Tag Archives: Pendulum

Pendulums and Gravity

In the video above, I talk about how pendulums actually work. If you haven’t watched it, the principle is simple: an object is suspended from a fixed point and allowed to swing back and forth – the mass of the object and the time it takes to swing back and forth are independent of each other, relying only on the length of the string and the strength of gravity.

Normally, you’d think of gravity on Earth’s surface as being constant, but the Earth isn’t a perfect sphere, meaning that the force of gravity near the equator is slightly weaker than at higher or lower latitudes. And how did we discover this fact? Pendulums!

Pendulum and Gravity 1

In the year 1671, a French scientist named Jean Richer travelled to French Guiana. Among several experiments and astronomical observations during his two-year trip was to take measurements with a clock pendulum.

He set up the pendulum in the same way I did in my video, but he adjusted the length of the pendulum so that one half-swing took exactly one second, a common technique at the time. What he found was that the pendulum length needed to be slightly shorter than it did back in Paris, by about 3 millimeters. Though a small difference, it was significant enough to begin a discussion about the varying gravitational field of Earth.

Pendulum and Gravity 2

This was later proved by Isaac Newton by determining that due to the Earth’s rotation, it was thicker at the equator, meaning the surface was further away from Earth’s center of mass. This was further supported by Newton’s idea that gravitational force decreases as the distance between two objects increases.

Scientists started to use pendulums to take measurements of the gravitational field in other locations and began to create a model of the Earth’s true oblong shape. Since then, we’ve developed more accurate methods to measure the same thing, but they were pioneered by those first efforts.

Written By: Scott Yarbrough

Video Music: Funky Chunk Kevin MacLeod (incompetech.com)

Licensed under Creative Commons: By Attribution 3.0 License

http://creativecommons.org/licenses/by/3.0/

Pendulum Waves

You’ve already seen the way a no-flinch pendulum works, so now we are changing it up. This contraption is host to many pendulums next to each other but not touching. When you raise them up and let them go all at once, you can see something truly mesmerizing.

pendulum wave

They will all start to fall at the same rate, thanks to the laws of gravity, but after the first swing the will not be synchronized. This is due to them being uncoupled, or not connected, and to the length of each individual pendulum. The pendulum furthest away has the shortest length and the closest pendulum has the longest. All of the pendulums in the middle gradually become longer as they get closer.

The period of a pendulum is mostly dependent on its length. Since the lengths gradually increase, so will the periods, causing them to become out of sync. However, that can cause some pretty visually pleasing effects!

pendulum wave middle

Of course, given enough time, all of our pendulums will eventually line back up again in the end. But not before going through some other awesome patterns, as well as what may look like chaos.

pendulum wave end

This is not the easiest DIY project, but it is possible to recreate, so give it a try. Or you can always find it online or in store, but either way it is definitely worth seeing in person. Let us know what you think!

Written By: Mimi Garai

Ready, Set, No Flinch Pendulum! Thats Science!

The conservation of energy tells us that a bowling ball won’t swing higher than the initial height if there is no force added. But should we still believe that in a high risk situation? We are putting the laws of physics up to the test.

Caution: Do not try this at home without parental supervision.

Sir Isaac Newton says the total energy an object has will alway stay the same, unless you do something to change it (push or pull it). The system will start with a certain amount of potential energy, the energy possessed by a body by virtue of its position relative to others. When you raise the bowling ball to face level you are putting energy into the system in the form of work. Work is done when a force is applied to an object and the object is moved through a distance.

pendulum

When you let go of the bowling ball and it starts to swing the ball will gain kinetic (or moving) energy, and lose it’s potential energy proportionally. This proportional loss and gain ensures the total energy of the system remains constant.

At the bottom of the pendulum (when the bowling ball is closest to the floor), all of the potential energy has been converted to kinetic energy. Therefore, the amount of kinetic energy in the ball is equal to the total energy of the system.

Pendulum science

On the upswing of the pendulum, the kinetic energy will start to convert back into potential energy. This will happen until it reaches your face, where there is no longer kinetic energy, but instead the potential energy is equal to the total energy.

This pattern of gain and loss of potential and kinetic energy would continue on and on in perfect conditions. However, here on Earth, there is no such thing as perfect. With each swing of the pendulum there is a little bit of energy lost due to friction in the rope. This loss of energy will dampen each swing, causing the maximum height of swing to go down each time.

science pendulum

This is a great way to test yourself to see if you trust in the laws of physics. Would you have to guts to face up to the no flinch pendulum?

 

Written by: Mimi Garai

The Pendulum Challenge

Think you could stand still with a bowling ball swinging towards your nose? It’s tough! This scary experiment is governed by the same principle that decides the dynamics of a car crash and guides trick shots on a pool table: a gigantically important physical law called conservation of energy. This law states that if a system is left alone, its total energy doesn’t change.

Pendulum1

A system’s total energy is composed of two parts: kinetic energy (the system’s motion) and potential energy (stored energy determined by the system’s position). Let’s think about our bowling ball when it’s suspended at head height. It’s not moving, so its kinetic energy is zero. We know that if we stop holding it up, it will fall. This means it has potential energy! this case, the potential energy comes from Earth’s gravity pulling on the bowling ball.

When we release the bowling ball, it begins to move. In other words, its potential energy starts turning into kinetic energy. This happens bit by bit: when the bowling ball has fallen a few inches, it’s not going very fast yet, and it still has most of its original gravitational potential. As it falls farther, more of its gravitational energy is converted to kinetic energy, so the ball picks up speed. The tradeoff continues smoothly and proportionally until all potential energy has been converted to kinetic energy. The bowling ball moves fastest (has highest kinetic energy) when it’s closest to the ground (has lowest gravitational potential energy).

Diagram

Credit: BBC

 

No physical system is perfectly efficient. Air resistance and stretch in the tether damp the swinging bowling ball’s momentum. A tiny bit of energy is dissipated with each turn of the pendulum until, finally, it comes to rest. Since each pass of the bowling ball carries less energy than the one before, the pendulum swings a little lower every time. As long as you drop the weight cleanly from your nose, it’s perfectly safe to stay put.

Pendulum2

It’s one thing to know that the bowling ball can never swing back up to its original height and crash into your nose… it’s quite another to override your body’s instinct to flinch or step back!

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