physics

• Inertia (1st Law of Motion)


  • Tendency of an object to remain in its state of motion
  • Moving objects have the tendency to stay moving
• Linear Momentum (p)


  • Vector that quantifies the motion of an object
  • Property of moving objects (linear in motion)
  • Momentum is directly proportional to the object's mass and velocity
  • Velocity and momentum of an object will always have the same direction
  • MOMENTUM IS INERTIA IN MOTION
• Momentum


  p = mv, kg m/s
• Change in Momentum (Δp)


  Δp = pf-pi, Δp= mvf- mvi
• Impulse


  • When an object interacts with another, the force is exerted on the other object over a certain period of time
  • Quantified by the impulse vector
  • Impulse is not a force
  • J = Ft, Unit = Ns
• Impulse-Momentum Theorem


  • When a force acts on an object during a certain time interval, the impulse of this force = the change in momentum of the object
  • J = Δp, FΔt = mΔv, 1 Ns = 1 kg m/s
  • Ft = fT
  • Is the change in p
  • Short period of time, then experienced force is stronger
  • Long period of time, then experienced force is weaker
• Force (2nd Law Motion)

  F = ma, kg m/s2
• When 2 things move at the same speed and collide with one another

  The one with the smaller size and lighter mass will suffer heavier damage
• Compared to soil and wood, water

  Will give less impact on an object because it allows more time for contact impulse during a collision: Water = soil < wood
• Energy


  • Ability of something to do work, which is the use force to change the displacement of an object
  • Exists in various forms
• Types of Mechanical Energy


  • Kinetic energy (motion)
  • Potential energy (stored)
• Kinetic energy (motion)


  • Energy in motion
  • m: mass (kg)
  • v: velocity (m/s)
  • unit: kg m2/s2 or J
  • KE = mv2/2 (Joule)
• Potential energy (stored)


  • Energy at rest due to its position
  • GPE = mgh (Joule)
  • Height it directly proportional to GPE
  • g = negative (-9.8 m/s2)
  • h= negative (m)
  • m: mass (kg)
  • unit: kg m2/s2, Nm, or J (Joule)
  • PE at its highest point = KE at its lowest point
• Law of Conservation of energy


  • Total energy in isolated system is constant
  • Can be observed in: Free fall, ideal pendulum, ideal rollercoaster
• Conservation of Mechanical Energy


  • GPE + KE = ME
  • (energy is transformed) = (total ME is constant)
• Energy and Work Relationship


  • Work done = GPE
  • This energy provides the object with the ability to do work
  • Work done = positive because it gains KE
  • To stop an object from moving, KE is lost (work done = negative)
  • GPE = mgh = work done on the object
  • KE = 1/2mv2 = work done to stop the motion of the body
  • KE + PE + work done against friction = 0
• Work Efficiency


  • Work done against friction is 1 of the factors that decreases the efficiency of the machines
  • eff. = work output / work input x 100%
• Work


  • W = Fd
  • F: force applied (N)
  • d: distance
  • Unit: Nm or J
• Heat


  • Form of energy that can do work (It can cause movement)
  • Heat -> Mechanical Energy
• James Presscot Joule


  English physicist and mathematician
• Units


  • W = work in Joules (J)
  • H = Heat in Calories (cal)
  • J = mechanical equivalent of heat = 4.186 joules/calorie (constant)
  • FORMULA: W=JH or W= (4.186)(H)
• Thermodynamics


  • "How does heat produce movement?"
  • The study of heat and its transformation to mechanical energy and vice versa
• Types of Heat Engines

  • Internal Combustion
  • External Combustion
• Internal Combustion


  • Burns the fuel inside the engine
  • Gasoline and diesel engines (cars)
• External Combustion


  • Burns fuel outside the engine
  • Steam engines (steam-powered trains)
• How do heat engines work?


  • Heat (HH) is supplied to the engine by an eternal source called hot reservoir (heat source)
  • The heat source is at temperature TH
  • The rest of the heat (HC) is released to an external place called cold reservoir or heat sink
• Internal Combustion Engine


  • Part of the energy supplied by the gasoline is transformed into useful work in moving car
  • Some of the energy heats up the car, the rest is given off as heat in exhaust gasses
  • The heat source is the gasoline and the heat sink is the surrounding air
• Thermal efficiency


  • Thermal efficiency = work ÷ input energy x 100
  • Symbol: Thermal efficiency = W ÷ Hh x 100
  • W = output work
  • HH = Input Energy (Hot reservoir)
  • HC = Output energy (Cold reservoir)
  • W = HH- HC
  • FINAL EQUATION: HH - HC ÷ HH X 100%
  • TE = W/HH X 100%
• Why is it impossible to get 100% efficiency from heat engines?
• Heat


  • Energy transferred from one body to the other due to temperature difference
  • Unit: Joule (J)
  • Commonly measured in calorie (Cal)
• Temperature


  • Degree of hotness or coldness of an object
  • Measure of average kinetic energy of molecules making up the object
  • Unit: Kelvin (K)
  • Commonly measure in degrees Celsius (C)
• Formula: H = mcΔt


  • H = MC (TF-TI)
  • m= mass (g)
  • c = specific heat (C)
  • tf= final temperature
  • ti = initial temperature
• Specific Heat Capacity


  • Specific heat, the quantity of heat required to raise the temperature of one gram of a substance by one Celsius degree
  • The units of specific heat are usually calories or joules per gram per Celsius degree
  • For example, the specific heat of water is 1 calorie (or 4.186 joules) per gram per Celsius degree
  • Different substances needed different amounts of heat to raise them through the same temperature interval
• Not all objects can be heated in the same degree
• Electricity


  Is electric current that is used as a power source
• Electric Current


  Is generated in a power plant, and then sent out over a power grid to homes, and ultimately to power outlets

  
• Michael Faraday discovered the flow of electric charges could be induced by moving a wire that contains electric charges, in a magnetic field. Thus, the generator was invented.
• Sources of Electrical Energy


  • Non-renewable Sources (More rapidly consumed that formed)
  • Renewable Sources (more rapidly formed or replenished than consumed)
• Non-renewable Sources


  • Nuclear energy - nuclear fission uses uranium to create energy
  • Fossil Fuels - Derived from remains of living organisms, Formed for thousands or even millions of years, Include coal, oil and natural gas
• Renewable Sources


  Hydropower, geothermal energy, wind power, biomass, and solar energy