Forces Flashcards
Will an unbalanced force always change the object’s speed? What about vel?
No on speed, yes on vel (think of ice skating with a rope around a point example)
Can an unbalanced force change object’s direction?
Not always (they can acc or dcc an object but object can still go in same direction)
Formula for torque
Tau = rFsin(theta) where r is the distance form pivot point, F is force (the whole ma or mg thing), and theta is angle b/w lever arm and force; units = N*m (as opposed to Joules because it doesn’t deal with work or energy); torque can be clockwise (NEG) or counterclockwise (POS) so if you want a torque system in equil —> clockwise and counterclockwise torque have to equal e/o
Formula for Fg/Fw
m * g; g = 9.8 m/s ^2
Formula for kinetic vs static friction
Kinetic f = mu_kF_N vs
static f = mu_sF_N; if you overcome static f (ie. Static f > mu_s*F_N) then the object will move and kinetic friction will take place)
Why is coeff of static friction > coeff of kinetic friction?
more contact points on object. It’s harder to move a stationary object than to move a moving object
How to find centripetal force and acc?
F = ma, a = v^2/r
A person falls with drag. If force of gravity > force of drag vs force of gravity = force of drag, what happens?
Acc downwards vs terminal vel (constant vel)
Units of Newton’s
KG*m/s^2
Newton’s law of gravitation
All forms of matter experience a force attracted to other Matter in the universe
F = (Gm1m2)/r^2; can only be pos
G is gravity constant 6.674E-11
If an object is in translational equil, what’s the sum of forces?
sumF=0
Translational equil vs rotational equil
When vector sum of all forces equal zero => first condition of equil vs when vector sum of all torques equal zero => second condition of equil
Translational vs rotational motion
Motion without rotation vs motion rotating around a fixed point
How does centrifugal force relate to Newton’s third law?
Centrifugal force is always anti parallel to centripetal force vector
How to find forces on inclined plane?
mgsin(theta) along incline with applicable friction opposite, mgcos(theta) perpendicular to incline with nml force opposite, gravity force straight down
How do you know if forces = action-rxn pair?
1) has to be same force
2) has to be equal in magnitude and opposite directions
3) has to act on diff objects
Mechanical advantage vs efficiency
Length of ramp/height; ratio of magnitude of force: force exerted on object by simple machine (Fout) to forced actually applied o simple machine (Fin) => Fout/Fin vs Wout/Win = (loadload distance)/(efforteffort distance)
Center of mass eqn
(m1x1 + m2x2 + etc…)/(m1 + m2 + etc…)
x = position; it’s sometimes based on where it is from relative center of mass or from pivot point (ex: if you have a 0.5 m long 2 kg stick, x will be 0.25 m)
Objects with higher mass generally have more inertia (ie. High resistance to change motion)
Yep, that’s Newton’s first law
Conservative vs nonconservative forces and examples of each
Forces that are independent from path and don’t dissipate energy, hence net energy = 0 (ex: gravity and electrostatic)
Forces that are path dependent and dissipate into energy like heat or thermal energy, hence some energy is lost (ex: friction, air resistance, viscosity); they’re not taken into account for mechanical energy eqn
Formula to find force in electric field
F = qE, where q = charge and E = electric field
no simple machine vs frictionless inclined plane vs frictionless pulley
F = mg, W = mg vs F = mg/2, W = mgh vs F = mg/4, W = mgh
