Grade 8 Science

• Newton's first law of motion

  The law of inertia, which explains how an object responds to changes in motion
• Force


  Any push or pull that causes changes in the motion of an object
• Types of force


  • Contact force
  • Non-contact force
• Contact force


  Present when two or more surfaces or media touch and interact
• Friction


  A specific type of contact force, the object's resistance to motion
• Non-contact force


  Constantly present in nature and does not need human intervention to arise
• Non-contact force


  • The sun and planets exerting a gravitational pull on each other despite their large spatial separation
• Aspects of motion


  • Speed
  • Velocity
  • Acceleration
• Speed


  The length of distance traveled in a certain amount of time
• Velocity


  The rate of change of displacement of an object
• Acceleration


  The rate of change of velocity of an object
• Newton's first law of motion


  The response of an object to changes in motion
• Parts of Newton's first law of motion

  • An object at rest will remain at rest unless acted on by an unbalanced force
  • An object in motion continues to move with the same velocity unless acted on by an imbalanced force
• Inertia


  The property that resists the changes in an object, independent from external force and mass-dependent
• An object at rest will remain at rest, and an object in motion will remain in motion, unless acted on by an unbalanced force
• Newton's second law of motion

  The acceleration of an object is directly proportional to the net force on it and inversely proportional to its mass
• Newton's law of acceleration

  Force acting on an object = Mass of object x Acceleration of object
• Greater mass of object


  Greater force needed to accelerate the object
• Force = Mass x Acceleration
• Acceleration = Force / Mass
• Mass = Force / Acceleration
• Weight


  Force due to gravity = Mass x Acceleration due to gravity (9.8 m/s^2)
• Newton is the unit of force, equal to 1 kg·m/s^2
• Action and reaction forces

  The two forces resulting from the interaction between objects
• Newton's third law of motion (law of interaction)


  For every action there is an equal and opposite reaction
• In every interaction, there is a pair of forces acting on the two interacting objects, with the size of the forces on the first object equaling the size of the force on the second object, and the direction of the force on the first object being opposite to the direction of the force on the second object
• When a body exerts a force on another, an equal amount of force is always exerted back on it
• Roller coaster


  Does not have an engine, relies on gravity to take it to the end of the track
• Gravity


  The force that pulls things to the ground
• Energy


  The ability to do work, has the same unit as work which is joule
• Energy


  • Changes from potential to kinetic energy and back again many times over the course of a ride
• Potential energy


  Stored energy due to the position of an object
• Types of potential energy

  • Chemical potential energy
  • Physical potential energy (gravitational potential energy)
• Chemical potential energy


  Found in substances that store energy at a sub-microscopic level, has the readiness to undergo a chemical change
• Examples of chemical potential energy

  • Food we eat
  • Batteries we use for gadgets
  • Gasoline that runs cars
• Physical potential energy (gravitational potential energy)


  Due to the work required to elevate objects against earth's gravitational pull, the energy of position
• Potential energy depends only on the initial and final position, not the path
• Gravity


  The force the earth exerts on all objects on its surface, always directed downward
• Gaining and losing potential energy

  1. Object gains energy when raised from the ground

  2. Object loses energy when made to fall
• Kinetic energy


  The energy of a moving object