Forces

Question 1

Will an unbalanced force always change the object’s speed? What about vel?

Answer 1

No on speed, yes on vel (think of ice skating with a rope around a point example)

Question 2

Can an unbalanced force change object’s direction?

Answer 2

Not always (they can acc or dcc an object but object can still go in same direction)

Question 3

Formula for torque

Answer 3

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

Question 4

Formula for Fg/Fw

Answer 4

m * g; g = 9.8 m/s ^2

Question 5

Formula for kinetic vs static friction

Answer 5

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)

Question 6

Why is coeff of static friction > coeff of kinetic friction?

Answer 6

more contact points on object. It’s harder to move a stationary object than to move a moving object

Question 7

How to find centripetal force and acc?

Answer 7

F = ma, a = v^2/r

Question 8

A person falls with drag. If force of gravity > force of drag vs force of gravity = force of drag, what happens?

Answer 8

Acc downwards vs terminal vel (constant vel)

Question 9

Units of Newton’s

Answer 9

KG*m/s^2

Question 10

Newton’s law of gravitation

Answer 10

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

Question 11

If an object is in translational equil, what’s the sum of forces?

Answer 11

sumF=0

Question 12

Translational equil vs rotational equil

Answer 12

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

Question 13

Translational vs rotational motion

Answer 13

Motion without rotation vs motion rotating around a fixed point

Question 14

How does centrifugal force relate to Newton’s third law?

Answer 14

Centrifugal force is always anti parallel to centripetal force vector

Question 15

How to find forces on inclined plane?

Answer 15

mgsin(theta) along incline with applicable friction opposite, mgcos(theta) perpendicular to incline with nml force opposite, gravity force straight down

Question 16

How do you know if forces = action-rxn pair?

Answer 16

1) has to be same force
2) has to be equal in magnitude and opposite directions
3) has to act on diff objects

Question 17

Mechanical advantage vs efficiency

Answer 17

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)

Question 18

Center of mass eqn

Answer 18

(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)

Question 19

Objects with higher mass generally have more inertia (ie. High resistance to change motion)

Answer 19

Yep, that’s Newton’s first law

Question 20

Conservative vs nonconservative forces and examples of each

Answer 20

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

Question 21

Formula to find force in electric field

Answer 21

F = qE, where q = charge and E = electric field

Question 22

no simple machine vs frictionless inclined plane vs frictionless pulley

Answer 22

F = mg, W = mg vs F = mg/2, W = mgh vs F = mg/4, W = mgh