Newtonian Mechanics Flashcards
What are the SI units for Force?
Newton (kg*m)/s2
What is the difference between mass and weight?
mass= kg (scalar and indep. of gravity)
weight= Fg=mg= N (vector)
Newton’s 1st Law
A body in motion will stay in motion and a body at rest will stay at rest unless acted upon by an outside force
Newton’s 2nd Law
F=ma
Newton’s 3rd Law
For every action there is an equal and opposite reaction
FBA (on A from B) = - FAB (on B from A)
(ie. rockets)
Gravity
F=(Gm1m2)/r2
- weakest of 4 forces
- always attractive
Torque
Torque=rFsinØ
Torque=r†F
- application of force at some distance (lever arm) to fulcrum
- Torque is measured in N*m not J
Centripital Force/ accel
Fc=(mv2)/r
ac=v2/r
- Fc is force necessary to keept an object of mass, m, in orbit with radius, r
- when Fc no longer working on an obj, objcect will assume tangential pathway
- Fc always directed towards center of circle
frictional force
- always opposes an objects motion
static friction
Fs=Fapplied
Fs, max=μsFn
kinetic friction
Fk=μkFn
- kinetic friction is a constant value, whereas static friction is not
which is always greater μs or μk?
μs
- therefore, Fs, max will always be greater than Fk
Translational equilib
- vector sum of all forces in x and y direction acting on an obj is zero
- therefore no accel, constant motion (could be non-zero velocity just constant)
Rotational Equilib
- vector sum of all torques acting on an object is zero
- “clocks are negative” CW= - CCW= +
- choose pivot point in order to eliminate a torque
Do you weight more or less when going up in an elevator?
What about when the elevator is going down?
- Elevator going up: You weigh more on an elevator accelerating up because F=mg + ma, where a is the acceleration of the elevator (same as elevator decelarating on way down)
- You weigh less on an elevator accelerating down because F=mg - ma, where a is the acceleration of the elevator (same as elevator decelarating on way up)
What is the component of gravity going down an inclined plane?
“sin slide”
In a non-moving object on an inclined plane: normal component of gravity = normal force; parallel component of gravity = static friction
In an obj going down an inclined plane at constant velocity, is the parallel component of gracvity equal to, less than, or greater than the kinetic friction?
- What about when obj begins to slip down plane?
- What about when obj accel. down plane?
- When push an obj up a plane what forces are you overcoming?
Parallel component of gravity = kinetic friction
(b/c constant velocity = no acceleration = no net force)
- object that begins to slip on the inclined plane: parallel component of gravity > static friction
- object that accelerates down the inclined plane: parallel component of gravity > kinetic friction
- When you push an object up an inclined plane, you need to overcome both the parallel component of gravity and friction.
What are the four forces in order of strength?
- The strong force (nuclear force) is the strongest force, but only acts at subatomic distances-binds nucleons
- Electromagnetic force: acts at observable distances. Binds atoms together. Allows magnets to stick to your refrigerators. Responsible for the fact that you’re not falling through chair right now
- Weak force: Responsible for radioactive decay
- Gravity: Responsible for weight (not mass!) and planet orbits
How does the Fs change as Ø increases (for a box on an incline)?
Fs=Fapplied=mgsinØ
therefore as Ø increases, Fapp increases so Fs increases
(easier to start moving on a steep slope, harder to start moving on a shallower slope)
MISTAKE is that Fs,max=mgcosØ so then as Ø increases, Fs,max decreases
g = ?
g= Gme/re2
Fg=Gmem/re2
- two masses exert an attractive force invserly proportional to square of dist b/w them
Uniform cicular motion
frequency
What is the relationship b/w KE and frequency in uniform cicular motion
