Lecture 2 Flashcards
Torque
Measure of a forces ability to cause acceleration
acting on a point besides center of mass
greater torque means greater rotational acceleration
What increases Torque
Force acting perpendicular
distance between point of application and point of rotation
T=Fl
(length lever)
Static equilibrium
velocities are zero
Equilibrium
no net force, no net torque. May be moving, but not accelerating
dynamic equilibrium
any velocities are non zero, but are constant - all forces balanced
Systems not in equilibrium
Center of mass accelerating translationally or other parts accelerating rotationally
sum of forces= MA
OR
F upward= F downward
ADD Ma to the side with less force
Open system
can exchange energy and mass with surroundings
closed system
exchange of energy- not mass- with surroundings
isolated system
no exchange of energy or mass with surroundings
Joule
1 J= 1 kg m^2 / s^2= 1 Nm
Mechanical energy
energy of a macroscopic system
Me= KE + UE
Kinetic energy
energy of motion
K= 1/2 mv^2
Types of potential energy
gravitational, elastic
Elastic potential energy
restorative elastic
Ue= 1/2 K X^2
Gravitational potential energy
Ug= mgh
Heat
energy transferred between a system and its surroundings due to temperature difference
Work
energy transferred for any other reason than temperature difference
equals change of energy
First law of thermodynamics
Any change in total energy of a system is due to work or heat
Energy is conserved
W + q= delta E total
W + q= Delta K + delta U
work energy theorem
W= delta K
energy transfer leads to change in kinetic energy
when work is done, energy changes
work equation
W= fdcos theta= delta K + delta U
When does energy go into a system
when work is done on it
Work is positive
When does energy go out of a system
when the system does work
work is negative
system transfers energy to surroundings which decreases its own energy
Power
rate of energy transfer
P= W/t or delta E/t
in watts or J/s
conservative force
when it does work on a system, the system experiences no change in mechanical energy
total work= zerp
law of conservation of mechanical energy
only when conservative forces are acting, the sum of mechanical energies remains constant
Hookes and gravity
conservation of mechanical energy equations
K1 U1 = K2 U2
0= delta U + delta K
How much work is done by gravity?
gravity is conservative, not part of the system
use FDcos theta
dont include GPE in delta U
non conservative forces
withdraw energy from a system
change total amount (mechanical energy)
W= delta K + delta U
mechanical advantage
reduce applied force using a machine
lever, ramp, pulley
