EXS 322 Biomechanics
Force is a ____ or ____
Push or pull
Forces are exerted by ____ on other _____
objects on other objects
Forces come in ____
pairs; action & reaction
The force exerted by one object on another is matched by an ____ but ____ directed force exerted by the ______
equal but oppositely, second object
A force is something that ____ or ______ an object
accelerates or deforms
In rigid-body mechanics, we ignore ______ and assume that the objects we analyze do not _____
deformations, change shape
In rigid-body mechanics, objects do not _____ but they do _____ if the force is _____
deform, accelerate, unopposed
Mechanically speaking, something accelerates if it ____, _____, _____, _____, or ______.
starts, stops, speeds up, slows down, or changes direction
Our most familiar unit of measurement for force is the ____, but the SI unit of measurement for force is the _____
The newton is abbreviated as _____
One newton of force is defined as the force required to accelerate a
1.0 N = (1.0 kg)(1.0 m/s^2)
1 kg mass 1 m/s^2
One newton of force is equal to ____lb of force, or 1lb equals _____ N
.225lb, 4.448 N
To fully describe force, you must describe its ___ and ____
size and direction
Internal forces are forces that act within the object or system whose motion is being investigated. Internal forces hold things together when the structure is under tension or compression. Sometimes the tensile or compressive forces acting on the structure are greater than the internal forces of the structure can withstand. When this happens, the structure breaks. Structural failure in the body occurs when muscles pull, tendons rupture, ligaments tear, and bones break.
If pulling forces act on the ends of an internal structure, the structure is under tension and this is tensile force.
If pushing forces act on the ends of an internal structure, the internal pushing forces are referred to as compressive forces, and the structure is under compression.
Internal forces cannot produce any changes in the ____ of the _________
motion of the body's center of mass
External force are forces that act on an object as a result of its interaction with the environment surrounding it.
External forces can be classified as either ____ or ______ forces
contact or non-contact
Contact forces occur when ____
objects are teaching each other
Non-contact forces occur ___
even if objects are not touching each other.
Give an example of non-contact force:
gravitational pull of the earth.
The force of gravity acting on an object is defined as the _________-
_____ is the force of gravity acting on an object
weight of the object
Gravitational acceleration/acceleration due to gravity - abbreviated as g
9.81 m/s^2 or 32.2 ft/s ^2
W = mg
W = weight (newtons
m = mass (kg)
g = acceleration due to gravity = 9.81 m/s^2
Objects in contact with each other (contact forces) can be either _____ or ______
solid or fluid
Fluid contact forces
air or water resistance
Acts between the non-lubricated surfaces of solid objects or rigid bodies in contact and acts parallel to the contact surfaces.
develops between two layers of fluid and occurs when dry surfaces are lubricated.
Friction arises as a result of interactions between ______ of the ____ in contact
molecules of the surfaces
When dry friction acts between two surfaces that are not moving relative to each other.
When describing the maximum amount of friction that develops just before two surfaces begin to slide.
Dynamic friction/sliding friction/kinetic friction
When dry friction acts between two surfaces that are moving relative to each other.
Dry friction is not affected by the ___ of the _______ in contact
size of the surface area in contact.
Friction opposes ______ between the surfaces in contact
relative motion or impending relative motion
Friction is proportional to the ________ pushing the ________
normal contact forces, two surfaces together
As normal contact forces increase, _________ increase as well
as normal contact forces increase, the frictional forces increase as well.
Friction is affected by the _________ in contact
characteristics of the surfaces in contact
Greater friction can be developed between _____ and ______ surfaces than between ______ and _______ surfaces
softer and rougher surfaces than between harder and smoother surfaces.
______ friction is greater than ______ friction
static friction is greater than dynamic friction
The net force acting on an object is the sum of all the external forces acting on it. The net force is the vector sum of all the external forces. The vector addition of all the external forces acting on an object.
Forces are added using the process of _____
The result of vector addition of all the external forces acting on an object
Collinear forces are forces that have the same line of action.
Forces can be added using algebraic addition only when
forces act along the same line and in the same direction
If forces do not act along the same line but do act through the same point.
the study of forces and their effects on living systems.
Sport and exercise biomechanics
the study of forces and their effects on humans in exercise and sport.
The ultimate goal of sport and exercise biomechanics is
performance improvement in exercise or sport.
the length of the side of the triangle opposite of the angle theta
Adjacent refers to
the length of the side of the triangle adjacent to the angle theta
Hypotenuse refers to
the length of the side of the triangle opposite the right angle
Sin refers to
Cos refers to
Tan refers to
Mnemonic for Sin (theta)
Some of his
Mnemonic for Cos (theta)
Children Are Having
Mnemonic for Tan (theta)
Trouble Over Algebra
If an object is not moving, it is in _____ equilibrium.
In static equilibrium, acceleration is ____, and the sum of all external forces acting on the object is ____.
net external force or vector sum of the external forces
The sense of a force or any vector is the
direction in which the arrow of the force or vector points along its line of action.
Net horizontal force
Horizontal component of the net external forces
Net vertical force
Vertical component of the net external forces.
Forces are vector quantities meaning they are
They are vector quantities, so they are described by a size and a direction of action.
Internal forces hold things together and cannot cause
Internal forces hold things together and cannot cause changes in the motion of a system.
External forces may cause
External forces may cause changes in the motion of the system.
The most commonly felt external forces are
The most commonly felt external forces are gravity and contact forces.
Friction and the normal reaction force are the
Friction and the normal reaction force are the two components of a contact force.
If the net external force acting on an object is zero, the object is
If the net external force acting on an object is zero, the object is standing still or moving in a straight line at constant velocity.
If the object is standing still, it is in a state of
If the object is standing still, it is in a state of static equilibrium, and the external forces acting on it are balanced and sum to a net force of zero.
If the external forces acting on an object do not balance (i.e., they do not sum to zero), the object is
If the external forces acting on an object do not balance (i.e., they do not sum to zero), the object is not in equilibrium and will change its state of motion.