8th Grade Science Final Exam Study Guide Flashcards

Forces

  • Balanced Forces:

    • Do not cause a change in motion.
    • Equal in size and opposite in direction.
    • Net force is 0 N.
    • Examples:
      • Wrestling someone as strong as you.
      • Tug of war with equally strong teams.

  • Unbalanced Forces:

    • Always cause a change in motion.
    • One force is larger than the other.
    • Net force is greater than 0 N.
    • Forces are not equal and opposite.
    • Examples:
      • Arm wrestling match with you and a bodybuilder.
      • Tug of war with your friends vs. an Olympic weightlifting team.

Speed

  • Definition:

    • Speed is the distance traveled divided by the time taken to travel that distance.

  • Speed-Time Graphs:

    • Object at Rest: The line rests on the x-axis.
    • Constant Speed: The speed isn’t changing; represented by a straight line.
    • Increasing Speed (Acceleration): The line on the graph is curving upwards.
    • Faster Acceleration: Represented by a steeper line.
    • Slowing Down: A downward sloping line.

Laws of Motion

  • 1st Law (Law of Inertia):

    • An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
    • Inertia: The tendency of an object to resist its motion.
      • The greater the mass, the higher the inertia.

  • 2nd Law:

    • Relationship between force, mass, and acceleration.
    • A force upon an object causes it to accelerate.
    • force = mass \times acceleration

  • 3rd Law:

    • For every action (force) in nature, there is an equal and opposite reaction.
    • Forces act in equal but opposite pairs (action/reaction).

Gravity

  • Gravitational force decreases as distance increases (inverse relationship).

    • The closer the objects, the greater the gravitational force.

  • Gravitational force increases as mass increases (direct relationship).

  • Acceleration of gravity is approximately 9.8 m/s^2.

  • Mass:

    • How much matter an object has.
    • Always constant.

  • Weight:

    • Force exerted on a mass by gravity.
    • Not constant; can change depending on location (due to varying gravitational forces).

Magnetism/Magnetic Forces

  • Magnetism:
    • Force exerted by magnets when they attract or repel each other.
  • Magnetism increases as distance decreases.

Electricity

  • Transferring Electrons:

    • If electrons leave a surface, the surface becomes positively charged (more protons than electrons).
    • If electrons are added to a surface, the surface becomes negatively charged (more electrons than protons).

  • Electric Fields:

    • Strength increases as you get closer to the charge.
    • The more charges present, the stronger the force.

Heat Energy

  • Conduction:
    • Direct contact.
  • Convection:
    • Currents in air or water moving in a circular pattern.
  • Radiation:
    • Electromagnetic waves.

Potential and Kinetic Energy

  • Potential Energy:

    • Energy stored in an object because of its position.
    • The higher the object, the higher the potential energy.
    • The more mass an object has, the more potential energy it has.

  • Kinetic Energy:

    • Energy an object has due to its motion.
    • No motion, no kinetic energy.
    • Increases as an object moves faster.
    • Increases as mass increases.

  • Conservation of Energy:

    • The total amount of energy remains constant.
    • Decrease in kinetic energy = increase in potential energy.
    • Decrease in potential energy = increase in kinetic energy. Example: A falling object converts potential energy to kinetic energy as it falls but the total energy of the object is constant.