Physics 1: Kinematics & Newton Flashcards
Newton’s First Law (Inertia)
An object in motion at constant velocity or at rest will stay that way, unless acted upon by an external force.
Newton’s Second Law
F(net) = ma
Newton’s Third Law
F(AB) = -F(BA)
Force on X
Product of (mass of X) and (acceleration of X) F=ma
If you have a POSITIVE net acceleration, he normal force must be ( > or < ) m*g
Greater than (>)
Fill in the blank with: ( > ) or ( < )
If you have a NEGATIVE net acceleration, the normal force must be _______ m*g
Less than (<)
F(net) =
F(net) = F(N) - mg = m a(net)
Air resistance
Function of v^2 and k, where “k” is proportional to the density of air and the surface area of the mass.
Kinetic friction
f(k) =u(k)F(n)
Static Force: F(s)
F(s) = F(applied)
Fs(max)
minimum force required to get object to move = u(s)F(n)
Static and kinetic co-efficient relationship
µs is ALWAYS > µk
What forces are acting on a box at rest on an inclined plane
f(s) = f(applied) = mgsin(theta)
fs(max)=
u(s)mgcos(theta)
As the angle of an inclined plane (θ ) increases, what happens to the
a) applied force,
b) static force fs
c) MAXIMUM static friction (fs,max)?
As θ increases,
a) fapplied increases,
b) the static force increases
c) fs,max DECREASES
Gravitational Force
F= (Gm1m2)/r2
Two masses will exert an attractive force on one another inversely proportional to the square of the distance between them.
Uniform Circular Motion
The net force on an object moving at a constant speed on a circular path points toward the center of the circle.
F(centripetal)
F(c)=(mv^2)/r
Centripetal Acceleration
a(c) = v^2/2
Circumference of a circle
C = 2(pi)r Conversion: 2(pi)rad = 360 degrees
Theta of a circle (relation to arc length (s) and radius (r) )
theta= s/r
Angular speed (w)
2(pi)f = v/r
Torque
rotational analog of force is a vector Units: Newton meter (N*m) NOTE: Joules are (N*m) but scalar Torque= F*l l=(r)(sin(theta))
Torque rotational convention
Torque > 0: Counterclockwise Torque < 0: Clockwise
Rotational equilibrium
An object is in rotational equilibrium when the sum of the torques acting on it is zero.
Work
Work=Fd cos (theta) SCALAR unit: joules “transfer of energy” N*m = Joules
“Positive Work”
Work done on a system = transfer of energy INTO system. KE goes up
Energy
JOULES Kinetic Energy = (1/2)mv^2
Average Power (Watt)
Watt = Joules/second P=change in energy/change in time P= F*v
Work Energy Theorum
Work(net) = change in KE +work: gain KE -work: lose KE
How much work is done by F(Grav) in a satellite moving in a circular orbit?
Work in a circle: speed isn’t changing W(net) = change in KE = zero [although velocity IS changing bc the direction is changing, the SPEED is not. Speed is scalar)
Gravitational Potential Energy
U = mgh = F*d
Types of PE
1.Gravitational Potential Energy
- Elastic Potential Energy
- Chemical Potential Energy
4.Electrical Potential Energy
5.Nuclear Potential Energy
Conservation of Mechanical Energy
When conservative forces act on an object, its total mechanical energy is conserved. Work(cons force) = [(delta) KE - [(delta) PE)]
Conservative Forces: i) Is Mechanical energy conserved? ii) Is it path independent? iii) Examples
i) Yes, Mech Energy is conserved ii) Yes, it is path independent iii) Ex: Gravity, Electrostatic, Elastic
Non-Conservative Forces: i) Is Mechanical energy conserved? ii) Is it path independent? iii) Examples
i) No, mech energy is NOT conserved ii) NO, it is NOT path independent iii) Ex: friction, drag, pushing+pulling (pressure) (don’t forget energy lost to heat)
If you push a rock up a mountain, you raise its gravitational PE, but not its KE. Why does this not violate the Work-Energy Theorum?
Work(net) = Work(person put in) + Work(gravity) But W(person) is a non-conservative source added to the system. W(gravity) is a conservative source. Conservative forces only TRANSFER “funds”. They never make you richer/poorer. (ie: Checking=KE; Savings=PE) W(net) - W(cons) = W(noncons) (delta)KE - (-(delta)PE) = (delta)KE + (delta)PE = W(noncons)
Conservation of Linear Momentum
The total momentum of a system of objects is conserved as long as no external forces act on that system. Momentum = p= vector.
Inlastic Collision
- When a collision results in production of heat, light, sound, or deformation
As long as no external forces are present:
Conservation of Momentum:
m1v1 + m2v2 = m1v1 +m2v2
No Conservation of Kinetic Energy
KEi > KEf
because: KEi = KEf + Energy lost to heat or light
(1/2)m1v1i2+ (1/2)m2v2i2 > (1/2)m1v1f2 + (1/2)m2v22
Completely Elastic Collision
Conservation of Momentum:
m1v1 + m2v2 = m1v1 +m2v2
Conservation of Kinetic Energy
KEi = KEf
(1/2)m1v1i2+ (1/2)m2v2i2 = (1/2)m1v1f2 + (1/2)m2v22
Inelastic Collision
Conservation of Momentum:
m1v1 + m2v2 = m1va +m2v2
No Conservation of Energy:
KE(initial) = KE(final) + heat and deformation energy
Totally inelastic collisions
- objects collide and stick together rather than bouncing off of each other and moving apart
Conservation of Momentum
m1v1i + m2v2i = (m1+m2)vf
- Energy not Conserved:*
- KE(initial) = KE(final) + heat and deformation energy*
Two objects with equal masses are moving toward each other with the same speed. How do they move after the collision if the collision is (i) elastic? (ii) totally inelastic?
i) Velocities maintain same speed but switch directions ii) they stop: m1v1 + m2v2 = (m1 + m2)vf vf = zero. (so they stop)
Impulse
A force applied to an object over time causes a change in the object’s momentum called an impulse. I = (delta)p = F(avg)*(delta)t
Power
Work Energy Theorum
a direct relationship between the work done by all the forces acting on an object and the change in kinetic energy of that object. The net work done on or by an object will result in an equal change in the object’s kinetic energy
Efficiency
Mechanical Advantage
Hanging block by two strings
Two pulley system
Six pulley system
Center of Mass diagram
Center of Mass
Work, Energy Momentum
Essential Equations
