Physics Flashcards

Energy Forms:

• Kinetic Energy: Energy of movement.

• Gravitational Energy: Energy stored in objects at a height.

• Elastic Energy: Energy stored in stretched objects (e.g., a spring).

• Chemical Energy: Energy stored in chemicals (e.g., fuels, batteries, food). Released by chemical reactions.

• Heat Energy

• Light Energy

• Sound Energy

• **Electrical Energy

Energy Transformation:

• Energy is always changing from one form into another.

• Example: In a torch, chemical energy transforms into electrical energy, which then transforms into heat and light energy.

Convection:

• Liquids and gases expand when heated.

• Particles in liquids and gases move faster when hot.

• Increased particle movement causes them to take up more volume as the gaps between particles widen, while the particles themselves stay the same size.

• Hot areas become less dense, causing the liquid or gas to rise into colder areas.

Conduction:

• Thermal conductivity measures a material's ability to transfer thermal energy.

• Metals are better conductors than non-metals.

• Insulators are poor thermal energy conductors; non-metals are good insulators.

• Higher thermal conductivity means better conduction; lower thermal conductivity means better insulation.

Conductors:

• Conductors easily transmit thermal energy.

• All metals are good conductors.

• When one end of a metal rod is heated, the atoms vibrate faster.

• Increased vibration causes more frequent collisions with neighboring atoms due to close proximity in solids.

• These collisions transmit energy through the metal, increasing the rate of energy transfer.

Radiation:

• Heat transfer by waves; does not require particles.

• Energy from the sun reaches Earth via radiation.

• All objects emit radiation; hotter objects emit more radiation.

• Light-colored, shiny materials reflect radiation.

• Dark-colored, matte materials absorb and emit radiation.

Insulators:

• Poor thermal conductors used to prevent heat transfer.

• Examples: Keeping homes warm, preventing drinks from cooling or warming too quickly.

• Air is a good insulator; materials trapping pockets of air are used in winter coats and home insulation.

• Light-colored shiny materials reflect heat energy; insulated mugs/cool-bags are shiny inside to reflect heat back.

Magnets

• The Earth is a giant magnet.

• The north pole of the Earth is a geographic south pole and attracts the north pole of a compass.

Stretching and Squashing/Deformation:

• When objects are impacted, the bonds compress, and the object squashes (deformation).

• When objects are stretched, the bonds undergo tension.

• Elastic: Object returns to its original shape.

• Plastic/Inelastic: Object does not return to its original shape.

• Examples of elastic materials: Hair band, balloon.

• Examples of plastic materials: Highlighter, ruler, tissue dispenser, glasses.

• Elastic materials follow Hooke's Law: The force applied to a spring is directly proportional to the extension.

• If an elastic object is stretched too far, it reaches its elastic limit.

• Past the elastic limit, the object will no longer return to its original shape; this point is called the limit of proportionality.

Elastic Objects:

• An elastic object returns to its original size and shape when a stretching or compressing force is removed.

• Two opposite forces are required: one to cause the stretch/compression and a reaction force to hold the object in place.

• The size of the force is directly proportional to the extension or compression: Doubling the force doubles the extension/compression, halving the force halves the extension/compression.

• Force = mass \times gravitational \, field \, strength

• Extension can be investigated by applying masses to a spring. Measure original length, then measure extension with each mass added.

• Plot a graph of force against extension; a straight line through the origin indicates direct proportionality.

• The same can be done for compression by adding masses to the top of a spring.

Force and Motion:

• Forces can push, pull, or twist, transfer energy mechanically, and cause objects to speed up, slow down, change direction, or change shape.

• Speed: Distance traveled in a given time.

• Speed = \frac{distance}{time}; measured in meters per second (m/s).

Distance/Time Graphs:

• Horizontal line: Object is stationary.

• Diagonal line (upwards and to the right): Object is moving at a steady speed.

• The gradient of the line indicates speed (steeper gradient = higher speed).

• Balanced forces result in no change in motion.

• Unbalanced forces cause acceleration (speeding up, slowing down/deceleration, or changing shape).

• Unbalanced forces result in a resultant force.

• Resultant force causes acceleration.

• Resultant force size is the difference between the biggest and smallest forces, with direction being the direction of the biggest force.

• Balanced forces result in zero resultant force.

Electromagnets:

• Bar magnets are magnetic all the time, while electromagnets can be turned on and off.

• A current going through a wire causes a magnetic field around the wire.

• A solenoid (long coil of wire) has the same magnetic field as a bar magnet when current flows through it.

• Electromagnets are magnets made from current-carrying wire.

• The magnetic field can be turned on and off by controlling the current.

• Electromagnet strength can be increased by:

  • More current in the wire.

  • More turns on the solenoid per unit length.

  • A core of soft iron inside the solenoid.

• Soft iron is used because it turns on and off when the current is turned on and off.

Electric Motors:

• Made from a loop of coiled wire in a magnetic field.

• When current flows through the wire, a magnetic field forms around the wire.

• Forces on the loop of wire cause it to turn.

Energy Stores:

• Magnetic: Materials that attract or repel other magnets.

• Gravitational Potential: Objects lifted against gravity.

• Kinetic: Moving objects.

• Chemical: Energy in chemical bonds.

• Nuclear: Energy in the nucleus of atoms.

• Thermal: Heat energy.

• Elastic: Stretched or compressed objects.

• Electrical: Energy carried by electric charges.

Energy Transfers:

• Mechanically: Applying a force.

• Electrically: Moving charges.

• Heating: Applying thermal energy.

• Radiation: Energy transfer by waves.

• Wasted energy is energy transferred into unneeded forms (e.g., sound from a washing machine, heat from a light bulb).

• Wasted energy often results from friction and dissipates into the surroundings.

• Power is the rate of energy transfer.

Heat Transfer:

• Heat energy moves from areas with more heat to areas with less heat.

• Example: A bottle of water moving from a cold fridge to a warm room absorbs heat until it reaches room temperature.