Student Resources

8th Grade

Forces

• Multiple forces can act upon an object.  Forces are added together if they work in the same direction and subtracted if they work in opposite directions

• Forces are measured in units of Newtons and can be measured using a spring scale

• Balanced forces are opposite in directions and equal in magnitude.  An object remains in place

• Unbalanced forces lead to motion in a particular direction and an speed based on the magnitude of the force.

• Gravity is a force that pulls two objects with mass towards each other.  Due to the massive size of Earth, object on Earth are always pulled towards the center of Earth.

• Normal force is the force when an object rests on top of an object (i.e. - Earth's surface, table, etc.)

• Friction is a force that resists the motion of an object.  It can include solid objects, liquid substances, or gaseous substances (air resistance)

Newton's Laws of Motion:

• Law of Inertia - An object at rest stays at rest and an object in motion stays in motion at a constant velocity until acted upon by an unbalanced force.

  • • Inertia is the resistance to change velocity and it depends on mass (greater mass = greater acceleration)

    • Earth always has forces acting upon objects like friction and gravity

    • Unbalanced forces can change the direction, speed, or both of an object's motion

• Law of Acceleration - Force = Mass * Acceleration.

  • • The greater the force, the greater the acceleration (change in speed - positive or negative)

    • For a given force, the greater the mass, the lower the acceleration

• Law of Action-Reaction - Every action (force) has an equal and opposite reaction (force).

  • • This applies when two object collide (interact) together

    • Equal in magnitude and opposite in direction

Non Contact Forces

• Law of Gravitation - All matter (has mass and takes up space) attracts any other matter with a force.  The force depends on mass and distance.  The greater the mass of the two objects, the greater the force.  The closer the distance, the greater the force.

• Electrostatic Force - 

• Magnetic Force - 

Electromagnets

7th Grade

Matter

• All matter (has mass and takes up space) is made up of atoms

• All matter is classified as a pure substance (element or compound) or a mixture

• Atoms of the same type make of elements.  Atoms are symbolized by circle.

• Elements are the building blocks of our universe and are made of the same kinds of atoms.

  • • They are found on the Periodic Table of Elements (PTE)

    • Each has a chemical symbol represented by 1 or 2 letters.  The first letter is always capitalized.  For instance, H is the symbol for Hydrogen, O is the symbol for oxygen, and Na is the symbol for sodium.

• Molecules are two or more atoms chemically combined together

  • • Molecules can be atoms of different elements chemically combined together.  For example, CH4 is a molecule of 1 carbon atom chemically combined with 4 hydrogen atoms.

    • Molecules can be atoms of the same element chemically combined together.  For example, O2 is a molecule of two oxygen atoms chemically combined together.

• Compounds are two or more different atoms chemically combined together.  They are a specific type of molecule

  • • Compounds can only be separated through chemical means

    • NaCl, or table salt, is an example of a compound

• Mixtures 

  • • Mixture are different elements and/or compounds physically put together

    • Mixtures can be separated physically

    • Homogeneous mixtures have a uniform consistency (look the same) and are called solutions

    • Heterogeneous mixtures have different parts that you can see.  

• Elements, Compounds, and Mixture can be identified through different methods

  • • Chemical Formula 

      • Element have 1 capital letter (i.e. - H; Ca; Pb, C, Hg)

      • Compounds have 2 elements together in one formula (i.e. - NaCl; H2SO4; FeO3, H2O)

      • Mixtures have elements and compounds ADDED together (i.e - H2 + O2 + CO2)

    • Molecular Drawings

      • Elements have all the same atoms

      • Compound have two different atoms chemically combined (touching) and they all look the same

      • Mixtures have different elements and or compounds.  They do not look the same

Properties

• Physical properties/changes

  • Can be observed or measured without changing the identify of the substance

  • Physical change: the item changes appearance, but not what it is

  • Examples include color, density, hardness, size, shape, volume, melting point and boiling point, luster, malleability.  

  • Physical changes can be reversed or separated

  • Evidence of a physical change:

    • • Change in phase (solid, liquid, gas)

      • Change in shape or size 

      • Expected change in color

      • Dissolving

• Chemical properties

  • Describes the ability of a substance to undergo a chemical change or reaction

  • Chemical change: when the the atoms in substance(s) rearrange and create a new substance

  • Examples include color, density, hardness, size, shape, volume, melting point and boiling point, luster, malleability.  

  • Chemical changes cannot be reversed without another chemical change

  • Evidence of a chemical change:

    • • Formation of a gas

      • Formation of a precipitate (when 2 liquids form a solid)

      • Change in color (unexpected)

      • Change in temperature (unexpected)

      • Change in odor

      • Emitting of energy (light, sound)

Chemical Equations

• All chemical changes are represented by a chemical equation

• The reactant(s) (or ingredients) are shown on the left side of the equation and may include one or multiple compounds and/or elements

• The arrow shown in the middle means a chemical reaction occurred and also means "yields" or makes

• The product(s) are shown on the right side of the arrow and may include one or multiple compounds and/or elements

• A coefficient (the number in front of a molecule) indicates the number of molecules.  If no coefficient is present it is assumed as a '1'

• A subscript is present to the lower right of each element.  It tells the number of atoms of that element that is in one molecule of the substance.  If no subscript is present it is assumed as a '1'

• To calculate the number of atoms in a chemical formula, you multiply the coefficient by the subscript for each element in the formula.

Law of Conservation of Mass

• Mass (matter or atoms) is neither created nor destroyed, it can only be rearranged to create new substances

  • Atoms in a chemical reaction must be the same on both sides of a chemical equation for each element

  • Mass of the reactant(s) will equal the mass of the product(s) in a chemical reaction

• We are a closed system on Earth, which means we have a limited amount of atoms and just have chemical reactions that create new substances