Test One Chapter four Flashcards
what is force
something with the capability to cause a change in motion of a system
what are the properties of force
direction, orientation, magnitude, point of application, line of action
what is the law of inertia
a body at rest tends to stay at rest and a body in motion tends to stay in motion, unless acted upon by a net force
law of inertia explains the motion of a system in the absence of
net externally applied force
what is the law of acceleration
acceleration is proportional to the net force applied and inversely proportional to the mass of the object
equation for acceleration
force/mass
force equation
force= mass x acceleration
equation for momentum
mass x velocity
change in motion is directly proportional to the
magnitude of the net applied force
what is the law of action-reaction
to every action there is always an opposite and equal reaction
what are the four types of forces
non contact (field) forces, contact forces, external and internal forces, action and reaction forces
what is a field
any object possessing mass creates an invisible field of influence stretching throughout space
what is field force
non contact force
what is non contact force
newton’s law of universal gravitation explains the interaction of objects even when they are not in contact
what is strong nuclear force
occurs between subatomic particles; prevent the nucleus of an atom from exploding because of the repulsive electric force produced by its protons
what is electromagnetic force
between electric charges
what is gravitational force
exists between bodies of mass
what is contact force
the result of physical contact between two bodies
what is external forces
those that interact with the system from the outside
example of external forces
i hit ground, ground hits me
what are internal forces
act within the defined system
example of internal forces
muscles we use to apply the force, what muscles are engaged
what forces can change the motion of the system
external
what forces can change the shape of the system
internal
what is action force
“the force”, the initially applied force
what is the reaction force
the simultaneous equal counterforce acting in the opposite direction to the action force
what is the most pervasive external forces in everyday life
gravity
where is gravitational pull concentrated at
center of mass
what is weight
measure of the force with which gravity pulls upon an object’s mass
what happens to weight when you move closer to the center of the earth’s mass
weight decreases
what happens to weight when you move farther from the center of earth’s mass
weight increases
what is friction
force that resists the sliding of two objects in contact
friction exists when
two objects are in contact and have the potential to slide across each other
how do you represent the friction force in a vector
direction opposite of the potential sliding direction and parallel to the two surfaces in contact
what is normal force
force that acts downward on one surface and upward on another
examples of normal force
weight or gravity acting towards the center of the earth, force that presses two surfaces together
what is ground reaction force
oppositely directed normal force
what is static friction
exists when two contacting surfaces are not currently sliding relative to each other but do possess the potential for movement
in order for object to move what must happen
applied force must be greater than the static friction
what factors affect static friction
normal force, coefficient of static friction, static friction force
what is static friction force
force that must be exceeded to start the slide of the object
what is equation for static friction
normal force x coefficient of static friction= static friction force
gravity equals
9.8 m/s^2
normal force equation
= mass x gravity
what is kinetic friction
friction in cases when the two surfaces are already sliding relative to each other
kinetic friction occurs when
you are moving
the coefficient of kinetic friction is ____ than the coefficient of static friction
lower due to the surface molecules are not locked together instead they are just bumping into each other
equation of kinetic force
normal force x coefficient of kinetic friction= kinetic friction force
is static force variable or constant
variable bc you have to apply greater amount of force go from static to moving
is kinetic force constant or variable
constant and the energy used is lower
why would it be more tiring to push sled and stop instead push sled at slow continuous rate
takes more energy and force to over come the static friction where in kinetic friction the force is constant
what is rolling friction
exists whenever one surface is rolling over another but not sliding
compare coefficient of rolling friction to kinetic and static
less than both
what is pressure
the magnitude of applied force acting over a given area
equation of pressure
= force/ area
what are the units of measure for pressure
newtons/ meters ^2
what is motive force
a force that tends to lead to a change in motion in the form of increased velocity or change in direction of the system
what is resistive force
tends to prevent changes in motion by other external forces or decrease the velocity of a system that is already in motion
what are examples of resultant forces
motive, resistive, centrifugal, centripital
what is centripetal force
any force that causes a system to exhibit circular motion, center seeking
what is centrifugal force
the force that is equal to and opposite the centripetal force, throws things to the outside to separate them
applied forces can come in the form of
push or pull
in musculoskeletal system, internally applied forces are often
pulls
in musculoskeletal system, externally applied forces are
pulls and push
what in the body, internal forces, resist deformation
ligaments
what is stress
the external force acting to deform material
what is the equation of stress
= force/ area
what is stress’ unit of measurement
N/m^2
stresses causes what in tissues
deformation
what are the types of stress
compression, tension, shear, bending and torsion
what is compression of stress
result of two forces being applied to the system in opposite directions toward to each other, push toward center from both sides
what is tension stress
occurs when two forces are applied to a system in opposite directions away from each other
what is shear stress
occurs due to application to two parallel forces that tend to simultaneously displace one part of a system in a direction opposite another part of the system
what is bending
occurs when two off-axis forces are applied such that tension stress is caused on one side of the system and compression stress occurs on the other side
what is torsion
cause by two forces being applied in such a way that part of the system is rotated arounds its longitudinal axis in a direction opposite rotation of another part of the system, shear and twisting at same time
what is strain
the resulting magnitude of deformation as a result of the applied stress, the percentage change in length due to an applied stress
strain and stress
strain is how much it changes from the stress applied
what is the equation for strain
= change in length/ initial length
strain is proportional to
stress
what is elastic modulus
relationship of stress and strain for a given material and type of deformation
what is the equation of elasticity
= stress/ strain
what is the elastic region
the linear portion of any given stress/strain given, the material will return to its original shape if the tensile stress is removed within its range
what is the yield point in elasticity
point at which the applied stress can lead to permanent deformation
what is the plastic region of elasticity
non linear response of the material after the yield point, breaking point where tissue will fail, some degree of deformation will persist after removal of the stress
what is the coefficient of restitution
parameter observed after reformation that indicates the ability of an object to return to its original shape after deformation
what is the value of perfectly inelastic
0.00
what is the value of perfectly elastic
1.00
what are the two types of forces exerted by fluid on a system
force due to being submerged in fluid, force due to moving through a fluid
what is buoyant force
the vertical, upward- directed force acting upon an object that is submerged in a fluid
what are the two components in buoyant force
pascal’s law and pressure increases in large increments with relatively small changes in depth
what is pascal’s law
pressure is same in all fluid, and when pressure changes in fluid it is transmitted throughout the fluid
what is archimedes’ principle
a body submerged in a fluid will be buoyed up by a force that is equal in magnitude to the weight of the displaced water
what is dynamic fluid force
acts upon a system that is moving through a fluid, system applies force to fluid particles which moves them along the outside of the system
what is the law of attraction
every particles attracts every other particle in the universe with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers
example of non contact force
magnets, gravity, protons with electrons and neutrons
example of contact force
tackle in football, ball to bat, foot to soccer ball
what can change the motion of the system
external force
what can change the shape of the system
internal forces
what is an example of an action-reaction force
you push the ground and the ground pushes back
what friction produces the greatest resistance to a change in motion
static friction
what direction does the friction force act in relation to the applied force
opposite
what is the relationship between the normal force and force of gravity
equal to each other but in opposite directions
example of pressure
Wearing a high heel that decreases the surface area of the heel and can cause greater pressure on a surface such as a floor causing a mark or you can wear heels that are flat with more surface area causing less pressure to be applied from the heel to the floor
strain is proportional to
stress
