B1.4 Levers and Movement

🔩 What Is a Lever?

✔ A rigid rod that rotates about a fulcrum (pivot)

✔ A lever is a simple machine

🔄 Rotation Depends On

📏 Magnitude of force applied

↔ Distance from fulcrum to line of action of the force

🦴 Levers in the Human Body

✔ Bones act as levers

💪 Muscle contraction provides the force

🔄 Creates a tendency for rotation at joints

🎯 Focus of This Chapter

✔ Differences between the three types of levers

✔ Use of mechanical advantage to assess lever efficiency

Parts of a lever:

🦴 A fulcrum is made up of:

✔ Rigid rod

🔘 Fulcrum (axis)

📦 Load force

💪 Effort force

📏 Lever Arms

↔ Moment arm → perpendicular distance from force to fulcrum

📦 Load arm → distance from load to fulcrum

💪 Effort arm → distance from effort to fulcrum

Torque:

⚡ Force – a push or pull that causes an object to start or stop moving. This is often in a linear path ↔

🔄 Torque – rotational force, or a tendency to cause rotation about a fixed point ⭕

📏✖⚡ Torque calculation – torque is calculated by multiplying a force by the distance from the fulcrum at which the force is applied

🧮 Torque formula
Torque (τ) = Force (F) × Distance from fulcrum (moment arm)

📐 Example calculation
If:

⚡ Force = 50 N

📏 Distance from fulcrum = 0.4 m

➡ Torque = 50 N × 0.4 m = 20 Nm

Mechanical advantage of a lever:

🔧 If you were manipulating a lever…

📏 The length from fulcrum to you is called the effort arm.

📦📏 The length from the fulcrum to the object you are lifting is called the load arm.

💪🔄 If the effort arm is very large, it will cause a very high torque.

⚖⬆ This means you would be able to lift a very heavy object with relative ease.

💪Mechanical advantage describes how much the effort force is multiplied to overcome a load

📈It indicates the efficiency of a lever in moving a resistance

It is a measure of how much your effort is multiplied

A mechanical advantage of 10 means if you apply 5N of force, it will lift a 50N object

A mechanical advantage of 0.4 means that if you apply 10N of force, it will lift a 4N object.

This can be calculated either two ways

𝑀𝐴=  (𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑒𝑓𝑓𝑜𝑟𝑡 𝑎𝑟𝑚)/(𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑙𝑜𝑎𝑑 𝑎𝑟𝑚)=  (𝑀𝑎𝑔𝑛𝑖𝑡𝑖𝑢𝑑𝑒 𝑜𝑓 𝑙𝑜𝑎𝑑)/(𝑀𝑎𝑔𝑛𝑖𝑡𝑢𝑑𝑒 𝑜𝑓 𝑒𝑓𝑓𝑜𝑟𝑡)

Any MA greater than 1.0 is regarded as very effcient.

Lever types:

✔ Three types based on positions of effort, load, and fulcrum

🔁 First-Class Lever

⚖ Effort and load on opposite sides of fulcrum

↔ Effort arm can be smaller, equal to, or greater than load arm

❗ Fairly rare in the human body

🏋 Second-Class Lever

📍 Effort and load on the same side of fulcrum

📏 Effort arm longer than load arm

✔ MA > 1 → small effort overcomes large resistance

❗ Very rare in the human body

🚀 Third-Class Lever

📍 Effort and load on the same side of fulcrum

📏 Effort arm shorter than load arm

❌ MA < 1

✔ Advantage = greater range of motion and speed

🔁 Very common in the human body

Levers in body:

🔁 First-Class Lever

⚖ Effort and load on opposite sides of fulcrum

↔ Effort arm can be smaller, equal to, or greater than load arm

❗ Fairly rare in the human body

 All muscles in the body act as levers…

First class – the skull balances on the spine (fulcrum), the weight of the head (load) is mostly anterior, muscles in the back of the head/neck (effort) keep the head balanced.

🏋 Second-Class Lever

📍 Effort and load on the same side of fulcrum

📏 Effort arm longer than load arm

✔ MA > 1 → small effort overcomes large resistance

❗ Very rare in the human body

All muscles in the body act as levers…

Second class – body weight (load) rests on the center of the foot, the calf muscles (effort) pull via the achilles tendon at the heel, and pivot at the toes (fulcrum)

🚀 Third-Class Lever

📍 Effort and load on the same side of fulcrum

📏 Effort arm shorter than load arm

❌ MA < 1

✔ Advantage = greater range of motion and speed

🔁 Very common in the human body

All muscles in the body act as levers…

Third class – Weights (load) held in the hand are lifted by the bicep muscles (effort) that insert on the proximal end of the radius, and pivot at the elbow (fulcrum)

🔁 First-Class Lever

✔ MA can be greater than or less than 1.0

🏋 Second-Class Lever

✔ MA > 1.0

📏 Effort arm always longer than load arm

🚀 Third-Class Lever

❌ MA < 1.0

📏 Effort arm always shorter than load arm

🧱 Key Parts of a Lever

💪 Effort → force applied to lift the object

🔘 Fulcrum → pivot point

📦 Load → object being lifted

📍 Fulcrum Position Matters

✔ Fulcrum closer to the load

⚖ Mechanical advantage

↓ Less effort needed to lift the load

❌ Fulcrum closer to the effort

⚠ Mechanical disadvantage

↑ More effort needed to lift the load

🎯 Key Idea

✔ The position of the fulcrum relative to effort and load determines whether lifting is easier or harder

⚙Third-class levers Very common in the human body 🦴

📉Have a low mechanical advantage (MA < 1) Muscles must produce large forces even to lift relatively light loads 💪

Key benefit: muscles insert close to the joint, allowing

🔄Large range of motion

⚡High movement speed

📏Muscles change less in length, while the limb moves through a much larger distance

🚫If a muscle (e.g. biceps) inserted farther from the joint, joint movement would be greatly limited

🦴 Arm acts as a lever when throwing

💪 Effort: muscles provide the force to move the arm and throw the ball

🔄 Fulcrum: the shoulder joint

⚾ Load: the ball being thrown

🚀 Longer lever (arm) allows greater distance and speed of projection (assuming technique is equal)

Levers outside the body in sports:

💪 Effort → force applied by the performer to move the lever

🔘 Fulcrum → turning point of the lever (shoulder joint when swinging a bat)

📦 Load → object being hit or moved (the baseball)

📍 Effect of Lever Position

✔ Fulcrum closer to the load

Increases power and speed

❌ Fulcrum closer to the effort

Increases control and accuracy

🎯 Key Idea

✔ Adjusting effort, fulcrum and load positions can enhance power, speed, control and accuracy in sport