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Work W = Force * Distance F is always in the direction of motion and parallel. A Force can be exerted on an object, while no work is done.
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Lab Set #2Notes and Ideas
ENERGY WORK AND POWER
Work
•W = Force * Distance• F is always in the direction of motion and parallel.• A Force can be exerted on an object, while no work is done.
Energy • Kinetic = 1/2mv2
• Potential• due to gravity = mgh• Elastic = 1/2kx2 (also Known as Hooke’s law)
• Wnet = Change in Kinetic Energy
• WG = -Change in Potential Energy
Example
• A 1000kg Coaster moves from point 1 to 4. • A) What is the gravitational potential energy at 2 and 3 relative to 1?• B) What is the work done by gravity from start to finish?
Forces• Conservative Force – Work done does not depend on path
taken, but rather the initial and final positions. (Gravity)
• Nonconservative force – Depends on the path taken (Friction)
Equations To Know• Work Energy Principle
•WNC = ΔKE + ΔPE• Conservation of Mechanical Energy\
• Conservative Forces only
•KE2 + PE2 = KE1 + PE1
Energy
• Energy Cannot be Created or Destroyed simply transformed.
• When its seems we lose energy in a problem that is called a dissipative force and that is usually found in the form of Friction or Air resistance
POWER• Average Power = Work/ Time• Watt is the unit of power (1 Watt = 1Joule/s)• Horsepower = 550 ft*lbs/ s = 746 W
• Average Power = W/t F*d/t Force * Average Velocity = P
Efficiency e = Pout/ Pin
Momentum and Collisions
• p = mv
• Net Force = ma Δp/Δt
Momentum
• Impulse = FΔt
• Elastic Collisions (bounce off each other) Kinetic energies are the same before and after the collisions. So Energy and momentum are conserved.
• Inelastic Collisions (stick together) – kinetic energy is not conserved, it is transferred to a different form.
Collisions and Impulse
• Momentum Before = Momentum After• Elastic Collision - MaVa + MbVb = MaVa + MbVb
• Inelastic Collision - MaVa + MbVb = (Ma + Mb)Vab
Conservation of Momentum
• Momentum is still conserved, but is conserved in each direction.
• Pax + Pbx = P’ax + P’bx
• Pay + Pby = P’ay + P’by
Collisions in 2 dimensions
Optics
Reflection
Rough surfaces
Imaginary Image
Convex Mirror
F = r/2
Concave Mirror
Ray Diagrams• Step 1 – Principal Ray
Ray Diagrams• Step 2 – Central Ray
Ray Diagrams• Step 3 – Focal Ray
Mirror Equation
1𝑑𝑜
+1𝑑𝑖
=1𝑓
Magnification
•m =
Index of Refraction
• n = c = speed of v = speed in a given material
Snell’s Law
𝑛1𝑠𝑖𝑛 θ1=𝑛2𝑠𝑖𝑛θ2Angle of incidence
Angle of refraction
Power of Lens
• P=
Lensmaker’s Equation
1𝑓 =(𝑛−1)( 1
𝑅1+
1𝑅2
)
Simple Harmonic Motion
SHM
• In mechanics and physics, simple harmonic motion is a type of periodic motion where the restoring force is directly proportional to the displacement and acts in the direction opposite to that of displacement.
Hooke’s Law
• F = -kΔx
Circuits
Electric Current
• Definition - Any flow of charge• Symbol – I• Unit – Ampere = A = 1 C/s
• I =
Ground
• Definition – common conductor to which real circuits are connected to provide continuity in the circuit.
Ohm’s Law• Resistance – a measure of the degree to which conductor opposes
an electric current through it
• Voltage = Current x Resistance V=IR
• Unit = Ω = Ohm’s = 1V/A
•
Electric Power
• Power = = IV• Unit = Watt = 1 J/s
• P = IV I(IR) • P = IV (V/R)V
Series Circuit• Connected in a single path• Same Current through system• V =
Or
• V=IWhere:
Parallel Circuit• The source splits to
multiple paths or branches• Voltage is same
throughout the circuit• I =
• I = • Resistance in Parallel
Kirchhoff’s Rules
• Rule 1 – Rule of Junction – at any junction the amount of current in = the amount of current out.
• Rule 2 – Loop Rule – The sum of changes in potential around any closed path of a circuit must be ZERO.
How to solve using Kirchhoff
• 1. Label the currents and their directions• 2. Identify the unknowns• 3. Use the Junction rule• 4. Use the Loop Rule• 5. Solve the equations for unkown.