Physics - Energy & Power

Energy & Power

Forms of Energy

• Nuclear: Energy stored in the nucleus of an atom, released during nuclear reactions in fission or fusion.
• Solar: Energy from the sun, harnessed through various technologies such as solar panels.
• Coal: A fossil fuel derived from ancient organic matter, primarily used for electricity generation and heating.
• Oil: A fossil fuel used for transportation, heating, and electricity generation.
• Natural Gas: A fossil fuel primarily composed of methane, used for heating, electricity generation, and as an industrial feedstock.
• Wind: Kinetic energy harnessed from wind currents, converted into mechanical energy using turbines.
• Water (Hydropower): Potential energy from stored water converted into mechanical energy through dams or water turbines.
• Biomass: Organic material used as fuel, either directly or converted into biofuel, derived from plants and animals.

Objectives

1. Define energy.
2. Identify various forms of energy.
3. Describe energy transformations in given situations.
4. Apply the relationship: work = force x displacement.
5. Discuss the use of energy from alternative sources and its importance to the Caribbean.

Definition of Energy

Energy is defined as the ability or capacity to do work. It exists in many forms, which can be categorized into two main types: Potential Energy and Kinetic Energy.

Potential Energy (Ep)

• Potential Energy is the energy a body possesses due to its position or condition. It is stored energy that has the potential to do work based on factors like height and configuration.

Kinetic Energy (Ek)

• Kinetic Energy is the energy a body has due to its motion. The equation for kinetic energy shows that it is directly proportional to the square of its speed:
  $E_k = \frac{1}{2}mv^2$
  where m is mass and v is velocity.

Types of Energy Stores and Systems

• Gravitational Energy: Energy stored in an object due to its height above the Earth.
• Elastic Energy: Energy stored when an elastic object is deformed under force.
• Chemical Energy: Energy released from breaking chemical bonds, crucial for metabolic processes.
• Electrical Energy: Energy generated by the flow of electric current.
• Sound Energy: Energy produced by vibrating objects, manifesting as sound.
• Magnetic Energy: Energy associated with magnetic fields and the relative positioning of magnets.
• Electromagnetic Energy: Energy transmitted through electrical and magnetic waves, which can travel in a vacuum.
• Thermal Energy: Energy resulting from the movement of particles within an object or system, contributing to temperature.
• Nuclear Energy: Energy released during nuclear fission or fusion, processes that involve splitting or combining atomic nuclei.

Energy Transformations

Cooking Food in a Microwave Oven

1. Electrical Energy: Powers the microwave.
2. Electromagnetic Energy (Microwaves): Generated to cook food.
3. Thermal Energy: Increases the temperature of the food.
   • Description: The transformation demonstrates how electrical energy is converted into electromagnetic energy, which then transforms into thermal energy.

Vehicle Coming to Rest

1. Chemical Energy: Released during the combustion of gasoline.
2. Kinetic Energy: Present as the car moves.
3. Thermal Energy: Generated from friction between brake pads and drums during stopping.
   • Note: Thermal energy is always a product or by-product of energy transformations.

Work Done

Work is performed when a force causes the motion of an object. Thus, if a person pushes against a wall and doesn’t move, work hasn’t been done, even though they may exert effort.

• Formula:
  $W = F imes d$
  where W is work, F is the force parallel to the displacement, and d is the displacement.
• Units: The unit for work is Newton-meter (Nm), equivalent to Joules (J).

Work with Angle

• When force is applied at an angle, the equation modifies to:
  $W = F imes d imes ext{cos}( heta)$
  where Θ is the angle between the force and the displacement direction.

Example Calculation of Work

1. Scenario:
   • For a force of 500 N over a distance of 6 m:
     $W = 500N imes 6m = 3000 Nm$
   • For a force of 500 N with 0 m displacement:
     $W = 500N imes 0m = 0 Nm$
   • Conclusion: If there is no displacement, no work is done.

Problem Solving

1. Calculation of Work Against Gravity:

   • If a cyclist with a mass of 70 kg (bicycle mass 7 kg) ascends to 2100 m, using $g = 10 N/kg$:
     $F = mg = 77 imes 10 = 770 N$
     $W = F imes d = 770 N imes 2100 m = 1617000 Nm = 1617000 J$

2. Walking Up an Incline:

   • A man of mass 60 kg walks up a track inclined at 38° for 210 m:
     $F = mg = 60 imes 10 = 600 N$
     $W = F imes d imes ext{cos}(38°) = 600 imes 210 imes ext{cos}(38°) = 99289J$

Energy Use in the Caribbean

• Jamaica and Natural Gas: Many Caribbean nations like Jamaica depend on natural gas for electricity, a non-renewable source.
• Alternative Energy Sources: There's a question of whether Jamaica could benefit from alternative energy sources, prompting students to analyze three potential sources for better sustainability and energy security.

Potential Energy (Ep) and Calculations

Definition of Potential Energy

• Potential energy refers to the energy stored as a result of an object's position.
• Example: A demolition ball raised high has stored potential energy.
• Formula for Gravitational Potential Energy:
  $PE = mgh$
  where m is mass, g is gravitational acceleration, and h is height.

Calculation Example

• For a loaded cart with mass 3.0 kg at height 0.45 m:
  $PE = (3 kg) imes (9.8 m/s^2) imes (0.45 m) = 13.2 J$

Kinetic Energy (Ek) and Calculations

Definition of Kinetic Energy

• Kinetic energy is the energy of motion, where the energy depends on the mass and speed of an object.

Calculation Examples

1. Determine kinetic energy for a 625 kg roller coaster moving at 18.3 m/s:
   $KE = 0.5 imes 625 kg imes (18.3 m/s)^2 = 1.05 imes 10^5 J$

   • If speed doubles, kinetic energy increases by a factor of four due to its quadratic relationship with speed.

2. Calculate Missy Diwater's speed before hitting the water with a kinetic energy of 12,000 J and mass of 40 kg:
   $12,000 J = 0.5 imes 40 kg imes v^2$
   Solving yields $v = 24.5 m/s$

Power

Definition of Power

Power is defined as the rate at which work is done or energy is transferred.

• Measurement Unit: Power (P) is measured in Watts (W), where 1 W = 1 J/s.

Example Calculation

1. Work done by motors lifting a 2N weight through a height of 10 m:
   For motor one:
   $W = F imes d = 2N imes 10m = 20J$

   Time taken by motor one = 5s, thus:
   $P = \frac{W}{t} = \frac{20J}{5s} = 4W$

   For motor two with the same work done in 10 seconds:
   $P = \frac{20J}{10s} = 2W$

   • Conclusion: Motor one is twice as powerful as motor two.

Efficiency

Definition of Efficiency

Efficiency refers to how well a device converts energy input into useful energy output, expressed as a ratio or percentage.

• Efficiency cannot exceed 100% as that would imply creating energy, violating the law of conservation of energy.

Examples of Energy Waste in Appliances

Efficiency Calculation Example

• For a transformer supplying 190,000 W out of 200,000 W in: $ext{Efficiency} = \frac{ ext{Power out}}{ ext{Power in}} = \frac{190,000W}{200,000W} = 0.95$
  • Percentage Efficiency = ext{Efficiency} imes 100 = 0.95 imes 100 = 95 ext{%}
  • Conclusion: The transformer is efficient, wasting only 5% of the energy supplied to it.