GRAVITY, MAGNETISM, AND ELECTRICITY UNIT FORCES AND INTERACTIONS

GRAVITY

A plane falls from the sky, an apple falls from the tree these events take place because gravity. Gravity is a force that pulls objects toward each other. Issac Newton concluded that a force acts to pull objects straight toward the center of the earth.

UNIVERSAL GRAVITATION Newton realized that gravity acts everywhere in the universe, not just on Earth. It is the force that keeps all the planets in our solar system orbiting around the sun.

UNIVERSAL GRAVITATION The law of universal gravitation state that the force of gravity acts between all objects in the universe. This means that any two objects in the universe, without exception attract each other.

FACTORS AFFECTING GRAVITY Two factors affect the gravitational attraction between objects: mass and distance Mass is a measure of the amount of matter in an object.  Mass is measured in kilograms

FACTORS AFFECTING GRAVITY The more mass an object has, the greater its gravitational force. In addition to mass, gravitational force depends on the distance between the objects. The farther apart two objects are, the lesser the gravitational force.

WEIGHT AND MASS Mass is the measure of the amount of matter in an object Weight is the amount of gravitational force exerted on an object DON’T GET THESE TWO CONFUSED!!!!!!!!!!!

WEIGHT AND MASS The force of gravity on a person or object at the surface of a planet is known as weight Weight varies with the strength of the gravitational force but mass does not. Astronaut in Space Weight on Moon270 N Weight on Earth1,617 N Mass on Moon165 kg Mass on Earth165 kg

GRAVITY AND MOTION When you hold a book, you exert a force that balances the force of gravity. When you let go of the book, gravity becomes an unbalanced force and the book falls

FREE FALL When the only force acting on an object is gravity, the object is said to be in free fall.  Objects in free fall is accelerating In free fall the forces of gravity is an unbalanced force, which causes an object to accelerate.

FREE FALL

Near the surface of the earth the acceleration due to gravity is 9.8 m/s² This means that for every second an object is falling, its velocity increases by 9.8 m/s In the absence of air, two objects with different masses fall at exactly the same rate.

AIR RESISTANCE Theoretically, all objects are supposed to fall at the same rate but we know that this is not always the case. Objects falling through air experiences a type of fluid friction called air resistance

Friction is the direct opposite to motion, so air resistance is an upward force exerted on falling objects Not all objects have the same air resistance Objects with more surface area has more air resistance

AIR RESISTANCE Air resistance increases with velocity, or speed in a given direction. As the object falling speeds up, the force of air resistance increases At one point, an object falling will fall fast enough that the upward force of air resistance becomes equal to the downward force of gravity on the object.

AIR RESISTANCE The object continues to fall, but its velocity remains constant. The greatest velocity a falling object reaches is called its terminal velocity  Force of air resistance = weight of the object

INTRODUCTION TO ELECTRICITY

ELECTRICITY e - movement negatively charged area  positively charged area The movement of electrons from one place to another

ATOMS AND CHARGE All matter is composed of small particles called atoms Atoms are composed of even smaller particles called protons, neutrons, and electrons Electrons = negative charge Protons = positive charge Neutrons = no charge

CHARGES CAN EXERT FORCES A charge is a physical property that describes how charged objects interact with one another. A charge exerts a force----a push or a pull There are two types of charges  Positive  Negative Forces depend on weather the forces are the same type or opposite

CHARGES CAN EXERT FORCES The law of electric charges states that like charges repel and opposite charges attract

THE ELECTRIC FORCE AND THE ELECTRIC FIELD The force between charged objects is an electric force The strength of the electric force is determined by two factors:  Size of the charges –greater the charge the greater the force  Distance –closer together the charges are the greater the force

THE ELECTRIC FORCE AND THE ELECTRIC FIELD The electric force exists because charged particles have electric fields around them. An electric field is a region around a charged particle that can exert a force on another charged particle.

ELECTRIC FIELDS Electrical field two charges are separated vectors (lines of force) point towards negative charges and away from positive charges strength of field (magnitude)= distance between two charges closer particles = stronger field A force field that fills the space around electrical charges

STATIC ELECTRICITY e - displaced & builds charge (not moving through a conductor) Eventually electrons “jump” to a positively charged object Examples Plastic sheet & hair Walking on carpet & Touching a metal doorknob Electrons are displaced WITHOUT moving through a conductor

MAGNETS AND MAGNETISM

MAGNETS Elements that can be magnetic 1.Fe: Iron soft iron loses magnetism easily 2.Co: Cobalt used to harden tools 3.Ni: Nickel used to make jewelry Other magnets: 1.Compass 2.Earth Materials whose atoms can be aligned

PROPERTIES OF MAGNETS Any material that attracts iron, nickel, or cobalt is called a magnet. All magnets have the following properties:  Two poles  Create a magnetic field  Exert force

The parts of the magnet where the magnetic effects are the strongest are called the poles If you attach a string to a magnet and let it hang there is one end that will always point itself to the north.  The part of the magnet that orients itself north is called the north pole of the magnet  The part of the magnet that orients itself south is called the south pole of the magnet MAGNETIC POLES

The force of repulsion or attraction between the poles of magnets is called the magnetic force. The magnetic force between magnets depend on how the magnets line up MAGNETIC FORCES

A magnetic field exists in the region around a magnet in which magnetic forces can act. MAGNETIC FIELDS

Magnetic field lines 1.Leaves north pole & enters south pole 2.Lines closer together = stronger field NOTICE 1.Strongest at the poles 2.Field lines start at the NORTH pole and travel towards the SOUTH pole An area where the force exists; area where force is felt

WHAT MAKES A MATERIAL MAGNETIC? ATOMS AND DOMAINS All matter is made of atoms with moving electrons. Moving electrons create a magnetic field. In metal objects atoms are grouped together in tiny regions called domains The arrangement of the domains in an object determines whether the object is magnetic

EARTH AS A MAGNET Recall that if a magnet is allowed to hang freely it will point to the north. In fact, every time you use a compass you take advantage of this property, because a compass contains a freely rotating magnet. The real question is why do magnets point north?

In 1600 an English scientist named William Gilbert suggested that magnets point to the north because Earth itself is one giant magnet. Each does behave as if it has a bar magnet running through its core. ONE GIANT MAGNET

Why does the needle of a compass point north?  The magnetic pole of Earth that is closest to the geographic north pole is actually the magnetic south pole. NORTH IS SOUTH

THE CORE OF THE MATTER Scientists think that the Earth’s magnetic field is produced by the movement of electrons in the Earth’s core. The inner core is a solid iron and nickel The outer core is liquid metal because there is less pressure. As earth rotates the liquid in the core flows and causes electric charges to move creating a magnetic field.

A MAGNETIC LIGHT SHOW One of the most spectacular effects caused by the Earth’s magnetic fields is a curtain of light called and aurora. An aurora is formed when charged particles from the sun interact gases in the atmosphere. When the charged particles hit the gases they emit light. Earth’s magnetic fields at like a barrier so you really only see an aurora near the north and the south pole The lights seen near the northern magnetic pole is called aurora borealis or the northern lights

MAGNETISM FROM ELECTRICITY

THE DISCOVERY OF ELECTROMAGNETISM In 1820 Danish scientist Hans Christian Oersted discovered the relationship between electricity and magnetism. Oersted concluded that an electric current produces a magnetic field  The direction of the magnetic field depends on the direction of the current. Electromagnetism is the interaction between electricity and magnetism

ELECTRICITY  MAGNETISM How can you tell? Compass needle moves when near electrical current - creating an magnetic field Electric currents cause magnetism

ELECTROMAGNET Electromagnetism a moving charge (electricity) produces a magnetic field More coils of wire= more current = stronger magnet Bigger battery = stronger magnet A magnet with a field produced by an electric current

ELECTROMAGNETIC INDUCTION 1831 – Michael Faraday (England) and Joseph Henry (US) independently discovered that electric current could be produced by moving a magnet in and out of a coil wire

ELECTROMAGNETIC INDUCTION preview.weml

MAGNETISM  ELECTRICITY How can you tell? Electromagnetic induction moving a magnet in and out of a coiled wire created an electrical current without a battery Moving magnet can generate electricity

Both can cause each other Likes repel Opposites attract SUMMARY OF E & M ELECTRICITY Can be + or - Can flow (current) Can jump (static) E = Electricity and M = Magnetism are related!! MAGNETISM ► Can NOT have only 1 pole ► Can be Normal (N) or Reversed (S) pole ► Can move through field ► Causes sun spots, flares, CME