10.1_The_Basic_Energy_Model

Section 10.1 The Basic Energy Model

• Introduction to the concept of energy.

Total Energy

• Every system in nature has a quantity called total energy (E).

Forms of Energy

Key Types of Energy:

• Kinetic Energy (K):

  • Energy associated with motion.

• Gravitational Potential Energy (Ug):

  • Energy stored based on an object's height above the ground.

• Elastic or Spring Potential Energy (Us):

  • Energy stored when an elastic object, like a spring, is stretched or compressed.

• Thermal Energy (Eth):

  • The sum of kinetic and potential energies of molecules within an object.

• Chemical Energy (Echem):

  • Energy stored in the bonds connecting molecules.

• Nuclear Energy (Enuclear):

  • Energy stored within the atomic nucleus.

Energy Transformations

• Energy can change from one form to another within a system.

Examples of Energy Transformations

• A weightlifter transforms chemical energy from her body into gravitational potential energy of the barbell.

• Elastic potential energy of a springboard is converted into kinetic energy.

• As a diver rises, kinetic energy converts into gravitational potential energy.

QuickCheck 10.1

• Scenario: A child on a swing at its highest point.

• Question: What energy transformation occurs as he swings down?

• Answer Options:

  • A. K → Ug

  • B. Ug → K

  • C. Eth → K

  • D. Ug → Eth

  • E. K → Eth

• Correct Answer: B. Ug → K

QuickCheck 10.2

• Scenario: A skier gliding down a slope at constant speed.

• Question: What energy transformation occurs?

• Answer Options:

  • A. K → Ug

  • B. Ug → K

  • C. Eth → K

  • D. Ug → Eth

  • E. K → Eth

• Correct Answer: B. Ug → K

Energy Transfers and Work

• Energy transfer occurs through work and heat.

Definitions:

• Work:

  • Mechanical transfer of energy via pushing or pulling on a system.

• Heat:

  • Non-mechanical transfer of energy based on temperature differences.

Energy Transfers in Action

• The athlete applies work on a shot, increasing its kinetic energy (K).

• Work done on a match gives it thermal energy (Eth).

• Work done on a slingshot provides it with elastic potential energy (Us).

QuickCheck 10.3

• Scenario: A tow rope pulls a skier up a slope at constant speed.

• Question: What energy transfer occurs?

• Answer Options:

  • A. W → Ug

  • B. W → K

  • C. W → Eth

  • D. Both A and B

  • E. Both A and C

• Correct Answer: A. W → Ug

The Work-Energy Equation

• Work is energy transferred into or out of a system.

• The total energy change in a system is equal to the work done on it.

• Work can either increase or decrease a system's energy.

• An isolated system does not have energy transferred in or out.

QuickCheck 10.4

• Scenario: A crane lowering a girder at constant speed.

• Question: Consider the work done by gravity (Wg) and by the cable tension (WT).

• Answer Options:

  • A. Wg > 0 and WT > 0

  • B. Wg > 0 and WT < 0

  • C. Wg < 0 and WT > 0

  • D. Wg < 0 and WT < 0

  • E. Wg = 0 and WT = 0

• Correct Answer: C. Wg < 0 and WT > 0

QuickCheck 10.5

• Scenario: Robert pushes a box to the left at constant speed.

• Question: What kind of work does Robert do on the box?

• Answer Options:

  • A. positive

  • B. negative

  • C. zero

• Correct Answer: A. positive

The Law of Conservation of Energy

• The total energy of an isolated system is conserved and remains constant.