Forces Opposing Motion Flashcards
forces opposing motion
high velocity in air
movement through water
gravity
friction
force that occurs when an object moves while in
contact with an object
with two fluids
types of friction
sliding
rolling
static
sliding friction
2 surfaces in contact slide past one another
when walking
limiting friction
friction force required to overcome inertia
equals normal reaction x constant (depending on surface)
F = μ x R
F = friction force
μ = coefficient of friction (depends on hardness and roughness)
R = reaction force (normal) (perpendicular to surface of contact
(doesn’t say anything about surface area)
contact area
pressure,
friction in the human body
increased heat production, damage and wear to tissues
synovial fluid
smooth articular surfaces
bursae, blisters
rolling friction
resistive force, spherical object rolls
depends on diameter, surfaces, normal force
ranking of friction forces
static > sliding > rolling
applying brakes
want to maximise static friction as it has limiting friction, therefore when applying brakes you want to pump them and don’t let them lock up otherwise sliding friction is being used and that’s not wanted.
physical properties of striking equipment
rotational inertia, centre of percussion
COP
below COG
point where the translation of the forward = + opposite to the rotation of the bat backwards?
no oscillation or vibration
maximum distance, all of the bats velocity is transferred to the ball
therefore we want to make the COP as large as possible
variants of the COP
more mass toward the bottom of the bat = COP lower
elasticity
regain original shape
falling ball hits ground (elasticity)
GRF compresses ball, until COG stops its downward motion, deformed, elastic energy
ball recoil causes bottom surface to push against ground, generating GRF that moves ball upwards
coefficient of restitution
measure of elasticity when striking a surface + ability to reform
larger the coefficient = more elasticity
factors affecting coefficient of restitution, in relation to more temp, P and softness (ground)
more P = More elasticity
more softness = less rebound (ground)
more temp = More elasticity
velocity before impact, formula
u1 = (2gH d) square root u1 = velocity before impact g = gravity H = height dropped
direct + oblique impact
either head on or perpendicular
Angle of approach + angle of rebound
horizontal (AR)
vertical
angle of incidence
angle of reflection
Rebound- topspin
grips (accelerates) and stays lower
V(L) is high + V(R) is low, decreased friction effect, doesnt lose that much forward speed
V(L) is low + V(R) is high, gain speed on bounce
Rebound- backspin
higher and slows down on surface, GRF is greater, therefore greater friction, slows down