Centrifugal force

In Newtonian mechanics, a centrifugal force is a kind of fictitious force that seems to push objects outward when we look at things from a rotating frame of reference. This force appears to act perpendicular to the axis of rotation. It helps us understand how things behave in spinning systems.

The idea of centrifugal force makes it easier to study machines and natural movements that spin, like centrifuges, centrifugal pumps, and even planetary orbits. By thinking in terms of this force, scientists and engineers can simplify their calculations.

Actually, this outward push we feel isn’t a real force in the traditional sense. It can also be explained by looking at things from a steady, non-spinning view, where the behavior is just a result of objects wanting to move in straight lines due to their inertia.

History

Main article: History of centrifugal and centripetal forces

The idea of centrifugal force began in 1659 when Christiaan Huygens used the term in his notes. The word comes from Latin, where centrum means "center" and fugus means "fleeing." So, centrifugal force means a force that seems to push things away from the center.

In 1673, Huygens talked about clocks that move in circles and mentioned centrifugal force. That same year, Isaac Newton received Huygens's work and was excited to learn more about this idea. In 1687, Newton wrote more about centrifugal force in his famous book. Later, in the 1700s, people began to understand centrifugal force as a special kind of force that appears when things spin around. It has also been important in discussions about how we know if something is really spinning.

Introduction

Centrifugal force is an outward force that seems to act on objects when we look at things from a spinning viewpoint. This force isn’t real if we look from a steady, non-spinning viewpoint.

We always need a point of view to measure where things are and how they move. For instance, we could study how something moves inside an airplane by looking from the airplane, from Earth, or even from the Sun. A steady viewpoint, without spinning or changing speed, is called an inertial frame. We can study anything from this steady view without any centrifugal force. But sometimes, it’s easier to describe spinning things by using a spinning viewpoint — this makes the math simpler and the ideas easier to understand. When we choose this way, we notice fake forces, including the centrifugal force.

When we look from a spinning viewpoint, every object seems to feel a force pushing it away from the center of spinning. This force depends on the object’s mass, how far it is from the center, and how fast the viewpoint is spinning. People often feel this force when they’re on a merry-go-round or in a moving vehicle, which makes centrifugal force more familiar than the force that pulls toward the center, called centripetal force.

When we look from a spinning viewpoint, we also notice another fake force called the Coriolis force. If the speed of spinning changes, we need a third fake force, called the Euler force. These fake forces help us use Newton’s rules in a spinning viewpoint. However, these forces don’t follow Newton’s third rule — they don’t have matching forces pushing back in the same viewpoint. That’s why centrifugal force and the center-pulling force aren’t just action and reaction, as some people might think.

Examples

Vehicle driving round a curve

When you ride in a car that turns, you might feel like you are being pushed to the side. This feeling happens because of something called centrifugal force. If the car turns left, you feel pulled to the right. This is not a real force but seems real to you because you are moving with the car. The seat pushes you left to keep you from moving right, and this is what keeps you stable inside the car. To an observer watching from outside, your movement is just part of the car's turn.

Stone on a string

Imagine whirling a stone tied to a string in a circle. The string pulls the stone toward the center, keeping it in a circular path. If the string breaks, the stone flies off in a straight line. In a view that spins with the stone, we need to imagine an extra force — the centrifugal force — to explain why the stone doesn’t move toward the center even though the string is pulling it.

Earth

The Earth spins as it goes around the Sun, and this spinning creates a small centrifugal force. This force is usually tiny and does not affect our daily lives, but it does change how much we weigh. You would weigh slightly less at the equator than at the poles because of this force, along with the Earth being a bit bulged at the equator.

Weight of an object at the poles and on the equator

If you weigh something at the North Pole and then at the equator, it will weigh a little less at the equator. This is because the Earth's spin creates a small outward force at the equator, and also because the Earth is slightly wider there, bringing you farther from its center. Both effects make the gravity a bit weaker at the equator.

Main article: Newton's second law of motion

Main articles: Newton's first law of motion, centripetal force

Formulation

Main article: Rotating reference frame

See also: Fictitious force

When we look at things from a spinning viewpoint, like being on a merry-go-round, we notice something interesting. It seems like there’s an extra push that makes things fly outward. This is called the centrifugal force. It’s not a real push from something outside, but it appears because we’re looking at things from a spinning spot.

Imagine you’re holding a ball on a string and you spin around. The ball seems to want to fly outward, away from the center. This apparent push is the centrifugal force. It gets stronger if you spin faster or if the ball is farther from the center. The strength of this force depends on how heavy the object is, how fast you’re spinning, and how far the object is from the center you’re spinning around.

Absolute rotation

Main article: Absolute rotation

Sir Isaac Newton suggested three ways to tell if something is really spinning. One way is to watch water in a bucket. When the bucket spins, the water forms a special curved shape because it feels a pushing force away from the spin.

Another way is to tie two balls together with a string and spin them. The string gets tighter because of the same pushing force. These effects only happen when we are spinning, not when we are still. This helps us know if we are really spinning or just feeling like we are. For example, Earth is a bit squashed at the poles and wider around the middle because of this spinning force.

Applications

Many everyday machines and inventions work better when we think about a special kind of force called centrifugal force. This force seems to push things away from the center when they are spinning.

For example:

• A centrifugal governor helps control the speed of engines by using spinning weights that move out and in.
• A centrifugal clutch lets small engines start up without moving the machine until they spin fast enough.
• Scientists have ideas for space stations that spin to create a feeling of gravity, like on Mars.
• Factories use spinning to shape liquid metal or plastic into objects.
• Centrifuges spin to separate different materials, like separating cream from milk.
• Some fun rides spin so fast that you feel pushed against the wall and lifted off the floor!

Even though we can think about these things using centrifugal force, we can also understand them by looking at how things move without spinning.

Other uses of the term

The term centrifugal force is mostly used in science to describe a special kind of force that seems to push objects outward when looking from a spinning viewpoint. But sometimes, people use this term for other ideas too.

In a method called Lagrangian mechanics, scientists describe motion using different kinds of measurements. In this method, forces related to how fast something changes its position can sometimes be called centrifugal forces. These are similar to the usual centrifugal force in some cases but can mean other things too.

Another use of the term is for a force that pushes back against the force that keeps an object moving in a curve, like a circle. When something moves in a curve, it is being pulled toward the center by a force. Because of this, the moving object also pushes back with an equal force in the opposite direction. This backward push is sometimes called a centrifugal force, but it is really just the reaction to the force that keeps the object curving.