continue swinging indefinitely. However, in the Earth's atmosphere, air resistance can cause the pendulum to lose some of its energy as it moves through the air. This can result in a slightly smaller amplitude and shorter swing time.

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