Forces and Energy

• Rubbing a balloon on a wool sweater creates electric charge on the balloon's surface, increasing its electrostatic potential energy
• The charged surface of the balloon exerts an electrostatic force, attracting your hair towards it
• Charged objects exert electrostatic forces on other objects, even if those objects aren't charged themselves
• Objects can have charges in one of two ways:

  • An object with more protons than electrons is positively charged
  • An object with more electrons than protons is negatively charged
• Two similarly charged objects require work to bring them together, increasing the potential energy of both objects
• The electrostatic force between two charged objects follows Newton’s third law, stating that for every action, there is an equal opposite reaction
• Newton's law of universal gravitation describes how the force of gravity between two objects is determined by their masses and the distance between them
• Coulomb's law quantified the force between objects with positive and negative charges, showing it decreases as the distance between charges increases
• Gravity is the force that Earth exerts on objects to pull them toward the ground
• Electricity is the movement of electrons from one place to another, flowing in a complete circle called a circuit
• Magnetic fields surround magnets and electric currents, affecting objects like compass needles
• Waves transfer energy through a medium, with examples like air and water
• Waves can be classified as mechanical waves, using matter to transfer energy, or electromagnetic waves, able to travel through a vacuum
• Three types of waves are transverse, longitudinal, and surface waves
• A transverse wave occurs when the disturbance is perpendicular to the direction of the wave
• A longitudinal wave causes the molecules in a medium to move parallel to the direction of the wave
• A surface wave is a wave in which the medium moves in a circular motion
• Key terms:

  • Equilibrium: The original position of the matter before the wave occurred
  • Crest: The highest points of a transverse wave
  • Trough: The lowest points of a transverse wave
  • Amplitude: The distance from the equilibrium position to the crest of the wave
  • Wavelength: The distance between two crests or two troughs of a wave
  • Frequency: The number of wave crests passing a point per second, measured in hertz (Hz)
• Digital recording involves sampling sound at specific intervals, converting it into binary data, ensuring higher precision and resisting deterioration
• Electromagnetic radiation includes waves like radio waves, microwaves, light, and gamma rays, with varying intensities and effects on matter
• Albert Einstein proposed that light is emitted as tiny particles called photons, observed in the photoelectric effect
• Diffraction is the bending of a wave, proving light can behave like a wave or a stream of particles
• Shorter-wavelength electromagnetic radiation, like gamma rays, X-rays, and ultraviolet rays, can cause damage to living cells
• Earth's ozone layer protects us from most of the sun's UV rays, preventing damage to living organisms