Chapter 2 Flashcards
force
an interaction of some sort that can cause an object to accelerate
units for force
Newton (N) = SI unit
N = kg•m/s2
gravitational force
this force acts on mass at a distance
electromagnetic force
most likely to appear in electrostatic problems
contact/pushing force
force you can exert by pushing an object horizontally
normal force
the force that surfaces exert in response to gravity
friction
the force that pushes back against horizontal movement
tension
the force exerted on an ideal string
centripetal force
any force that makes an object follow a curved path
force applied to strings
Hooke’s law (F = -kx)
Newton’s first law
statment about inertia
within a reference frame, an object remains at rest or at a constant velocity unless an external force acts upon it
Fnet = 0 at equilibrium
Newton’s second law
defines force
Fnet = m•a
Newton’s third law
how forces come in pairs
Every action has an equal and opposite reaction
Fab = -Fba
free-body diagram
representation of all the forces acting on an object
center of mass using reference point when more than 1 mass is being studied
xcenter= m1x1 + m2x2…/ m1 + m2…
static friction
applies when we are pushing an object and it doesn’t move because the applied force is less than a threshold that is defined as Fmax= µsNs where µs is the coefficient of static friction and N is the normal force of the object
Fapplied less than or equal to Fmax
kinetic friction
once the object is put into motion Fmax is greater than Fmax (=µsN)
kinetic friction is a specific property of the material an object is made out of and the surface an object is sliding across
remains constant as the applied force increases and is present if the applied force suddenly stops
Fkinetic= µkN
air resistance (drag)
opposes the direction of the objects motion
affected by density of the air, velocity of the object, cross-sectional area of the object, and a drag coefficient’eventually drag will equal the force of gravity so it can no longer accelerate = terminal velocity
box on incline plane
F = ma
force of gravity between 2 objects
Fgrav= G(m1m2/r2)
centripetal acceleration is
a = v2/r
Fc = mg = mv2/r which simplifies to g = v2/r
Hooke’s law
Fspring= -kx
k is the spring constant and is unique for each spring and has units of N/m
greater k units mean that more force is necessary to deform a spring by a certain amount = stiffer
torque
t= F•d•sin(theta)
torque refers to rotational force. caused by force applied to a lever arm at a certain distance from an object capable of rotating around a fulcrum
3 ways torque can be increased
increased force, increased distance from the fulcrum, and as close to 90 degrees as possible
direction of torque
Counterclockwise is the positive rotation direction of torque
clockwise is the negative direction of torque
energy
what accomplishes work
work is defined in units of
Joules
1 J =
N•m (1 Newton of force applied across 1 meter)
1N = 1kg•m/s2 then 1J =
1 kg•m/s2/s2
work is a what kind of quantity
vector quantity
Work =
F•d•cos(theta)
- occasions where sine will be used
conservative forces
- path independent
- the amount of work done by a conservative force does not depend on its path
- care about displacement for conservative forces
types of conservative forces
- graviation
- electromagnetic forces
- spring forces
non-conservative forces
- exacting a certain energetic cost per distance
- path-dependent
types of non-conservative forces
- air resistance
- friction
work = force • distance only works for?
- constant forces
area under the curve of a force vs displacement graph =
work
for ramps, the ideal mechanical advantage can be calculated by:
MA = length of incline/ heigh of incline
Fin • din =
Fout • dout
Power
work divided by time
units of power
Watts = J/s
work also equals
P • (deltaV)
idea of power is?
- essentially that a given amount of work could be expended either quickly or slowly, and that a system capable of doing so quickly is more “powerful”
Power also equals
F•v (velocity) and can be applied to situations where energy must be applied to keep an object travelling at a certain velocity despite the presence of a force opposing that motion, such as friction
