Physics Class 2 Flashcards
If circumference increases, what happens to:
1) Time?
2) Speed?
Time is the same
Speed increases too
With uniform circular motion, is speed and velocity constant?
Speed is consttant
Velocity is not
Centripetal acceleration
Ac = v^2 / r
Centripetal Force
Fc = (mv^2)/ r
Forces that act perpendicular to velocity _____ the speed, but ______.
Cannot change the speed
but can change direction
Torque
Force’s effectiveness at making an object spin/rotate
Torque formula
τ = rFsinθ
Units: N X m
Torque is maximized with sin90
OR (if you’re able to determine the lever arm):
τ = lF
l = rsinθ
In static equilibrium, what is the net torque and net force?
0 because it is motionless
What does ‘static equilibrium mean’?
Motionless, no net torque
Lever arm
shortest distance from the pivot to the line of action of the force
Fulcrum
Part that never moves
Work
Measures how much force contributes to the displacement of an object
W = Fdcosθ
Units: N x m –> Joules
- can be positive, negative or 0
When is work +, - or 0
Positive Work
0 < θ <90
Zero Work
θ = 90
Negative Work
90 < θ < 180
Conservative Forces
Gravity
- what goes in, comes out
What does work done by gravity depend on?
Initial and final height, does not matter about path taken to reach those heights
Power
Rate at which work is done
Formula:
P = W/t
Units: J/s –> N x m / s –> W (watts)
Power for a constant force parallel to a constant velocity
P = Fv
- v = d/t
Kinetic Energy
Ability to do work
Formula: 1/2 mv^2
Units: kg x (m/s)^2 = J
Total work done if no change in other forms of energy…
Wtotal = ΔKE
If work is positive = gains KE
If work is negative = loses KE
If work is 0 = speed is constant
Work done by gravity
Wgravity = mgh
= -ΔPE (losing PE, gaining KE)
Wgravity = -ΔPE (losing PE, gaining KE)
In any spontaneous process, potential energy decreases
When only conservative forces are doing work…
KEi + PEi = KEf + PEf
Conservative vs Non-Conservative forces
KEi + PEi + Wnc = KEf + PEf
Wnc = ΔE
Conservative:
- gravity, electrostatic force, spring force
- have PE associated with them
- if they’re the only forces doing work, mechanical energy is conserved
Non-conservative forces:
- kinetic friction, drag
- always do negative work
- if they’re doing work, mechanical energy is not conserved
Simple machines
Reduce the amount of force required to do something
- Pulleys
- Inclined Planes
Mechanical Advantage
Factor by which force can be reduced when using a simple machine
MA = Fresistance / Feffort
= normal / with machine > 1
Mechanical advantage > 1 because reducing amount of force by increasing displacement. Work stays the same
F = mg ---------------------> F = mgsinθ d = h ------------------------> d = h / sinθ W = mgh -------------------> W = mgh
Efficiency
Measures how much useful work was accomplished with the energy input
Efficiency (%) = Woutput / Energy input <100% (in real world, something is always lost)
