Science 3rd Periodical

• Friction opposes motion. It can be static friction or kinetic friction.


  Gravitational force is a downward force that acts on all objects. It makes objects fall towards the ground.
• Friction produces heat.


  Friction affects motion.
• Static electricity is formed when two objects are rubbed together causing the electrons to move from one object to another.


  Friction may be increased by increasing the roughness of the surface.

  Friction may be decreased by making the surface smooth.
• How can you increase friction?

  By increasing the roughness of the surface.
• Static friction is present when an object is at rest.


  Kinetic friction is present on moving objects.
• Kinetic friction can be sliding, rolling, or air friction. 


  Sliding friction acts on dry, solid objects sliding on a surface.

  Rolling friction slows down the motion of the wheels on the solid surface.

  Air friction acts on an object that is falling or moving through air.
• Gravitational force or gravity is the only downward force that acts on every object. It pulls objects toward the center of Earth.


  Earth has a stronger gravitational pull than the moon, thus, an object weighs more on earth than on the moon.
• Weight is a measure of the pull of gravity on an object, weight changes from place to place.


  Mass, which is the amount of matter in an object.
• Energy is the ability to do work or any activity that requires actions.


  Energy exists in different forms such as mechanical energy, sound energy, heat or thermal energy，radiant energy, electrical energy, chemical energy, and nuclear energy.
• Mechanical energy is the energy that an object has due to its position or motion.

  Potential energy is the stored energy possessed by objects that are at rest.

  Kinetic energy is the energy possessed by objects that are moving.


  Sound energy is the form of energy possessed by sound waves. It is produced by vibrating particles.

  Thermal energy is the energy possessed by an object due to the movement of particles within it. Thermal energy is released in the form of heat.
• Light energy is a form of radiant energy that is visible to the human eyes.

  Electrical energy is the most commonly used form of energy. Electrical energy results from the flow of electric charge. 


  Chemical energy is present in food.

  Nuclear energy is stored in the nucleus of an atom and is released during nuclear reactions.
• Simple machines are machines that can be found inside your house, school, or even in every industrial place. 


  They are considered as basic machines that aid humans with their works and activities.

  When two or more simple machines are combined, complex or compound machines are formed.
• Simple machines


  • Inclined plane
  • Lever
  • Pulley
  • Screw
  • Wedge
  • Wheel and axle
• Fulcrum


  The pivot point of a lever
• Lever


  A long rigid bar that rotates around a fulcrum
• Inclined plane


  A simple machine that has one end higher than the other and is used for moving heavy objects
• First class levers


  • Fulcrum in the center
• Second class levers


  • Fulcrum at one end of the machine, load force between the fulcrum and the location where effort is applied
• Third class levers


  • Effort force applied in between the fulcrum and the load force
• Screw: can be viewed as a thin inclined plane wrapped around a cylinder. Its main function is to fasten wood by rotating it using a screwdriver. It can hold things together. 


  Wedge: can be viewed as a moving inclined plane used to cut objects. Its main function is to separate objects.
• Block and tackle pulley


  Consists of two blocks with one or more pulleys
• Single fixed pulley


  Commonly used for flag poles. Changes the direction of the force necessary to do work
• Pulley


  Version of the wheel and axle combined with a rope, chain, or some other cord to allow movements either upward and downward or back and forth
• Wheel and axle


  A wheel attached to an axle
• Pulley


  Simple machine used to redirect force
• Axle


  Rod or pole found at the center of the wheel, which allows the wheel to rotate
• Types of pulleys

  • Single fixed pulley
  • Single movable pulley
  • Block and tackle pulley
• Single movable pulley


  Pulley that moves with the load