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 Moon
270 N
Weight on Earth
1,617 N
Mass on Moon
165 kg
Mass on Earth
165 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
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
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ELECTRICITY
The movement of electrons from one place to another
e- movement
negatively charged area 
positively charged area
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
A force field that fills the space around electrical
charges
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
STATIC ELECTRICITY
Electrons are displaced
WITHOUT moving through
a conductor
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
https://www.brainpop.com/science/motionsforcesandtime/magnetism/
MAGNETS
Materials whose atoms can be aligned
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
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
MAGNETIC POLES
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 FORCES
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 FIELDS
A magnetic field
exists in the
region around a
magnet in which
magnetic forces
can act.
MAGNETIC FIELDS
An area where the force exists; area where force is felt
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
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?
ONE GIANT MAGNET
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.
NORTH IS SOUTH
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.
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
https://www.youtube.com/watch?v=ZxyT26Lg55Q
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
Electric currents cause magnetism
How can you tell?
Compass needle moves
when near electrical current
- creating an magnetic field
ELECTROMAGNET
A magnet with a field produced by an electric current
Electromagnetism
a moving charge
(electricity) produces a
magnetic field
More coils of wire=
more current =
stronger magnet
Bigger battery =
stronger magnet
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
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MAGNETISM  ELECTRICITY
Moving magnet can generate electricity
How can you tell?
Electromagnetic induction
moving a magnet in and out of
a coiled wire created an
electrical current without a
battery
SUMMARY OF E & M
E = Electricity and M = Magnetism are related!!
ELECTRICITY
• Both can cause
each other
Can be + or -
MAGNETISM
►
Can NOT have only
1 pole
►
Can be Normal (N)
or Reversed (S) pole
►
Can move through
field
►
Causes sun spots,
flares, CME
Can flow (current)
Can jump (static)
• Likes repel
• Opposites attract