Energy flashcards

Physics Notes

1. Energy

• Definition: The ability of an object to do work.

  • Unit: Joules

• Types of Energy:

  • Mechanical: Energy of Movement and Position.

  • Chemical: Energy stored in chemical bonds of molecules.

  • Thermal: Heat energy.

  • Nuclear: Energy produced from the splitting of atoms.

  • Radiant: Energy in the form of electromagnetic waves.

  • Electric: Energy traveling as the flow of charged particles (electrons).

2. Work

• Definition: Work is done when a task produces a change in energy.

  • Factors that affect work: Force and Distance.

  • Formula: W = Fd ( \text{Note: work requires a distance!} )

  • Example problems:

    • To lift an object 2m high using 5N of force: 10 Joules.

    • Pushing a stationary wall with a force of 1000 N: 0 Joules (no movement).

3. Power

• Definition: How much work is performed over a certain amount of time.

  • Formula: P = W/T

  • Unit: Watts (W).

  • Horsepower:

    • 1 hp = 746 Watts

    • 1 horsepower = the output of a farm horse.

  • Common items converted to horsepower:

    • Coffee maker: 0.75 hp

    • Blender: 1.5 hp

    • Lawn mower: 5-6 hp

    • Corvette: 400+ hp

  • Example problem:

    • Superman, at 90kg, jumps a 40m building: 35,280 Joules of work in 3s gives a power output of 71,760 Watts.

4. Work Dependence

• The amount of work done by an object does not depend on the path taken.

  • Work on an object gives it the opportunity to do work (e.g., winding a toy).

5. Mechanical Energy

• Definition: Energy of movement and position.

  • Potential Energy:

    • Energy of Position.

    • Gravitational Potential Energy: due to elevated positions.

      • Formula: PE = mgh

  • Kinetic Energy:

    • Energy of Motion.

    • Formula: KE = 1/2mv². Note: Velocity is squared.

    • Energy Conservation:

      • Energy is constantly transforming but never disappears.

      • Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.

      • PE = KE in a system.

      • On a roller coaster:

        • Greatest PE at A, lowest at B.

        • Greatest KE at B, lowest at A.

Problems:

• Jill: Velocity 5m/s, mass 60kg: Kinetic Energy = 752J.

• Bob: Mass 70kg, height 13m: Potential Energy = 8,918J.

6. Hooke’s Law

• Definition: The amount of force applied to a spring is proportional to the amount it’s stretched or compressed.

  • Formula: F = kx.

Momentum

• Definition: Momentum is a measure of the quantity of motion an object possesses.

• Formula: [ P = m \times v ]

  • Where:

    • P is momentum (symbolized as (P))

    • m is the mass of the object

    • v is the velocity of the object

• Units: Momentum is expressed in kg·m/s.

Standard units and Letter abbreviation: