lab set #2 notes and ideas. energy work and power

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.