Learn: KIN 321 Biomechanics Oregon State University Midterm 1 Terminology

Biomechanics

The study of forces and their effects on living systems

Mechanics

The analysis of forces and their effects

Kinematics

Description of motion

Kinetics

Deals with the forces that cause or tend to cause changes in motion

Intertia

The property of an object to resist changes in its motion

Mass

The measure of intertia

Weight

The measure of the force of gravity on an object

Force

A push or a pull, exerted an object

Internal Forces

Forces that act within the object or system whose motion is being investigated. Ex) Tensile, compression

Tensile Force

Pulling forces

Compression

The structure is under compression

External Forces

Forces that act on an objects as a result of its interaction with the environment surrounding it

Friction

The line of action parallel to two surfaces that moves or opposes movement

Static Friction

When friction acts between objects that are not moving

Dynamic Friction

Friction through movement, sliding past each other

Formula for Friction

Resultant Force

Result of vector addition between two or more forces

Net Force

Vector addition of all external forces acting on the object

Colinear Forces

Forces that have the same line of action

Concurrent Forces

Forces that do not act along the same line of action, but act through the same point

Weight Equation

W= mg

Static Equilibrium

If the object is either at rest, net force of zero or moving at constant velocity

Linear Motion

Also referred to as translation, when all points of the body are moving in the same direction, distance and at the same time. Two types: Rectilinear and Curvilinear

Rectilinear

Moving in a straight line with the same orientation, and distance. Ex) Coasting down a street on a skateboard

Curvilinear

Moving in a curved line, but the orientation of the object stays the same and distance Ex) Curveball pitch

Angular Motion

All points on a body or object move in circles about a fixed axis or line. Ex) Ballerina spinning

General Motion

Combination of linear and angular motion. Ex) Riding a bike. Upper body= linear, Legs pedaling=angular. (Most human motion is general)

Linear Kinematics

Describes linear motion using speed, distance and direction

Distance Traveled

Measure of a length that an object followed from beginning to end. Ex) following a trail up a mountain

Displacement

Straight line distance from beginning to end for an object. Ex) Going in a straight line in a helicopter from the bottom of a hill to the top, missing any curvy trails

Speed

Rate of motion/ rate of distance traveled, m/s

Average Speed

Distance object traveled divided by time to travel the distance.

Instantaneous Speed

Speed of an object at specific point in time

Velocity

Rate of motion in a specific direction, m/s

Average Velocity

Displacement of an object divided by the time it took for the displacement to occur

Instantaneous Velocity

Velocity at a specific point in time

Acceleration

Rate of change of velocity, m/s^2

Average Acceleration

Change in velocity divided by the time it took for it to occur( equation on acceleration previous slide)

Instantaneous Acceleration

Acceleration at a specific point in time

Uniform Acceleration

Net external force acting on an object is constant and unchanging

Projectile Motion

Motion of an object that is projected into the air or dropped and is acted on only by gravity and air resistance forces. Combines vertical and horizontal motion, they are independent of each other and follow the path of a parabola

Newtons First Law Of Motion: Inertia

Objects will stay at rest and objects in motion will stay in motion of no force acts upon them

Newtons Second Law: Acceleration

If a net external force is exerted on an object, the object will accelerate in the direction of the net external force. The acceleration will be directly proportional to the net external force and inversely proportional to its mass.

Net Force(sigma)= ma

Newtons Third Law: Action and Reaction

If an object exerts a force on another object, the other object exerts the same forces on the first object, but in the opposite direction.

Linear Momentum

Product of objects mass and linear velocity.

L=mv

Elastic Collision

Objects collide head on and momentum is conserved, objects will bounce off each other

Inelastic Collison

Momentum is conserved, but the colliding objects stay together after the collision and move together at the same velocity

Coefficient of Restitution

Essentially the bounciness of an object

Impulse

The product of force and time over which force acts

Impulse Momentum Relationship

Increasing and Decreasing Momentum

Increase time of force= increase momentum. Ex)Throwing in Track

Increase impact time= decrease momentum. Ex) Catching a baseball

Work

Product of force and amount of displacement in direction of that force, J.

U=F(d)

Positive Work

Force acting on object if object is displaced in same direction as force. Ex) Pushing up in a bench press

Negative Work

Force acting on object if object is being displaced in opposite direction of the force. Ex) Lower during a bench press

Energy

Capacity to do work

Potential Energy

Energy due to position. Two types: Gravitational and Strain

Kinetic Energy

Energy due to motion

Work- Energy Relationship

Work done by external forces(other than gravity) acting on an object causes an energy change of the object.

U= Change in Energy

Conservation of Mechanical Energy

Total mechanical energy of an object is constant if no external forces other than gravity act on object. Ex) Roller coaster

Not realistic because of friction

Power

Amount of work done in certain amount of time

P= W/change in time, Unit: Watts

Torque

Turning effect produced by a force. (Also called moment or moment of force). T= F x r

Centric Force

An external force directed through the center of gravity of an object

Eccentric Force

An external force not directed through the center of gravity of an object

Center of Gravity

Point in body where mass or weight is evenly distributed

Force Couple

A pair forces equal in size, but opposite in direction and not collinear, causes rotation. Ex) Rotator cuff

Net Torque

Torques acting around the same axis can be added or subtracted just like forces acting in the same direction

Stability

Capacity of an object to return to equilibrium or its original position after it has been displaced. Can be increased by, lowering COG, widen base of support, increasing weight/mass, increasing moment arm of objects weight and decreasing potential energy

Angular Kinematics

Describing angular motion

Angle

Intersection of 2 lines, 2 planes or a line and plane

Angular Position

Orientation of a line with another line or plane

Absolute Angular Position

If other line or plane is fixed and immovable relative to the earth

Relative Angular Position

If other line or plane is capable of moving

Angular Displacement

Change in absolute angular position experienced by a rotating line

Advantages and Disadvantages of Muscles

Must create a large force for modest loads, but also have a large range of motion

Angular Velocity

Rate of change of angular displacement

Average Angular Velocity

How long it takes for something to rotate through a certain angular displacement.

Instantaneous Angular Velocity

How fast something is rotating at a specific time

Angular and Linear Velocity Relationship

Average linear speed on a rotating object is equal to average angular velocity times the radius

Angular Acceleration

Rate of change of angular velocity

Tangential Acceleration

Component of linear acceleration tangent to the circular path on a rotating object

Centripetal Acceleration

Linear acceleration is directed toward the axis of rotation

Centripetal Force

Force causing Centripetal accelaration

Anatomical Position

Planes

Saggital, Frontal, Transverse

Axis

Anteroposterior, Transverse, Longitudinal

Sources: Crowell Lecture Slides and Biomechanics of Sport and Excercise. Third Edition. By Peter M. McGinnis