Physics

• The SI unit of energy is the joule (J).
• Work done by a force on an object equals the change in kinetic energy of the object plus any other changes in energy.
• Kinetic energy is the energy an object has due to its motion, while potential energy is stored energy that comes from position or shape.
• Force is the push or pull that causes an object's motion or acceleration.
• Kinetic energy is the energy an object has due to its motion, while potential energy is stored energy that can do work when released.
• Newton's three laws of motion describe the relationship between forces and the motion of objects.
• Energy can be transferred from one place to another or transformed into different forms.
• Inertia is the resistance of an object to changes in its motion.
• The third law of motion states that for every action, there is an equal and opposite reaction.
• The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
• Conduction:

  • Heat conduction occurs through contact
  • Heat flows from an object at high temperature to an object at low temperature
  • Materials that conduct heat well are known as conductors (e.g. metals like copper and diamond)
  • Materials that resist the flow of heat are known as insulators (e.g. wood, fiberglass, air)
  • Thermal conductivity values:
  • Copper: 380 joules per second per meter per celsius
  • Water: 0.56
  • Wood: 0.10
  • Fiberglass: 0.048
  • Air: 0.023 (good insulator if still, but can carry heat if moving)
• • Example of conduction: holding a hot pan with a wooden handle to avoid burning
• Convection:

  • Heat transfer by the movement of a fluid (liquid or gas)
  • Warm fluid rises, cool fluid descends
  • Illustration with heated water in a beaker
  • Warm air rises because it's less dense than cold air
  • Cold air sinks because it's denser
  • Example of hot ground causing warm air to rise
• Radiation:

  • Heat transfer through empty space by electromagnetic waves
  • Example with the sun heating the earth
  • Objects emit radiation as temperature increases
  • Example with iron metal emitting infrared waves and visible light at high temperatures
  • Materials react differently to radiation:
  • White objects reflect radiation
  • Black objects absorb radiation efficiently
  • Example with wearing light-colored clothing in the sun
• Energy can be transferred between objects or stored within them, but it cannot be created or destroyed.
• When work is done on an object, its internal energy changes.
• Internal energy is the total kinetic and potential energy of all particles in an object.
• Work done = energy transferred + change in internal energy
• Work done is calculated using the formula W = Fd cosθ, where F is the component of the force along the line of movement, d is the distance moved, and θ is the angle between the force and the line of movement.
• An example of a scalar quantity is speed, which only has magnitude but not direction.
• Average power = total work done / time taken