In simple terms
A friendly intro before the formal notes — no formulas yet.
The Body's Physics Toolkit
Our bodies use fundamental physics principles like levers and forces to create every movement. Understanding these rules is like having a user manual for athletic performance, helping us to move more efficiently and powerfully.
Imagine your body is a complex construction site. Your bones are like cranes and crowbars (levers), your muscles provide the engine power (effort), and the weights you lift or the balls you throw are the loads (resistance). By understanding the physics of how these tools work, you can lift heavier loads and move things faster, all while staying safe. Biomechanics is simply learning the instruction manual for your body's toolkit.
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First, for any movement like a bicep curl, identify the lever system. Pinpoint the fulcrum (the joint, e.g., elbow), the effort (where the muscle attaches, e.g., bicep insertion), and the resistance (the weight being moved, e.g., a dumbbell).
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Next, apply Newton's Laws. To start the curl, the force from your bicep must overcome the dumbbell's inertia (Newton's 1st Law). The amount of force you apply determines how quickly the dumbbell accelerates (Newton's 2nd Law).
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Then, analyse the type of motion. If you throw the dumbbell, it becomes a projectile. Its path is determined by the speed, angle, and height of release. Optimising these factors maximises the distance it travels.
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Finally, consider any rotation. If an athlete is spinning, like an ice skater, they are demonstrating angular momentum. By pulling their arms in, they decrease their moment of inertia and, to conserve momentum, their speed of rotation increases.
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Full topic notes
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Levers in the Human Body
Our musculoskeletal system functions as a series of levers. Bones act as the rigid lever arms, joints serve as fulcrums (or pivots), and muscles provide the effort to move a resistance, which could be a part of the body, a piece of equipment, or gravity itself. There are three classes of levers, distinguished by the relative positions of the fulcrum, effort, and resistance.
Mechanical Advantage (MA) =
First-Class Levers (EFR/RFE): The fulcrum is between the effort and resistance. They can provide either a mechanical advantage or disadvantage. Example: the action of the triceps extending the elbow.
Second-Class Levers (FRE): The resistance is between the fulcrum and the effort. These levers always provide a mechanical advantage (MA > 1), meaning less effort is required to move a large resistance. They are uncommon in the human body. Example: plantar flexion at the ankle.
Third-Class Levers (FER): The effort is between the fulcrum and the resistance. These are the most common levers in the body. They always have a mechanical disadvantage (MA < 1) but provide a large range of motion and high velocity, which is essential for throwing and striking actions.
Newton's Laws of Motion in Sport
Sir Isaac Newton's three laws of motion are the bedrock of mechanics and are fundamental to understanding how athletes generate and control movement. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces.
First Law (Inertia): A rugby ball placed on the kicking tee will remain there until the kicker applies a force to it. Similarly, a moving ice hockey puck will continue to glide in a straight line until friction or a player's stick changes its state of motion.
Second Law (Acceleration, F=ma): To accelerate a shot put (high mass) to a high velocity requires a massive force from the athlete. The same force applied to a lighter tennis ball (low mass) would produce a much greater acceleration.
Third Law (Action-Reaction): When a swimmer pushes against the water with their hands and feet (action), the water pushes back on the swimmer with an equal and opposite force (reaction), propelling them forward. The same principle applies to a high jumper pushing off the ground.
Projectile Motion and Rotational Mechanics
Many sports involve projectiles—objects or bodies that are thrown, struck, or kicked into the air. The path of a projectile, its trajectory, is influenced by several key factors. Additionally, many sports involve rotation, which is governed by the principles of angular momentum. Understanding these concepts is vital for optimising performance in sports like diving, gymnastics, and discus.
Projectile Motion Factors: The trajectory of a projectile (e.g., a javelin) is determined by: 1) Speed of release (greater speed = greater distance), 2) Angle of release (the theoretical optimum is 45°, but varies depending on release height), and 3) Height of release (greater height increases flight time and distance). Air resistance also plays a significant role.
Angular Momentum: This is the 'quantity of rotation' a body has. It is calculated as Moment of Inertia × Angular Velocity. According to the principle of conservation of angular momentum, if no external torque acts on a body, its angular momentum remains constant. This is why an ice skater spins faster when they pull their arms in—they decrease their moment of inertia, so their angular velocity must increase to keep angular momentum constant.
Bernoulli's Principle: This principle explains how lift is generated. An object shaped like an aerofoil (e.g., a discus, ski) forces air to travel faster over its curved top surface than its flat bottom. This creates lower pressure on top and higher pressure below, resulting in a net upward 'lift' force that increases flight time and distance.
Worked examples
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During a bicep curl, the biceps muscle inserts 5 cm from the elbow joint (fulcrum). The athlete is holding a 100 N dumbbell at a distance of 35 cm from the elbow joint. Classify the lever and calculate its mechanical advantage.
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Identify Components & Classify: The fulcrum is the elbow joint. The effort from the bicep is applied between the fulcrum and the resistance (dumbbell). This arrangement is a third-class lever.
A sprinter with a mass of 75 kg accelerates from the starting blocks. The blocks exert an average horizontal force of 900 N on the sprinter. Calculate the initial acceleration of the sprinter.
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Identify Knowns: Force (F) = 900 N, Mass (m) = 75 kg.
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What are the three components of a lever system?
Fulcrum (pivot point), Effort (force applied), and Resistance (load to be moved).
Key takeaways
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First-Class Levers (EFR/RFE): The fulcrum is between the effort and resistance. They can provide either a mechanical advantage or disadvantage. Example: the action of the triceps extending the elbow.
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Second-Class Levers (FRE): The resistance is between the fulcrum and the effort. These levers always provide a mechanical advantage (MA > 1), meaning less effort is required to move a large resistance. They are uncommon in the human body. Example: plantar flexion at the ankle.
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Third-Class Levers (FER): The effort is between the fulcrum and the resistance. These are the most common levers in the body. They always have a mechanical disadvantage (MA < 1) but provide a large range of motion and high velocity, which is essential for throwing and striking actions.
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Test Your Knowledge on Movement Analysis
Test Your Knowledge on Movement Analysis
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