unit 4: Energy
Overview
Energy is the stuff we need to do stuff. Energy can come in all types of forms (Thermal, Kinetic, Electrical, Light, Potential, & Food Energy). When energy is transferred from object to object in a system, Work is being done. In a closed system, the total amount of energy at the beginning of an action must equal the total amount of energy at the end of the action.
Mechanical Energy = Potential Energy + Kinetic Energy
Gravitational Potential Energy (Eg, Ug)
Energy is the stuff we need to do stuff. Energy can come in all types of forms (Thermal, Kinetic, Electrical, Light, Potential, & Food Energy). When energy is transferred from object to object in a system, Work is being done. In a closed system, the total amount of energy at the beginning of an action must equal the total amount of energy at the end of the action.
Mechanical Energy = Potential Energy + Kinetic Energy
- Potential Energy - energy stored based on the position of an object in the system
- Kinetic Energy - energy of an object obtained in motion
Gravitational Potential Energy (Eg, Ug)
- Gravitational energy caused by the distance between the Earth and an object
- Stored elastic energy in elastic material when you stretch or compress it
- Elastic material wishes to return to its equilibrium position
- Energy stored in chemical bonds and reactions
- Food, gasoline, coal
- Energy stored in objects in motion
- Energy stored in the random motion of atoms in a system
- Can be transferred caused by friction
- Temperature/how fast particles are moving
Law of Conservation of Energy
- Initial mechanical energy = Final Mechanical Energy
- Energy is never created or destroyed
- The entire universe is the system
- No energy leaves the universe, therefore energy is only transferred
Types of Energy Transfers
- Working (W) - external push or pull on the system
- Heating (Q) - temperature different between system and surrounding, from warmer object to cooler object
- Radiating (R) - matter loses energy through radiating light, gains energy through absorbing light
Representing Energy Transfers with Bar Charts (LOL)
- Total energy at initial position + Input of Energy (+W, +Q, +R) = Total energy at final position
- Total energy at initial position - Output of Energy (-W, -Q, -R) = Total energy at final position
- Demonstrates the different types of energies
- Energy bars are not units
- Law of Conservation of Energy is demonstrated, initial energy = final energy
Work - Transfer of energy
Positive Work
|
Negative Work
|
Formula for Work
W = F • Δx
Dot Product
W = F • Δx
- F = force
- Δx = change in position
- F II = parallel force
- d = displacement
- Perpendicular forces do no work
Dot Product
- Multiple the vectors together
Power
Power
Humans vs other animals
- Rate of transfer of energy
- Transfer of energy while force is acting over certain distance
- Watt is the unit of power (1W, 1 J/s)
- Total work/ Change in time (s)
Humans vs other animals
- The average output for a human throughout a day is 97W
- Horsepower: a horse has the power of about 736 watts per second
Energy Problem Solving
Steps
1. Draw LOL Chart
2. Identify the different types of initial energy and final energy (K, Ug, Us, Uint, Uchem)
3. In a closed system, ensure that total initial energy must equal total final energy
4. In an open system, ensure the total initial energy plus the output or input of energy (W, R, Q) must equal the total final energy
5. Write the conservation of energy equation
Relating Energy/Work/Power to Forces and Motion
1. Draw LOL Chart
2. Identify the different types of initial energy and final energy (K, Ug, Us, Uint, Uchem)
3. In a closed system, ensure that total initial energy must equal total final energy
4. In an open system, ensure the total initial energy plus the output or input of energy (W, R, Q) must equal the total final energy
5. Write the conservation of energy equation
Relating Energy/Work/Power to Forces and Motion
- Initial Energy + W = Final Energy or Initial Energy - W = Final Energy
- W = Force * Δx
- P = W / Δt, P = (Force * Δx) / Δt
Connecting Representations of Motion with Representations of Forces with Representations of Energy
Force in relation to Energy
- The force diagram allows us to visualize the different types of energies
- Forces that are perpendicular do no work
- A force that is acting in opposite direction of another force does work