Name of Force DefinitionExamples Gravity  Gravity is a force that attracts bodies of matter toward each other. It is a force that is everywhere there is matter  The size of the force depends on two factors: mass and distance -Force of attraction increases as mass increases -Force of attraction increases as distance decreases  Keeps the planets in orbit around the sun, moon in orbit around the earth  Holds us to the earth's surface. Weight is a measure of the force of gravity on your mass  Is responsible for the tides.  Causes acceleration of a falling object  Responsible for air and water pressure (weight of air and water!)

Name of Force DefinitionExamples Surface Tension  Liquid molecules are attracted to each other (some more than others!)  Attraction between molecules causes a “membrane” to form on the surface of liquids  Allows small insects to walk on water  Mosquitoes “attach” eggs to surface of water  Soap, kerosene, can “break” the surface tension  Blowing bubbles – stretching surface tension

Magnetic  An invisible force felt within the space around a magnet.  This space, called the magnetic field, can either attract (pull) or repel (push away) other magnets and some types of metal.  All magnets have two poles. These poles are opposites and are called the north and south poles.  Opposite poles attract, while like poles, repel.  Compasses work because of Earth’s magnetic field  Iron and Nickel can be magnetized - Other metals cannot  Magnets can be made with electricity.

Electrical  A force between two charged particles  Opposite charges attract, while like charges repel.  The size of the force depends on two factors: size of charge and distance of objects -Force of attraction/repulsion increases as the size of the charge increases -Force of attraction/repulsion increases as distance decreases  Static Electricity caused by touching or rubbing of two surfaces which causes buildup of charges  Walking across carpet – you gain electrons which are released when you touch a doorknob (attracted because it is more +)!

Turning Force causes an object in uniform circular motion to move toward the center of the circular path.  a car making a turn  the movement of a roller coaster  When you are riding in a car and the car accelerates, your body tends to move backward against the seat. Likewise, if the car stops suddenly, your body tends to move forward, in the direction of the dashboard dashboard

Buoyant Force (Upthrust)  Force equal to the weight of the fluid (liquid or gas!) that is displaced by the object.  Determined by an object’s DENSITY (mass ÷ volume!)  An object will float if Density of Object < Density of Fluid  Equal to the weight of the fluid (liquid or gas!) that is displaced by the object  Explains why ships don’t sink  Why we only see about 10% of icebergs (“tip of the iceburg”)

Friction  A force that acts in a direction opposite to the motion of a moving object.  Friction will cause a moving object to slow down and finally stop  Dependent on two factors -How hard surfaces are pushed together -The materials of which the surfaces are made  Sliding friction – when solid objects slide over one another  Rolling Friction – produced by wheels, ball bearings, etc  Fluid (liquid or gas!) Friction – when an object moves through a fluid  Lubricants reduce friction

Friction is a force that resists motion. It involves objects that are in contact with each other.