Linear Kinetics (Forces) Flashcards
What is Newton’s 1st law?
an object at rest or moving at a constant velocity at a straight line will stay that way unless acted upon by a external force
What is Newton’s 2nd law?
The acceleration of a body is proportional to, and takes place in the direction in which the force acts. It is also inversely proportional to the body’s mass
F = ma
What is Newton’s 3rd law?
- for every action there is an equal and opposite reaction
- for every force that is exerted by one body on another, there is an equal opposite force exerted by the second body on the first
What is friction?
- force that resists the sliding of 2 objects in contact
- vector quantity
- opposite of sliding potential
- parallel to surfaces in contact
What is normal force?
- vertical component (gravity) acts downwards
- ground reaction (normal) force acts upwards
What is friction force?
- horizontal component: acts parallel to surface
- opposite to applied force (and to potential sliding direction)
What is static friction?
2 surfaces are not sliding, but have the potential for movement
What are the 3 factors that affect static friction?
- texture of surfaces
- weight of block
- applied force
As friction increases, motive force needs to _____.
Increase
What is the coefficient of friction (μ)?
- the proportion of friction force resisting the sliding motion of the object to the normal force holding the objects together
- a constant for any 2 surfaces
- how difficult it is to move a given surface over another surface
How does texture affect static friction?
- grooves, scratches, and pores interlock/interact with texture on the other surface and impede motion
- the more interactions between the 2 surfaces, the higher the value of μ
What is the value of μ for a totally frictionless interaction?
0.00
What is kinetic friction?
- sliding surfaces
- grooves/pores “bumping”
What is rolling friction?
- occurs when 1 surface is rolling over another
- ## still depends on coefficient of friction and normal force
Coefficient of rolling friction is much ____ (less/more) than that of static of kinetic friction.
less
Rolling friction is actually a specialized case of ____ friction.
- static
- trying to avoid sliding, want to maintain static friction
What is the general term for a force that is perpendicular to friction?
Normal force
What are the 3 types of friction?
- static
- kinetic
- rolling
What is momentum?
- momentum of a body is a product of its mass and velocity
- momentum = mv
- vector quantity
What are the units for momentum?
kg m/s or Ns
What is the conservation of momentum?
- The total momentum of any given system will remain constant in the absence of any external forces
- the momentum prior to an action is the same as the momentum following the action
What is impulse?
- constant force (F) x time (t) is called the impulse of the force
- the impulse of a force is equal to the change in momentum which it produces
- relates to Newton’s second law
The best shock absorption technique is (relating to impulse):
decrease force over increased time (landings)
The best way for abrupt change of direction is (relating to impulse):
increase force over decreased time
The longer the time or larger the applied force, the ______ the change in velocity of body receiving force (duration of force application).
greater
Energy transfers are not 100% efficient. Where does this loss of kinetic energy (energy due to motion) go?
- sound
- heat
- absorption by deformation of the bodies involved
What are elastic collisions?
bodies involved separate after collision
What happens in a perfectly elastic collision?
momentum and kinetic energy is conserved
What are inelastic collisions?
- at least one body deforms
- bodies involved do not separate
What is elasticity?
the tendency of an object to return to its original shape once it has been deformed
What are the 2 classifications of elasticity?
- elastic impacts
- inelastic impacts
What is the degree of elasticity?
coefficient of restitution (e)
e is determined by…
- composition of the object
- composition of the surface of the object
- temperature
The value of e ranges from…
0 (inelastic) to 1.0 (perfectly elastic)
What are the 2 types of impacts to consider?
- direct
- indirect
What are direct impacts?
when objects collide head on
What are indirect impacts?
when objects collide at an angle
_____ impacts are the ones we most commonly encounter in sports.
indirect
For indirect impacts, the most important relationship to consider is that between the ______of ______ and ________. It is always measured from the _____.
- angles of incidence and reflection
- perpendicular
The angle of reflection depends on:
- the elasticity of the object
- the level of friction at the contact point
- the amount of spin on the object
What happens during direct contact?
outcome is usually spectacular and the deformation involves one or all of the colliding bodies
Define pressure.
force (F) distributed over a given area (A)
What are the units for pressure?
N per square m^2 or Pascals (Pa)
How should you decrease pressure for landing pads?
increase area
