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:

Standard unit

Letter Abbreviation (in a formula)

mass

kg

m

momentum

kgm/s

P

Velocity

m/s

v

Kinetic energy

J

KE

Spring constant

N/m

K

Power

W

P

Work

J

W

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