Introduction
Skateboarding has emerged as a popular recreational activity primarily common among young people. It involves various mechanisms that allow the rider to perform numerous tricks. The skateboard has three key parts: the deck, the trucks, and the wheels. This gravity-defying sport has evolved to feature a kicktail on the board’s back and front end.
The popularity of skateboarding has grown over the years, along with innovations in skateboard materials and designs, which have helped riders improve their skills and incorporate new tricks such as the ollie. Today, skateboarding encompasses a range of dynamics, from disciplines to styles. The physics behind these tricks and skateboarding in general is complex but interesting, from mechanics to energy conservation. Physics is applicable in daily activities, including balancing and riding a skateboard.
Mechanics of Skateboarding
The three primary parts of a skateboard are the wheels, the truck, and the deck. When assembling a personalized board, all these parts have to be present. Since skateboards can be designed in different ways, deck materials and sizes can vary. Common deck types include shortboards, longboards, cruisers, and old-school boards (Skateboards.com, 2023).
The deck serves as the base on which the riders place their feet and other parts of the skateboard, including the grip tape and bolts. While the deck connects everything, the truck is more complex as it contains the most components. Typically, the truck allows the board to turn, move, and maneuver around. The choice of deck type impacts the size of the trucks.
Axles, hangers, baseplates, bushings, and kingpins include the parts contained within the trucks (Skateboards.com, 2023). On the other hand, the wheel encompasses ball bearings and axle nuts. The synergy among these sections inspires the skater to reach new heights.
Newton’s laws of motion explain how people control the movement of skateboards. According to the first law, a skateboard only moves when a rider exerts force on it. First, a person will place one foot on the board and use the other to push it off the ground, generating force that moves the skateboard forward.
According to the Glenn Research Center (2023), the second law states that acceleration and force are positively correlated. For instance, a skateboard with greater mass accelerates more slowly than one with less mass. When a rider wants to go faster, they push the board harder off the surface, creating a greater force that acts on the skateboard. An increase in force has a similar impact on acceleration. Newton’s third law of motion posits that every action reacts, either equal or opposite; action and reaction forces create motion (Glenn Research Center, 2023). When a skater pushes the board harder against the ground, it will move faster and farther.
Friction and Skateboarding
Among the forces that affect motion is friction, which acts on skateboards and skaters. Friction causes the wheels to move in opposite directions to their motion. When the force applied by the rider exceeds friction, the board moves forward and slows when the skater stops pushing. This occurrence supports the assumption that friction opposes motion, as demonstrated by Laroche et al. (2023).
However, the materials of the skateboard and the surface determine the amount of friction. Compared to smoother surfaces, rougher areas create more friction. Skaters can stand on their boards without slipping or falling due to friction. Some riders cover the deck with grip tape, which has a rough surface, to increase the resulting friction between the deck and their shoes. In turn, this reduces sliding and makes it easier for people to stay on the deck while skateboarding.
Heavier objects pressed against a surface with immense force are more likely to create greater friction. Three types of friction are involved in skateboarding: rolling, static, and sliding. Static friction happens between the board and the rider’s shoes, while sliding friction occurs when the skateboard slides over a surface.
Rolling friction is weaker than static and sliding friction and acts when the wheels roll over the ground. Some wheels, such as ceramic wheels, are designed to reduce friction because they are harder and smoother. Without external action, the skateboard stops due to the rolling friction between the surface and the wheels. Riders often stop the board by stepping on its back to scrape the ground, creating friction that works against the skateboard’s motion and eventually slowing it to a stop. Friction in skateboarding can be reduced by choosing the right surface, using harder or larger wheels, or applying wax to the board.
Momentum
In some cases, objects in motion are easier to stop than others, and this difference is related to momentum. Every object has mass, which implies that it has momentum when it moves. As articulated by Jalilvand et al. (2019), an object’s momentum depends on its velocity and mass. Therefore, momentum is the product of an object’s mass and velocity; it is a direct relationship. An increase in velocity or mass would result in an escalated momentum.
Skateboards gain more momentum when moving faster than when in slow motion. For this reason, if two skaters roll down the road at the same velocity, the board with greater mass will have more momentum. Furthermore, skaters normally use angular momentum conservation for high-pipe jumps. As they jump into the air, the skater and the board rise, remaining glued together.
When considering the half-pipe as a quarter of a circle, the skater is rotating in a circular motion as they move along it, and it is a U-shaped ramp used for boarding. This occurs at the axis of rotation, which is a distance far from the half-pipe. At the same time, the momentum of inertia increases with distance from the rotation axis.
When the rider crouches as they approach the half-pipe, their center of mass moves farther from the rotation axis, thereby increasing their moment of inertia. As they go over the half-pipe, the skater extends their body straight and waves their hands in the air, moving the center of mass upwards and closer to the rotation axis. Subsequently, the angular velocity increases, giving the rider more speed as they hit the top and fly into the air, allowing them to perform various tricks. This demonstrates how people apply the principle of momentum during skating.
Energy Conservation
A skater’s efficiency can be affected by energy conservation. In particular, the law of conservation applies to skaters as their energy is converted between various forms. For instance, potential energy gets converted into kinetic energy as the rider drops onto a surface.
Next, kinetic energy is transferred to the boars as the skater performs their desired tricks. Apart from angular momentum, people who skate on half-pipes also leverage the conservation of energy. Energy can be broken into two types: potential and kinetic (Manzhos et al., 2022).
Potential energy depends on the force the skater feels, but in skateboarding, it is gravity. When it comes to gravity, the potential energy tends to be proportional to the level of the boards above the ground. If the skater is high above the surface, they have more potential energy.
Kinetic energy is proportional to the square of an object’s velocity and is associated with an object’s movement. Manzhos et al. (2022) confirmed that the total amount of potential and kinetic energy is always constant but can be transferred. For a skateboarder, they normally start from a high point or at the top of a half-pipe, giving them significant potential energy.
However, there is no kinetic energy at this point since the skateboarder is starting at rest. This implies that the skater’s total energy equals their potential energy. As the rider jumps down on their skateboard and rolls down the half-pipe, they lose potential energy as speed increases, indicating the conversion of potential energy to kinetic energy. Once at the bottom of the half-pipe, all potential energy is lost, while kinetic energy remains high as speed, which the skater can use to launch into the air and reach the other side of the ramp.
Center of Mass and Balance
The skateboard’s center of mass (CoM) is in the middle of the board. In essence, the CoM is usually pulled down by gravity (Fardaei, 2023). When the nose of the board rises, the center of mass begins to increase. Skateboarders must keep their CoM over the base of the board to maintain balance, or they will fall flat on the surface.
People who skateboard normally experience minimal difficulty with keeping their feet close to the board during normal movement, but jumps require more thought. In circular motions, the board’s CoM is at a point that remains motionless while the wheels undergo circular motion. If the skater fails to balance their CoM, they will be off-center spin.
Moreover, the center of gravity is the point where the skater’s and the skateboard’s weight is evenly distributed. When working on their balance, the skateboarder must distribute their weight accordingly on the board. The first step is to determine the preferred stance for balancing on the board.
Next, the skater places their feet behind the bolts, since being in the middle of the board gives them less control. Keeping the body weight centered and shifting it slightly helps the skater to remain stable. When the rider carefully stands and balances on the skateboard deck, they do not move across the surface, and an applied force in a specific direction is key to getting started.
Conclusion
Understanding the physics of skateboarding reveals the sport’s simplicity. Skateboards are primarily made up of the deck, trucks, and wheels, which are connected by other components such as bolts, axles, grip tape, and ball bearings. Newton’s law of motion explains how a skateboarder gets to move the board forward from a point of rest.
The forces involved in skateboarding include friction, applied force, and gravity. Momentum and energy conservation equally play a role in the tricks performed by a skateboarder. While skateboarding appears to be a simple sport on the surface, several factors allow the rider to increase and decrease their speed and reach certain heights as they skate.
References
Fardaei, J. (2023). The mythos of gravity. London Journal of Research in Science: Natural and Formal, 23(13), 35-50.
Glenn Research Center. (2023). Newton’s laws of motion. Glenn Research Center | NASA.
Jalilvand, F., Banoocy, N. K., Rumpf, M. C., & Lockie, R. G. (2019). Relationship between body mass, peak power, and power-to-body mass ratio on sprint velocity and momentum in high-school football players. The Journal of Strength & Conditioning Research, 33(7), 1871-1877.
Laroche, A., Naga, A., Hinduja, C., Sharifi, A.A., Saal, A., Kim, H., Gao, N., Wooh, S., Butt, H.J., Berger, R., & Vollmer, D. (2023). Tuning static drop friction. Droplet, 2(1).
Manzhos, S., Sasaki, E., & Ihara, M. (2022). Easy representation of multivariate functions with low-dimensional terms via Gaussian process regression kernel design: applications to machine learning of potential energy surfaces and kinetic energy densities from sparse data. Machine Learning: Science and Technology, 3(1).
Skateboards.com. (2023). From grip-tape to bearings: Understanding the basics of skateboard components.