What keeps that water inside the bucket when you spin round and round at speed? Is it some miraculous force, or something completely different?
Read on to find out.
What is the centrifugal force?
We'll kick things off with a quick definition:
"Centrifugal force, a fictitious force, peculiar to a particle moving on a circular path, that has the same magnitude and dimensions as the force that keeps the particle on its circular path (the centripetal force) but points in the opposite direction."
Note the inclusion of the qualifier "fictitious". This means that while it is commonly referred to as a force, this is not the case. It is, in fact, an effect of something else going on -- centripetal force.
A common analogy to use to explain the apparent phenomena is to imagine a stone tied to a string. The string is, in turn, tied to a post in the ground and the stone (and string) are spinning around the post in a single horizontal plane.
The stone is continuously changing the direction of its velocity relative to the ground, and has, therefore, an acceleration towards the post.
Thanks to Newton's Second Law, we know that acceleration is caused by a force, which in this case would be the tension of the string. If we assume that the stone is moving at a constant speed and gravity is ignored for the purposes of our analogy, the inward-pointing string tension is the only force acting on the stone.
Now, imagine the string breaks. Where will the stone go?
That's right, it will travel in a straight line forward from the point that the string broke. This is because the stone, which has inherent inertia, will keep moving in a straight line tangent to its previous circular path.
Think of how a sling or catapult works if you want to conceptualize this (ignoring gravity's inevitable influence on the stone's trajectory, of course).
It will not move in an outward direction as it would if centrifugal force was a real thing. For this reason, this apparent force is more accurately termed the centripetal effect or force.
What is the difference between centrifugal and centripetal forces?
We have already covered what is meant by the centrifugal force, but what differences, if any, are there with the centripetal force?
Let's include another definition to help clear things up.
The centripetal effect is defined as "the force that is necessary to keep an object moving in a curved path and that is directed inward toward the center of rotation."
This fits very nicely with our previous analogy of a swirling stone attached to a pole stuck in the ground. The only real difference is the frame of reference for either of them.
According to Andrew A. Ganse, a research physicist at the University of Washington, "the difference between centripetal and centrifugal force has to do with different 'frames of reference,' that is, different viewpoints from which you measure something.
"Centripetal force and centrifugal force are really the exact same force, just in opposite directions because they're experienced from different frames of reference," he added.
In other words, if you were observing the rotating system from the outside, the would "see" an inward centripetal force acting to constrain the rotating body to a circular path. But, if you are actually part of the rotating system, you will experience an apparent outward "push" from the center of the circular path.
However, the "force" you would experience is actually the centripetal force that is keeping you from going off on a literal tangent.
Got it? Good.
How do you calculate centripetal force?
Centripetal force, as we have previously mentioned, is the force necessary to keep an object moving in a curved path and that is directed inward toward the center of rotation.
In other words, the force is always "seeking" the center. To this end, the centripetal force can be represented using the following formula:
F = m x v2/r
F = The magnitude of centripetal force
m = mass of the object
V2 = is the velocity of the object squared
r = is the radius of the curvature arc
Note that the centripetal force is, therefore, proportional to the square of the velocity of a moving object. This means that a doubling of the velocity will result in a quadrupling of the force required to move it.
The force can also be increased by either increasing the mass of the object being spun or reducing the radius of the spin.
What are some real-life applications of the centripetal force?
And so, without further ado, here are some real-life applications of the centripetal effect. This list is far from exhaustive and is in no particular order.
1. Training astronauts for being blasted into space
One application of centripetal force is astronaut space launch simulators. When a rocket first blasts off it is laden with fuel and oxidizer, and moves slowly.
As it ascends, it burns fuel at an eye-watering rate and is, therefore, continuously losing mass. This dramatically changes the interplay of the rocket's mass with its constant thrust.
This, therefore, causes the acceleration of the rocket to increase to several times that of normal gravity towards the end of its boost phase. NASA simulates this using enormous centrifuges that prepare astronauts for this extreme acceleration.
The force is simulated by the seat back pushing inward on the astronaut within the simulator.
2. Laboratory centrifuges rely heavily on the centripetal effect
One important application of the centripetal force is a laboratory centrifuge. A centrifuge is a machine that uses force to separate substances of different densities (solids with higher density will be deposited near the edge of the centrifuge container, while the lighter solids will be concentrated near the center of the container). This is possible thanks to the phenomenon of centripetal force.
Centrifuges are often used to separate the components of blood. Under normal gravity, thermal motion causes continuous mixing of blood components and blood cells from settling out of suspension from a blood sample.
However, when spun in a centrifuge, the force causes heavier components, like red blood cells, to settle at the bottom of the container, with the platelets above them, then the white blood cells and the plasma at the very top, according to their relative densities.
3. Some amusement park rides take advantage of centrifugal forces
Another application of centripetal force is in amusement park rides. Rides like the Gravitron, for example, pin riders to a wall using centripetal forces.
Not only that, but the ride will generally also incline while keeping riders pinned and elevated off the machine's floor in apparent defiance of Earth's gravity.
Fun, and educational!
4. Centrifugal governor's make excellent use of centripetal forces
These fascinating devices are used to regulate the speed of an engine by using spinning masses, that move radially, to adjust the engine's throttle as the engine changes speed. The governor is usually connected to a throttle valve that regulates the flow of working fluid (like steam) supplying an engines' primer mover.
As the speed of the prime mover increase, the central spindle of the governor will rotate faster, and the kinetic energy of balls will increase. The movement of the governors spinning balls, or arms, is dictated by the principles of centripetal force.
5. Spin casting or centrifugal casting also use it
And another application is in spin casting. Also known as centrifugal casting, this production method uses the principles of the centripetal force to disperse liquid metal or plastic evenly through the negative space of a mold.
The process involves the spinning of a mold and casting material is then introduced to the mold while it is in full spin. This production method greatly accelerates the production rates of certain cast materials and preserves the fine details, if any, for castings of metal, plastic, or wax.
And that's a wrap ladies and gentlemen.
These are but a few of the many examples of applications of centripetal force. Can you think of any others?