Why doesn't a pendulum stop once it reaches equilibrium position?

Question

why (in terms of forces)?

Answer 1

This is most easily explained first in terms of energies.

An object has 'Kinetic energy' when it is in motion.
KE=(1/2)mv^2 ie. the kinetic energy equals one half of the mass times the velocity squared)

When you hold a pendulum above its equilibrium point, it has 'Potential Energy' meaning that if you let go, it will be pulled downward by the Earth's gravitational field and will gain Kinetic Energy.
PE=mgh ie. potential energy equals the mass of the object, times the gravitational constant (-9.81m/s^2 at Earth's surface) times its height (in metres) above its minimum height (it's equilibrium point in this case).

Energy is always conserved, ie PE+KE is constant for any system, so when potential energy is lost, kinetic energy is gained, and vice versa.

So at the top of the swing, the pendulum has its maximum potental energy, and no kinetic energy. But at the bottom of it's swing all it's potential energy is gone, turned into kinetic energy. And object with lots of kinetic energy will keep moving until it loses it! As is goes up the other side of the swing, it loses the kinetic energy, and regains its potential energy. Then the same thing happens all over again!

We can also say that when an object is in motion (ie has kinetic energy) it also has a certain momentum (p), given by p=mv. ie. momentum equals the mass times the velocity. The momentum will cause it to keep moving even while gravity opposes its motion. As it goes up, it loses momentum. Eventually gravity wins at the top of the swing, and the pendulum starts coming back down, gaining momentum as it moves. At the bottom of the swing momentum has a greater force than gravity again, so it moves through the equilibrium and goes up the other side. Repeat!

Answer 2

'Equilibrium' means that all of the forces acting on an object sum to zero. But at the vertical position, there is a force (called 'momentum') acting on the pendulum. You should get a physics book and read up on it ☺


Doug

Answer 3

Eventually, it does. Until then, the momentum will continue to swing past the equilibrium point until it runs out of steam - air and pivot friction and gravity.

Answer 4

that's basically nit choosing yet i might say it nonetheless has kinetic skill at equilibrium and might desire to circulate that into something else to be at relax. It basically transfers it into the skill skill of the spring and then the spring transfers it into the kinetic skill of the item....

Answer 5

it is acted upon by restoring force,
inertia of motin and the kinetic energy it posseses