Physics Unit 2 - Forces Flashcards
Fn
surface force
Ffr
force of friction (opposing motion)
Fap
Push/pull exerted by an object
Fg
Gravitational force (attraction between two objects)
Ft
Tension force pulled by a rope/string/chain
Balanced Force
A force with an acceleration or Fnet of 0
Either motionless or constant velocity
Unbalanced Forces
Forces act on an object. Fnet does NOT equal 0 and object has an acceleration
Newton’s First Law (Inertia)
If object is motionless, it stays motionless (unless moved by another force)
If object is in constant motion, object stays in motion (Unless an opposing force)
proportionality for Inertia and mass
Directly Proportional
Standing on a bus that suddenly moves [F]
Before= Object @ rest, stays @ rest
After= Another force pushes and person is “left behind”
Seatbelts
Car suddenly stops, car decelerates fast, but body wants to continue moving (inertia- 1)
Seatbelt gives external force that opposes inertia and decelerates body as car slowd down
Seatbelt mechanism
Moves constantly with the car
When it feels a pull [B], pedulum blocks spinner, locking the seatbelt in place
This makes it act as an external opposing force for the body
Headrest
Rear-end collisions: vehicle decelerates fast, inertia makes body continue [F]
Body strapped in by a seatbelt, head and neck have no support making it have an unnatural position (whiplash).
Headrest counter acts inertia by limiting heads movements during collision
Crumple Zone
Front of the Car “Crumple Zone” : absorbs impact of collision
Slows time it takes to stop the vehicle, applies less force on passengers
(2nd Law - a is inversely proportional to mass, directly proportional to Fnet)
Newton’s Second Law
Object will accelerate in unbalanced force’s direction
Fnet and A = DIRECT
Fnet and m = INDRECT
m and A = INDIRECT
How much is one Newton
1N = kg x m
———-
s^2
Newton’s Third Law
Positive Action = Negative Reaction
Friction
Horizontal forces that opposes motion of an object when two surfaces are in contact
Why does friction happen?
B/c of microscopic irregularities between two surfaces (IMF forces and “surface welds”)
Static friction (Fs)
opposes the start of motion (highest IMF and surface welds)
Kinetic friction (Fk)
Opposes movement of moving objects (lower surface welds)
Coefficient of friction (mew)
Constant ratio and %
ALways positive
Larger mew = more friction between surfaces,
opposite for smaller mew
proportionality for mew, Ffr and Fn
mew DIRECT Ffr
mew DIRECT Fn
Ffr DIRECT Fn
