Explore The Science Of Wheelies: How Physics Makes This Motorcycle Manoeuvre Possible

Have you ever seen a motorcycle rider pop a wheelie and wondered how on earth they do it without toppling over? In this article, we'll understand the physics behind wheelies while exploring concepts such as torque, angular momentum, and how they all come together to create that gravity-defying moment.

Wheelie And Its Physics

In the context of motorcycles or bicycles, a wheelie is a manoeuvre where the front wheel is lifted off the ground while the back wheel remains in contact with the ground. This can be achieved by accelerating at top speed while shifting weight towards the back of the bike, which causes the front wheel to rise. Wheelies are often used for stunts and are a popular technique in motorcycling and BMX biking. However, they can also occur unintentionally and may pose a safety risk if not executed properly.

To explore the physics behind the wheelie manoeuvre, it's essential to understand the multiple forces and factors involved.

Angular Momentum And Torque

Angular momentum is a fundamental concept in physics, which can be defined as the measure of the momentum of a body that is in rotational motion, moving in circles. In simpler terms, it can be thought of as the "spin" or "twist" that a rotating object possesses. More technically, the magnitude of an object's angular momentum is equal to the product of its moment of inertia (a measure of its resistance to rotational motion) and its angular velocity (the rate at which it is rotating around an axis). While the term "physics geeks" might imply that the concept is difficult to understand, anyone with an interest in physics can appreciate the importance and relevance of angular momentum.

In mathematics, angular momentum can be represented as,

$\mathrm{L}=\mathrm{I}\times \omega$

where L represents the angular momentum, I represents the moment of inertia and ω represents the angular velocity.

Angular momentum can be observed in a range of real-world examples, including a quarterback throwing a spinning ball or a bullet rotating as it leaves a gun. Everyday objects such as spinning tops, fans, and cars with turning wheels also demonstrate this concept. Angular momentum is fundamental in understanding natural phenomena and the principle of conservation of angular momentum is a key concept in physics.

Torque is a measure of the force that causes an object to rotate or twist. It is a concept that is commonly observed in everyday life, such as when you turn a doorknob, unlock a lock, or start a car by turning the ignition key. In technical terms, torque can be defined as the cross product of the force vector 'F', distance vector 'r', and the sine of the angle between the two vectors.

Now that you have understood angular momentum and torque, let's look at how these physical forces are involved in raising the front wheels of a motorcycle and performing a wheelie.

When a motorcycle travels on a flat surface, the force of gravity acts on the centre of mass of the motorcycle, while the ground exerts normal forces on the front and rear wheels in the opposite direction. This creates a balance of forces that allows the motorcycle to move smoothly.

To lift the front wheels of a motorcycle off the ground, the equilibrium between the opposing forces needs to be disrupted. This can be achieved by unbalancing the torques acting on the rear wheel.

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To execute a wheelie, the equilibrium between the opposing forces of gravity and normal forces must be disrupted. This is accomplished by accelerating the motorcycle, reducing the load on the front axle to zero, and increasing the torque applied to the rear wheel. The normal force on the rear wheel does not generate any torque, leaving gravity and the motorcycle engine to supply the necessary torque to the rear wheel through the drivetrain, resulting in a successful wheelie.

The Power And Optimal Conditions For Performing A Wheelie

The formula for calculating the power required to perform a wheelie is
P= mva

Where P represents power, m is the mass of the motorcycle, v is the velocity of the motorcycle, and a is the acceleration of the motorcycle.

This formula shows that the power required to perform a wheelie is directly proportional to the mass and velocity of the motorcycle. In practice, this means that it's easier to lift the front wheel with less power when the motorcycle is lighter and moving at a slower speed (without considering the power required to overcome air resistance as the motorcycle moves).

Performing a wheelie is easiest when the motorcycle is just starting to move, making it the optimal time to attempt a wheelie. In fact, it's so effortless at low speeds that riders often accidentally lift the front wheel without intending to do so. However, wheelies can be dangerous and should only be attempted by experienced riders in a safe and controlled environment.

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