Review Test Notes: Energy and Work Done
Energy and Work Done: Review Test Notes
Types of Energy
a. Kinetic Energy: The energy possessed by moving objects.
b. Electrical Energy: Energy present when an electrical current is flowing.
c. Gravitational Potential Energy: Energy stored by an object due to its position within a gravitational field.
d. Light Energy (Luminous Energy): Energy emitted by luminous objects.
e. Elastic Potential Energy: The potential energy stored in a stretched rubber band.
f. Sound Energy: Energy transmitted by noisy objects.
g. Thermal Energy: Hotter objects possess more thermal energy compared to cooler objects.
Energy Conversions
a. Burning Match: Chemical energy transforms into heat and light energy.
b. Electric Light Bulb: Electrical energy converts into light and heat energy.
c. Windmill Connected to a Generator: Kinetic energy (wind) converts into mechanical energy (windmill) and then into electrical energy (generator).
d. Loudspeaker at a Pop Concert: Electrical energy transforms into sound energy.
e. Solar Cell on a Student’s Calculator: Light energy (solar) converts into electrical energy.
f. Sledge Sliding Down a Slope: Gravitational potential energy converts into kinetic energy and thermal energy (due to friction).
g. Battery Powered Radio: Chemical energy (battery) converts into electrical energy, then into sound energy.
Principle of Conservation of Energy
The principle of conservation of energy states that energy can neither be created nor destroyed, but is only converted from one form to another.
Energy Transformation of a Falling Can of Paint
When a can of paint falls and comes to rest, all of the kinetic energy is transferred into heat energy (due to the impact) and sound energy.
Energy Resources
a. Energy resources that do not rely on photosynthesis: Geothermal and Nuclear.
b. Example of biomass: Wood.
c. How Solar Cells Use Solar Energy: Solar cells convert light energy from the sun directly into electrical energy through the photovoltaic effect.
Electricity-Generating Power Stations
a. Energy in Fuel Supply: Chemical energy.
b. Energy in the Boiler: Thermal energy (heat).
c. Energy Transfer in the Generator: Mechanical energy → Electrical energy
Non-Renewable Energy
What does non-renewable mean? An energy source that cannot be readily replaced by natural means on a level equal to its consumption.
Fossil Fuels as Non-Renewable Resources
Fossil fuels are considered non-renewable because they take millions of years to form. The rate at which we use them far exceeds the rate at which they are created.
Reducing Fossil Fuel Usage
Use renewable energy sources like solar, wind, and hydro power.
Improve energy efficiency by using energy-saving appliances, better insulation, and more efficient transportation methods.
Renewable Energy Resources
Wind, biomass and waves are examples of energy resources that make use of energy emitted by the Sun. We know that these energy resources won’t run out because the sun's energy is virtually endless on a human timescale. They are continuously replenished.
Definition of Energy
Energy is the ability to do work.
Conditions for Work Done
A force must be applied to an object.
The object must move in the direction of the applied force.
Advantages and Disadvantages of Energy Production Methods
Energy Production Method | Advantage | Disadvantage |
|---|---|---|
Fossil fuels | High energy output; reliable. | Contributes to greenhouse gas emissions; non-renewable. |
Biofuels | Renewable; can be carbon neutral. | Requires land use; may increase food prices; lower energy output than fossil fuels. |
Geothermal energy | Renewable; consistent energy supply. | Geographically limited; potential for environmental impacts (e.g., release of gases). |
Hydroelectric energy | Renewable; reliable; can control water flow (e.g. flood control). | Can disrupt ecosystems; expensive to build; dependent on rainfall. |
Solar energy | Renewable; clean energy. | Intermittent (dependent on weather and time of day); requires large areas; manufacturing of solar panels can be energy intensive. |
Wind energy | Renewable; clean energy. | Intermittent (dependent on wind); noisy; can be a threat to birds and bats; visual impact. |
Formula for Calculating Work Done
The mathematical formula for calculating work done is: W = F
delta x where:
W = Work done (in Joules)
F = Force applied (in Newtons)
\delta x = Distance over which the force is applied (in meters)
Examples of Work Done
The following examples involve work being done:
a. A grocery bag as you lift it up
b. A crane moving dirt
c. A crate as you push it along the floor
Work Done by Lifting a Dragon
Given:
F = 30 N
\delta x = 2 m
W = F \delta x = (30 N)(2 m) = 60 J
The boy did 60 Joules of work on the dragon.
Distance Beam Lifted by Crane
Given:
W = 13,500 J
F = 5200 N
W = F \delta x \implies \delta x = \frac{W}{F} = \frac{13,500 J}{5200 N} \approx 2.6 m
The beam can be lifted approximately 2.6 meters.