4 key principals

• Energy & Conservation of Energy

  • Energy calculations/transformations

• Work

  • W = Fdcosθ, = ∆E

  • Positive vs Negative Work

• Efficiency

  • Eff = W_o/W_i* 100% = E_o/E_i* 100%

• Newton’s Laws & Force Body Diagrams

  • Inertia, F = ma, Opposite and equal reaction

Energy & Conservation of Energy:

- Types of energy: Gravitational Potential, Kinetic, Mechanical, Solar, Thermal (etc)

• E_p = mgh ← work done against gravity

  • E = Joules (J), m = Mass (kg), g = Gravity (9.81 m/s²), h = Height (m)

• E_k = ½mv²

  • v = Speed (m/s)

• E_m = E_{p +} E_k

  • mgh + ½mv²

• E_mi = E_mf

  • E_{pi +} E_ki = E_{pf +} E_kf

- First Law of Thermodynamics/Conservation of Energy: Energy cannot be created or destroyed, only transformed from one type to another

- Conservation of Mechanical Energy: In an isolated system, all energy transfers are 100% efficient (nothing gets lost to friction, thermal, etc)

• Isolated, Closed, Open systems

  • No changes, energy changes, everything changes

- Transformations of energy in machines

• i.e.) Kinetic to Potential going up a hill on a bike

Work:

- A change in energy

• Positive vs Negative Work

  • Putting energy into the system (positive) or taking energy out of the system (negative)

- Calculated 2 ways, W = Fdcosθ or W = ∆E

• W = Fdcosθ

  • W = Work (J), F = Force (N), d = displacement or distance (m), cosθ = Angle of displacement (θ=0°=1, θ=90=0°, θ=180°=-1)

    • F = ma

  • Cannot be used when object is on angle other than 0, 90, or 180

• W = ∆E

  • W = E_f - E_i

    • Use when object on slants or when no specific force is given

Efficiency:

- A calculation of how much energy is lost to friction

• Eff = W_o/W_i* 100% = E_o/E_i* 100%

- Efficiency cannot be greater than 100% (Second Law of Thermodynamics)

• Can only be calculated using negative work

  • Positive work would result in percentage >100%

Newton’s Laws & Force Body Diagrams:

- Newton’s Laws:

• Inertia

  • Tendency of an object to resist change in motion (stay at rest or stay in motion)

  • More mass = more inertia

  • Not a force, rather a property of mass

• F = ma

  • a = acceleration (m/s²)

• Every action is met with an equal and opposite reaction (balanced forces)

  • Solid surfaces push back with equal force to what they are being pushed by

- Force Body Diagrams:

• Force Friction

  • Force that opposes motion (slows things down, usually points in opposite direction of Force Applied)

• Force Applied

  • Force caused by a outside push/pull, must be in direct contact with the object to be on diagram. Can be multiple

• Force Normal

  • Force exerted by solid surfaces, point perpendicular to surface object is resting on. Can be multiple

• Force Gravity

  • Force exerted by the earth. Always points straight down

• Force Tension

  • Force exerted by stress on objects (such as ropes). Can be multiple