What Is An Example Of Kinetic Energy In The Human Body?

Kinetic energy is the energy associated with motion. It refers to the work needed to accelerate an object of a given mass from rest to its current velocity. In the context of the human body, kinetic energy is generated when different parts of the body are in motion, such as when walking, running, or performing any other movement.

This article will provide an overview of kinetic energy in the human body and give examples of how it is utilized in different bodily functions and movements. The main forms of kinetic energy in the human body that will be covered are muscle contraction, walking/running, jumping, throwing/hitting, blinking, breathing, blood flow, and digestion.

Muscle Contraction

Muscle contraction involves the conversion of chemical energy from ATP into kinetic energy of motion. During muscle contraction, the myosin heads of the thick filaments attach to the actin filaments and pull them so that the bands of the myofibril slide over one another, resulting in contraction of the sarcomere and overall shortening of the muscle fiber (Ross, 2021). This process requires ATP hydrolysis, whereby the breakdown of ATP provides the energy needed for myosin to bind to actin and change its conformation to generate force and movement.

Specifically, ATP binds to the myosin head and is hydrolyzed to ADP and inorganic phosphate, releasing energy. This provides the power stroke that changes the angle of the myosin head, pulling the attached actin filament. Myosin then releases ADP and phosphate, allowing a new ATP molecule to bind and start the cycle again. So through numerous cycles of ATP binding, hydrolysis, and product release, the continual action of cross-bridge formation and power strokes converts chemical energy from ATP into mechanical energy and motion (Ross, 2021).

Overall, this chemo-mechanical process of actin and myosin sliding over one another, fueled by ATP hydrolysis, is how muscles transform chemical potential energy into kinetic energy and movement with each contraction.

Walking and Running

Walking and running are two common forms of human locomotion that rely heavily on kinetic energy. During walking, the body converts potential energy into kinetic energy with each step. As one leg swings forward, potential energy is built up as the center of mass rises. This potential energy is then converted into kinetic energy as the leg moves forward and the foot pushes off the ground (source). The kinetic energy allows the body to move forward. This pendulum-like exchange between potential and kinetic energy is repeated with each step.

Running also utilizes the conversion between potential and kinetic energy, but in a slightly different way. When running, there are moments where both feet are off the ground simultaneously. This means the body’s center of mass reaches a higher point than during walking, building up more potential energy. As each foot strikes the ground, this potential energy is again converted into kinetic energy to propel the body forward (source). The greater potential energy from the higher center of mass allows for more kinetic energy to be generated, resulting in faster forward motion.

Jumping

Jumping involves converting stored elastic potential energy in the muscles into kinetic energy (source). When the legs bend before jumping, the Achilles tendon and the arch of the foot stretch like an elastic band, storing elastic potential energy. The calf muscles also contract to store energy. As the legs straighten in the jump, this stored elastic potential energy gets converted into kinetic energy, providing power for the jump. The more the legs bend before takeoff, the more elastic potential energy gets stored, allowing for a greater jump height. At the peak of the jump, the person has maximum kinetic energy. When landing, the kinetic energy gets converted back into elastic potential energy as the muscles and tendons compress to absorb the impact.

Throwing and Hitting

Throwing and hitting objects involve rotation of body parts, which results in rotational kinetic energy. When throwing a ball, the rotation of the arm and torso generates angular velocity. The moment of inertia, which depends on the distribution of mass around the axis of rotation, determines the rotational kinetic energy together with the angular velocity. For a given angular velocity, more rotational kinetic energy can be generated by increasing the moment of inertia, such as by bringing the throwing arm farther back before releasing the ball.

The rotational kinetic energy is transferred to the ball when releasing it, adding to its translational kinetic energy. The amount of rotational kinetic energy depends on the moment of inertia of the rotating limb and the square of its angular velocity, according to the equation: rotational kinetic energy = (1/2) x moment of inertia x (angular velocity)^2 ^[1]. Faster rotation of the arm and keeping the arm extended farther from the rotation axis increases the rotational energy.

For hitting objects like baseballs, the batter rotates their arms and hips to build up rotational kinetic energy. More muscle torque applied over a longer rotation distance generates greater angular velocity and rotational kinetic energy, which gets transferred to the ball on impact. Proper timing of the hip and arm rotations is key to optimizing the kinetic energy transfer. The faster the bat speed on impact through this kinetic linking, the farther the ball will travel.

Blinking

Blinking involves the conversion of potential energy into kinetic energy. The eyelids contain elastic muscles that can stretch and store potential energy. When these muscles contract, that potential energy converts into kinetic energy that allows the eyelids to close rapidly.

Specifically, the orbicularis oculi muscle initiates blinking. This muscle surrounds the eye and contracts to close the eyelids. Right before a blink, the orbicularis oculi is stretched, storing potential energy like a coiled spring. When the muscle receives a signal from the brain to blink, it quickly contracts. The potential energy from the stretched muscle converts into kinetic energy that squeezes the eyelids shut.

The speed of an average blink takes around 100-150 milliseconds. The orbicularis oculi needs significant kinetic energy to close the eyelids that quickly. While a single blink may seem insignificant, the energy cost of blinking adds up. People blink around 15-20 times per minute on average, equating to over 10,000 blinks per day. Converting potential to kinetic energy allows our eyes to repeatedly and rapidly blink throughout the day.

Sources:

https://energykinetics.com/wp-content/uploads/2015/11/E-5-6_Tech_Dig_Mgr_Lights.pdf

https://www.littleinventors.org/ideas/blinking-energy-2000/details

Breathing

When we breathe, the diaphragm and intercostal muscles contract and relax to move air in and out of the lungs (Allison, 2018). This muscle movement requires kinetic energy. When the diaphragm contracts and moves downward, it decreases pressure in the chest cavity and allows air to rush into the lungs. This is an example of kinetic energy, as the diaphragm is converting potential energy from chemical reactions into kinetic energy of motion (Choi, 2018; “Kinetic Breathing,” n.d.). The rushing air into the lungs also contains kinetic energy. When we exhale, the diaphragm and intercostal muscles relax, increasing pressure and forcing air out of the lungs. Again, the muscles are converting chemical energy into kinetic energy to power their contraction and relaxation. So the process of breathing, involving the contraction and relaxation of respiratory muscles as well as the movement of air, utilizes kinetic energy.

Blood Flow

The heart generates kinetic energy to pump blood throughout the circulatory system. With each heartbeat, the heart contracts and pushes blood into the arteries, imparting kinetic energy onto the blood and propelling it forward [1]. The velocity and volume of blood being ejected from the heart determines the kinetic energy generated. During exercise, cardiac output increases to meet the demands of the working muscles. This requires the heart to pump more forcefully, generating greater kinetic energy in order to increase blood flow [2]. Patients with heart failure often have reduced kinetic energy of blood flow due to impaired heart function and contractility.

Digestion

The digestive system utilizes kinetic energy in the form of smooth muscle contractions to break down food and move it through the digestive tract (1). The stomach contains smooth muscle that contracts in a wave-like motion called peristalsis. These contractions churn and mix food, breaking it into smaller particles while also moving it onward toward the small intestine (2).

In the small intestine, peristalsis continues to push and squeeze food along the digestive tract, while mixing it with digestive juices. This back and forth motion ensures thorough contact between food particles and digestive enzymes. The kinetic energy exerted by these contractions facilitates the breakdown and absorption of nutrients (3).

Further along, the large intestine absorbs water from indigestible material and compacts feces via segmentation contractions. These rhythmic constrictions of the intestinal wall mix the contents and push them toward the rectum. Defecation, the elimination of waste, also requires coordinated muscle contractions of the rectum and anus (1).

Overall, the mechanical motion generated by smooth muscles is essential to moving food through each stage of chemical digestion and absorption. Without this kinetic energy, the digestive system could not efficiently extract nutrients and energy from food.

Conclusion

In summary, kinetic energy powers many essential bodily functions and movements. The contraction of muscles, from the large muscles used for walking and running to the small muscles that control blinking and breathing, rely on kinetic energy. Jumping, throwing, and hitting objects also require the conversion of chemical energy from food into kinetic energy of motion. Even automatic processes like blood circulation, digestion, and breathing involve kinetic energy being transferred in the form of cellular movements.

Kinetic energy allows us to move, breathe, pump blood, and perform countless actions that are vital to life. It is an indispensable form of energy that is constantly at work within the human body. By better understanding examples of kinetic energy, we gain insight into the invisible forces that drive our bodies. Appreciating this amazing source of energy can help motivate efforts to keep our bodies active and make the most of our innate kinetic abilities.