chapter2

Gravity: A force that pulls objects down towards the center of Earth.
Ground Reaction Force (GRF): The force exerted by the ground upward against gravity, counteracting it.

Friction Definition: The resistance that one surface or object encounters when moving over another.
Example of Friction in Sports:
- Golf Shoes/Cleats: Designed to increase friction, preventing slipping, and allowing players to plant their feet firmly.
- Pillowcase Example: Used under shoes to reduce friction for sliding purposes during exercises.
Friction Dynamics:
- Increased by compression: Added weight or pressure between two surfaces enhances friction.
- Decreased by traction: Using smooth surfaces or materials (like pillowcases) lessens friction and allows easier movement.

Linear Forces: Two or more forces acting along the same line. They can act in the same or opposite directions, all following a linear path.
Parallel Forces: Forces occurring in the same plane and same or opposite directions, often represented in diagrams to demonstrate their alignment.
Perpendicular Forces: Forces acting at a 90-degree angle to one another.

Brace Example: An example showing various forces (anterior, posterior) working to support a patient with a compression fracture. The alignment of these forces assists in standing upright.
Force Couples: A system where forces act in different directions yet produce motion.
- Example: A merry-go-round – two people pushing in opposite directions create circular motion.
- Scapular Motion: Involves upper trap, lower trap, and serratus anterior muscles working together to achieve upward rotation of the scapula.

Definition: Two or more forces acting on the same object but in different directions. They can be visualized as vectors creating a parallelogram shape, where the resultant vector represents the overall force acting on the object.
Deltoid Muscle Example: The anterior, posterior, and middle deltoids work together for shoulder abduction, showcasing how different muscle actions can lead to a common motion.

Traction Forces: Forces that create separation or distraction within joints. Seen when lifting heavy objects.
Compression Forces: Forces that push joints together, common during weight-bearing activities.
Shearing Forces: Result in a gliding motion of two surfaces. Excessive shearing can lead to injuries (strains or sprains).
Bending Forces: Involves compression on one side and traction on the opposite side, causing a bending effect around the joint.
Torsion Forces: Twisting forces that can result in injuries like spiral fractures if excessive stress is placed on a joint.

Velocity: The rate of change in position of an object, considering both magnitude and direction.
- Measurement: Typically expressed in units such as feet per second or miles per hour.
Acceleration: The rate of change of velocity, which involves both the speed and direction of an object.

Definition: A measure of the rotational force applied at a distance from an axis. It is the ability of a force to cause or increase rotation around an axis.
Calculation of Torque: Expression is given by $ext{Torque} = ext{Force} imes ext{Movement Arm}$ .
Movement Arm: The distance from the axis of rotation to the line of action of the force applied, crucial in understanding leverage in the body.

First Law (Law of Inertia): An object at rest stays at rest, and an object in motion continues in motion with the same speed and in the same direction unless acted upon by a net external force.
- Example: In a car, when the driver accelerates or stops, passengers are subject to inertia against their seatbelts.
Second Law (Law of Acceleration): The acceleration produced by a force on an object is directly proportional to the magnitude of the force and inversely proportional to the object's mass.
- Formula: $ext{Force} = ext{Mass} imes ext{Acceleration}$ .
- Example: Kicking a soccer ball will send it farther than a bowling ball due to the difference in mass.
Third Law (Action and Reaction): For every action, there is an equal and opposite reaction.
- Example: Jumping on a trampoline pushes down as the ground pushes back, facilitating upward motion.

Equilibrium: A state in which the sum of forces acting on an object is zero, resulting in no linear acceleration.
Center of Mass vs. Center of Gravity:
- Center of Mass: The point where the mass of an object is concentrated.
- Center of Gravity: The point where weight is balanced, usually near the center of mass unless influenced by external conditions (e.g., pregnancy).
Base of Support: Refers to the area beneath a person that includes all points of contact with the supporting surface.
- Stability Considerations: A person must maintain their center of gravity within their base of support to remain stable. Increasing the area of base support enhances stability.

Linear Motion: All parts move in the same direction and distance simultaneously.
Curvilinear Motion: Movement along a curved path, not circular.
Angular Motion: Movement around a fixed point (axis), where different parts of the body may move through different angles but the same direction and time.

Levers: Rigid bars that rotate around a fulcrum (axis). They can reduce the required effort to lift a load.
- Classes of Levers:
1. First Class Lever: The fulcrum is between the effort and the load. Example: See-saw, or the neck when nodding the head.
2. Second Class Lever: The load is between the fulcrum and the effort. Example: Wheelbarrow or standing on tiptoes.
3. Third Class Lever: The effort is between the load and the fulcrum. Example: Biceps during elbow flexion.

Pulleys: Systems that use wheels to change direction of force. They can be single fixed or moveable.
Inclined Planes: Ramps that reduce the effort needed to elevate objects, requiring less force over a longer distance.
- Formula for Inclined Plane: For an elevation of one inch, there should be twelve inches of ramp length, facilitating easier access to higher surfaces.