Transcript Newton`s Laws of Motion

Newton’s Laws of Motion
• The Laws of Motion are governed by three principles
developed by one man…Sir Isaac Newton (16431727)
Law of Inertia
• Every object in motion stays in motion and
any object at rest stays at rest until acted
upon by an outside force.
• Inertia: is the term for the property of matter
that resists change in its state of motion.
– Why aren’t you falling out of your seats?
– Why is it so hard to push a car out of the mud?
– Why is it even harder to push a cruise ship off the
dock?
• Objects at rest want to stay that way!
Motion
• Motion is a change in position relative to a
frame of reference
• Speed is the distance traveled in a given
amount of time
• Speed=distance
time
Objects in motion want to stay that way!
Why is it harder to stop an 18-wheeler moving at
60 mph than a compact car moving at the same
speed? A: 18 wheeler has more mass!!!
• If no breaks were applied, would the two
vehicles move forever? NO!!!!!!!!!
• But I thought objects in motion wanted
to stay that way???
• Friction is a force opposing motion, caused by
the contact of two surfaces.
Drawing Net forces
1
• The law of inertia is most commonly
experienced when riding in cars and trucks.
• Consider the unfortunate collision of a car with
a wall.
– Upon contact with the wall, an unbalanced force acts
upon the car to abruptly decelerate it to rest.
– Any passengers in the car will also be decelerated to
rest if they are strapped to the car by seat belts.
• Being strapped tightly to the car, the
passengers share the same state of motion as
the car.
– As the car accelerates, the passengers accelerate
– As the car decelerates, the passengers decelerate
As the car maintains a constant speed, the
passengers maintain a constant speed.
But what would happen if the passengers were
not wearing the seat belt?
What motion would the passengers undergo if
they failed to use their seat belts and the car
were brought to a sudden and abrupt halt by
a collision with a wall?
1
1
• If the car were to abruptly stop and the seat
belts were not being worn, then the
passengers in motion would continue in
motion.
• Assuming a negligible amount of friction
between the passengers and the seats, the
passengers would likely be propelled from the
car and be hurled into the air.
• Once they leave the car, the passengers
become projectiles and continue in projectilelike motion.
1) From: The Car and The Wall http://www.geocities.com/Athens/Academy/9208/cci.html
Velocity
• Speed in a given direction
• Velocities in the same direction combine by adding
• Velocities in different directions combine by
subtracting
Acceleration
•
•
•
•
The change in velocity
Acceleration is measured in m/sec/sec or m/sec2
Formula is:
(final velocity - original velocity)/time
Deceleration vs. Acceleration
• A decrease in velocity is deceleration or negative
acceleration
• A distance-time graph for acceleration is always a curve
Centripetal Acceleration
• Acceleration directed toward the center of circular path
Law of Inertia
An object’s orientation
can change it’s
inertia by altering its
center of gravity!
Center of Gravity: the
average location of the
weight of an object.
While all objects exhibit the property of inertia, all
objects do not have the same inertia! Think about
it… is it easier to kick an empty can or a full can?
Inertia is affected by mass.
Mass: is the quantity of matter in an object.
**Mass is not weight!**
Weight: is a measure of an object’s gravitational
attraction to earth. Weight can change. Mass does
not!
Why is it easier to kick an empty can than a full can?
The full can had more mass and therefore, more
inertia.
In other words, the more mass an object has, the more
it will resist change in its state of motion.
Newton’s 2nd Law
(a.k.a.)
F=mxa
• The acceleration produced by a net force on an
object is directly proportional to the magnitude of the
net force, is in the same direction as the net force,
and is inversely proportional to the mass of the
object.
• So what does this mean??? The amount of force
applied to an object is equal to the mass of the object
multiplied by its acceleration due to that force:
F=mxa
• What is acceleration? How fast something speeds
up.
Gravity
• Gravity is a force of attraction between two
bodies with mass.
• Since all object have mass, all objects exert
gravity on all other objects. Even you have
your own gravity.
• So why don’t we observe our own gravity?
Because compared to the earth, our mass is
very, very small…so small that our own
gravity is too small to observe.
• More mass = More Gravity
Gravity
• Gravity is a force
applied to all objects
by the earth. No
matter what the
object, the
acceleration due to
gravity is 9.8 m/s2.
Example:
A textbook has a mass of 1 kg and a piece of paper has a mass of
0.0001kg. What is the force of gravity on each of these falling
objects?
F = ma
F= ma
Ftextbook = 1kg x 9.8 m/s2
Fpaper = 0.0001kg x 9.8m/s2
Ftextbook = 9.8 N
Fpaper = 0.00098 N
A Newton, N, is equal to a kg m/s2
Was the force of gravity on the textbook and the paper the same?
Does this mean that they should fall at the same time or not?
What was the real reason that they did not fall at the same time?
Air resistance works against the force of gravity.
Air Resistance: Friction due to air.
Because the piece of paper has more air resistance, its acceleration
due to gravity is slowed. Other forces are resisted by friction.
• Free Fall: falling free of air resistance or other
constraints.
• On earth, we do not have the luxury of experiencing free
fall, but we can experience something similar…
• Terminal Velocity: The point in movement where the
force propelling the object forward is equal to the forces
resisting the forward motion (i.e. air resistance/friction =
gravity) causing the speed of the object to be constant.
• Suppose that air resistance
could be eliminated so
neither the elephant nor the
feather would experience
any air drag during the
course of their fall.
• Which object - the elephant
or the feather - will hit the
ground first?
• Many people are surprised
by the fact that in the
absence of air resistance,
the elephant and the feather
strike the ground at the same
time.
3) From: Elephant and Feather-Air Resistance
http://www.geocities.com/Athens/Academy/9208/efff.html
• In the absence of air resistance, both
the elephant and the feather are in a
state of free-fall. That is to say, the only
force acting upon the two objects is
gravity.
• This force of gravity is what causes both
the elephant and the feather to
accelerate downwards. The force of
gravity experienced by an object is
dependent upon the mass of that object.
Why then does it hit the ground
at the same time as the feather?
3
• When figuring the acceleration of object, there are two
factors to consider - force and mass.
• The elephant experiences a much greater force (which
tends to produce large accelerations. Yet, the mass of
an object resists acceleration.
• The greater mass of the elephant (which tends to
produce small accelerations) offsets the influence of the
greater force It is the force/mass ratio which determines
the acceleration..
• The greater mass of the
elephant requires the
greater force just to
maintain the same
acceleration as the
feather.
• We say that mass and
acceleration are inversely
proportional. A large
mass will accelerate
slowly, while a small
mass will accelerate
quickly with the same
force.
• Other forces are affected by the area the force is applied to.
How does a snow shoe work?
• Because your mass and the acceleration due to gravity do not
change, the force you apply to the ground is the same with each
step.
• So why then can you walk across deep snow without sinking in
a snow shoe and not in a regular boot?
• The snow shoe allows the force of your step to be applied over
a large surface area.
• The force per unit area is a called pressure.
Inertia, Gravity and Satellites
4
• Satellites require great
speeds to avoid crashing!
– Altitude determines it speed
– a satellite in low orbit (about
800km/497mi) from the
Earth is exposed to an
immense amount of gravity
– has to move at considerable
speed to keep from crashing
• Gravity is important to keep
the satellite from moving off
into space.
4) From: Satellite Orbits http://www.eduspace.esa.int/subtopic/default.asp?document=297
• As the satellites are in
orbit outside the
atmosphere there is no
air resistance, and
therefore, the speed of
the satellite is constant.
• If orbiting inside the
atmosphere, the
satellite must overcome
air resistance (must be
able to speed up when
it slows down because
of air resistance)4.
• Satellites are both
natural (the moon) and
man made.
Newton’s 3rd Law
• Whenever one object exerts a force on
a second object, the second object
exerts an equal but opposite force on
the first object.
• Newton’s Third Law says that for
every action there is an equal but
opposite reaction.
• There is a pair of forces acting on the two
interacting objects.
• The size of the forces on the first object equals
the size of the force on the second object.
• The direction of the force on the first object is
opposite to the direction of the force on the
second object.
• Forces always come in pairs - equal and opposite
action-reaction force pairs.
Rifle has Ma
Bullet is Shot Out
by force from gun
powder
Bullet
has
mA
• Have you ever shot a rifle and felt the
kickback? Where does that come from and
how does this help us explain how a rifle
works?
• The rifle shoots the bullet with a force and the
bullet pushes the rifle back with the same
force. Because the rifle has a much larger
mass than the bullet, it will accelerate much
less than the bullet.
What about two forces in
opposite directions?
Me
You
• I hit a football and you hit a football in the opposite
direction.
• The two opposite forces “cancel” each other out and
the ball goes nowhere.
• The football will give us both a reaction force though.
Work &
Energy
WORK
WORK: It is used by physicists to measure something that
is accomplished. So it results in the equation:
Work = Force x displacement
The symbol for work is the variable = W
W=(F)(d)
You must move something (d) with a force (F) to
accomplish work.
Is work being done?
Pushing a car.
Attempting to lift 2,000,000 N.
Swimming in a rip current.
WORK
SO WHAT IF I PUSH ON A WALL THAT
DOES NOT MOVE? HAVE I DONE
WORK?… NO! HAVE I USED
ENERGY?... YES! WHAT IS ENERGY?
UH OH… another definition coming…
Energy…
• …is the ability to make
things move
The seven types of
energy…
• Chemical - gasoline,
• Light – flash light,
• Heat – burner on a stove,
• Nuclear - sun,
• Mechanical - car,
• Sound – music on the radio,
• Electrical - lightning
POTENTIAL ENERGY
How do you “store up energy?... There are two
kinds we study…
GPE -
GRAVITY POTENTIAL ENERGY: If you put an object up in
the air… gravity will pull it down and make it move some
distance… WORK will be done… an object is moved some
displacement… GPE = mgh… mg=force gravity, h=height… the
heavier the object is, the more force on it, the higher it is, the
further down it moves…
GPE = mgh
EPE - ELASTIC POTENTIAL ENERGY:
This is stored in a spring
or rubber band. The stronger the spring, or the further you stretch
it, the more work it can do. So, the EPE=(1/2)(k)(x2) … k = how
strong the spring is, and x= how far you stretch it…
EPE=(1/2)(k)(x2)
KINETIC ENERGY
KINETIC ENERGY = KE: This is moving energy.
Something that is moving will collide and crash into
another object, and move it a distance,… SO, the
energy that it has, will be equal to how BIG it is, m
(mass), and how FAST, v (velocity), it is moving….
KE = (1/2)(m)(v2)
Definitions
• Kinetic Energy: the energy
of motion
• KE = ½ mv2
• Potential Energy: stored
energy
• PE = mgh
A Roller Coaster
A roller coaster speeds
along its track. It has
kinetic energy because it is
moving.
A Roller Coaster
As it slows to a stop at
the top of a hill, it has
potential energy because of
where it is. It has the
potential to move because
it is above the ground and
has somewhere to go.
• Substances like wood, coal,
oil, and gasoline have stored
energy because of their
chemistry – they can burn
• Stored energy is potential
energy
NEW FORMULAS
W=(F)(d)
EPE=(1/2)(k)(x2)
GPE=(m)(g)(h)
KE=(1/2)(m)(v2)
ENERGY is what you “can do”………
WORK is what you “do do”………
and isn’t work doo-doo?
Calculating Work
F
d
m
A mass is being pulled to the right by a force, F , it
is moving to the right so that the displacement
is d… BUT is ALL of the force, F , doing
work?.... NO…. because some of the force is
lifting up in the positive +y direction
This means that the part of F that is pulling to the
right in the +x direction is doing work, because
that is the way the box is moving…
Calculating Work
F
d
m
What about the other forces on the box like weight, mg,
pulling down, or the F-normal, of the ground pushing
up…. NO… they do NO WORK, because the box is not
moving up or down….
Calculating Work
F
d
m
• What about F-friction, is it doing work?... YES…
BUT WAIT… THE FRICTION FORCE IS NOT IN
THE SAME DIRECTION THE BOX IS MOVING!!
IT IS TO THE LEFT!!
• This force is fighting the work being done by F. It is
doing what we call negative work because it is being
done in the OPPOSITE DIRECTION THAT THE
OBJECT IS MOVING…
Calculating Work
F
d
m
• FINALLY, we can find the TOTAL WORK, Wt,
done on the box…. It is the positive work done by F
plus the negative work done by friction Ff… Wt =
W - Wf
QUICK OVERVIEW ON WORK….
1)Work equals Force x displacement… W =
(F)(d)
2)Work is measured in Nm called Joules, or J
3)Work is positive if the force, F, is in the same
direction as the displacement
4)Any force that pushes on the object, but does
not move the object in the direction it is
pushing… does NO work
5)Any force that pushes in the opposite direction
that the object is moving, (especially friction),
does negative work
• Potential Energy can be changed
into Kinetic Energy
• Also Kinetic Energy can be
changed into Potential Energy
KE and PE are conserved!
KEfinal + PEfinal = KEinitial + PEinitial
Momentum and Impulse
Momentum and Impulse
• Momentum describes the motion of an object before and
after a collision
• Common sense tells us that when you collide with another
object or person… HOW MUCH you feel that collision, or
how much it hurts!... Depends on two things:
– 1) How big the object was that hit you
– 2) How fast it was going when it hit you
• But this is PHYSICS: 1) MASS (in kilograms) is a
measure of the object’s size, and 2) VELOCITY (in m/s)
is a measure of the object’s speed
• Formula for momentum is P = mv (YES… the
variable P is momentum)
Momentum and Impulse
• Impulse is what happens during a collision… It is measured by the force
during the collision… and the time, (how long), that collision occurs…
• Formula for Impulse is: I = (F)(t) (I is the variable for Impulse)
• There is ANOTHER way to measure Impulse …
• Impulse = the change in momentum… in terms of common sense, this
means that if an object’s momentum changes… you put an impulse on it
• Formula for Impulse is: I = Δmv = (mvf – mvi) How does this work?
• Formula I = (F)(t) = (mvf – mvi)
Momentum and Impulse
• CONSERVATION OF MOMENTUM:
• CONSERVATION means that the momentum of ALL the objects
BEFORE the collision, will EQUAL the momentum of ALL the
objects AFTER the collision…so… the total
momentum is NOT lost, only transferred
• All right… There are TWO kinds of collisions: ELASTIC collisions,
where the two objects hit and bounce apart…. Or…. INELASTIC
collisions, where the two objects hit and stick together….
• Formula: for an ELASTIC COLLISION is:
m1v1  m2 v2  m1v1'  m2 v2'
•
Formula: for an INELASTIC COLLISION is:
m1v1  m2 v2  (m1  m2 )v '
Work Done by a Spring
• Work done by a spring is different… WHY?...
Because the more you displace it, the MORE
force it takes to do it… SO… you can not just
multiply F x d, because F gets bigger as you
stretch it…. F IS CHANGING!... OK… so
how do you handle this?
Work Done by a Spring
• Let’s take a spring that is not
stretched or compressed, we will call
its length, Lo.
• So Lo is how long the spring is when
it is not stretched or compressed.
• Look at the diagram…. x is called
the deformation, it is how far you
stretch or compress the spring from
its original length, measured in
meters, m.
Work Done by a Spring
• If we are going to write a formula for the work
done by a spring, or the potential energy
stored in a spring, we have to know HOW
STRONG IS THE SPPRING?
• How do you measure this? In words it is
“how much force does it take to stretch or
compress the spring”…. The scientist Hooke
gave us a formula: F = kx
• Simply, if we rearrange this formula: k =
F/x…. What does this mean in words?....
• The strength of a spring, k, is measured by
HOW MANY NEWTONS OF FORCE, F, it
takes to stretch (or compress) a spring,
divided by the AMOUNT YOU STRETCH OR
COMPRESS IT, x (the deformation)…
Work Done by a Spring
• SO…. How much WORK is done on a spring?...
Or How much ENERGY is stored in a spring?...
They are the same!...
• WORK on a spring, OR ENERGY stored in a
spring….

Wspring = EPE (Elastic Potential Energy) = (1/2)(k)(x2)
CONSERVATION OF ENERGY
FORMULA
1) Is there any GPE, gravity potential energy, mgh?
2) Is there any EPE, elastic potential energy,½kx2 ?
3) Is there any KE, kinetic energy, ½mv2?
KEfinal + PEfinal + EPEfinal = KEinitial + PEinitial + EPEinitial
POWER
• POWER… What is it? There seems to be political
power, military power, personal power, and automobile
engine power to mention a few….
• Physics will concern itself with mechanical power… So
what is that?.... In words it means “how fast you do
work”….. So the formula for power is P = W/t
• Let’s see if this makes sense…. W, work is in the
numerator, so if you do more work in the same amount
of time, it takes more power… t, time is in the
denominator, so if you do the same amount of work in
less time, it takes more power… finally, if you do more
work in less time, you need a lot more power!
Work and Simple
Machines
History of Work
Before engines and motors were invented, people
had to do things like lifting or pushing heavy loads by
hand. Using an animal could help, but what they really
needed were some clever ways to either make work
easier or faster.
Simple Machines
Ancient people invented simple
machines that would help them
overcome resistive forces and allow
them to do the desired work against
those forces.
Simple Machines
• A machine is a device that helps
make work easier to perform by
accomplishing one or more of the
following functions:
– transferring a force from one place to
another,
– changing the direction of a force,
– increasing the magnitude of a force, or
– increasing the distance or speed of a
force.
Simple Machines
•
The six simple
machines are:
–
–
–
–
–
–
Lever
Wheel and Axle
Pulley
Inclined Plane
Wedge
Screw
Mechanical Advantage
• It is useful to think about a machine
in terms of the input force (the force
you apply) and the output force
(force which is applied to the task).
• When a machine takes a small input
force and increases the magnitude of
the output force, a mechanical
advantage has been produced.
Mechanical Advantage
• Mechanical advantage is the ratio of output force
divided by input force. If the output force is
bigger than the input force, a machine has a
mechanical advantage greater than one.
• If a machine increases an input force of 10
pounds to an output force of 100 pounds, the
machine has a mechanical advantage (MA) of 10.
• In machines that increase distance instead of
force, the MA is the ratio of the output distance
and input distance.
• MA = output/input
No machine can increase
both the magnitude and
the distance of a force at
the same time.
The 3 Classes of Levers
• The class of a
lever is
determined by the
location of the
effort force and
the load relative to
the fulcrum.
First Class Lever
• In a first-class lever the fulcrum is
located at some point between the
effort and resistance forces.
– Common examples of first-class
levers include crowbars, scissors,
pliers, tin snips and seesaws.
– A first-class lever always changes the
direction of force (I.e. a downward
effort force on the lever results in an
upward movement of the resistance
force).
Fulcrum is between EF (effort) and RF (load)
Effort moves farther than Resistance.
Multiplies EF and changes its direction
Second Class Lever
• With a second-class lever, the load is
located between the fulcrum and the effort
force.
– Common examples of second-class levers
include nut crackers, wheel barrows, doors,
and bottle openers.
• A second-class lever does not change the
direction of force. When the fulcrum is
located closer to the load than to the
effort force, an increase in force
(mechanical advantage) results.
RF (load) is between fulcrum and EF
Effort moves farther than Resistance.
Multiplies EF, but does not change its direction
Third Class Lever
• With a third-class lever, the effort
force is applied between the fulcrum
and the resistance force.
• Examples of third-class levers include
tweezers, hammers, and shovels.
– A third-class lever does not change the
direction of force; third-class levers
always produce a gain in speed and
distance and a corresponding decrease
in force.
EF is between fulcrum and RF (load)
Does not multiply force
Resistance moves farther than Effort.
Multiplies the distance the effort force travels
To find the MA of a lever, divide the output force by the input force, or
divide the length of the resistance arm by the length of the effort arm.
Wheel and Axle
• The wheel and axle is
a simple machine
consisting of a large
wheel rigidly secured
to a smaller wheel or
shaft, called an axle.
• When either the
wheel or axle turns,
the other part also
turns. One full
revolution of either
part causes one full
revolution of the
other part.
Pulley
• A pulley is said to be a fixed
pulley if it does not rise or fall
with the load being moved. A
fixed pulley changes the
direction of a force; however, it
does not create a mechanical
advantage.
• A moveable pulley rises and
falls with the load that is being
moved. A single moveable
pulley creates a mechanical
advantage; however, it does not
change the direction of a force.
• The mechanical advantage of a
moveable pulley is equal to the
number of ropes that support the
moveable pulley.
• For example, below are four puly systems. If we
divide the input force (the amount of force needed to
• pull on the rope) into the weight we are trying to lift,
we will have the mechanical advantage for the
• system. The systems below have a mechanical
advantage of 1, 2, 3, and 4 respectively.
100 N / 1 = 100 N
100 N / 2 = 50 N
100 N / 3 = 33.3 N
100 N / 4 = 25 N
Inclined Plane
• An inclined plane
is an even sloping
surface. The
inclined plane
makes it easier to
move a weight
from a lower to
higher elevation.
Inclined Plane
• The mechanical
advantage of an
inclined plane is equal
to the length of the
slope divided by the
height of the inclined
plane.
• While the inclined
plane produces a
mechanical
advantage, it does so
by increasing the
distance through
which the force must
move.
Although it takes less force for car A to get to the top of the ramp,
all the cars do the same amount of work.
A
B
C
Wedge
• The wedge is a
modification of the
inclined plane. Wedges
are used as either
separating or holding
devices.
• A wedge can either be
composed of one or two
inclined planes. A double
wedge can be thought of
as two inclined planes
joined together with their
sloping surfaces outward.
Screw
• The screw is also
a modified version
of the inclined
plane.
• While this may be
somewhat difficult
to visualize, it may
help to think of the
threads of the
screw as a type of
circular ramp (or
inclined plane).
Efficiency
• We said that the input force times the distance equals
the output force times distance, or:
Input Force x Distance = Output Force x Distance
However, some output force is lost due to friction.
• The comparison of work input to work output is called
efficiency.
• No machine has 100 percent efficiency due to friction.
Complex Machines
• Complex machines are made from
combining many simple machines to
perform
• complex tasks. A car contains many
varieties of simples machines
combined together to make a
complex machine.
A Complex Machine
Electricity & Magnetism
Static, Currents, Circuits
Magnetic Fields & Electro Magnets
Motors & Generators
Electrons…
• Are located on the outer edges
of atoms…they can be moved.
• A concentration of electrons in
an atom creates a net negative
charge.
• If electrons are stripped away,
the atom becomes positively
charged.
What is this electrical potential
called?
• Static Electricity
-
-
- -
+
++
++
Static Electricity
• The build up of an electric
charge on the surface of an
object.
• The charge builds up but does
not flow.
• Static electricity is potential
energy. It does not move. It is
stored.
Static Discharge…
• Occurs when there is a loss of
static electricity due to three
possible things:
• Friction - rubbing
• Conduction – direct contact
• Induction – through an
electrical field (not direct
contact)
Electricity that moves…
• Current: The flow of electrons
from one place to another
(symbol = I).
• Measured in amperes (amps)
• Kinetic energy
How can we control currents?
• With circuits.
• Circuit: is a path for the flow of
electrons. We use wires.
There are 2 types of currents:
• Direct Current (DC) – Where
electrons flow in the same
direction in a wire.
• Alternating Current (AC) –
electrons flow in different
directions in a wire
There are 2 types of circuits:
• Series Circuit: the components
are lined up along one path. If
the circuit is broken, all
components turn off.
Series Circuit
There are 2 types of circuits:
• Parallel Circuit – there are
several branching paths to the
components. If the circuit is
broken at any one branch, only
the components on that branch
will turn off.
Parallel Circuit
Conductors vs. Insulators
• Conductors – material through
which electric current flows
easily.
• Insulators – materials through
which electric current cannot
move.
Examples
• Conductors:
–Metal
–Water
• Insulators:
–Styrofoam
–Rubber
–Plastic
–Paper
What is Resistance (R)?
• The opposition to the flow of an
electric current, producing heat.
• The greater the resistance, the
less current gets through.
• Good conductors have low
resistance.
• Measured in ohms (Ω).
What Influences Resistance?
• Material of wire – aluminum and
copper have low resistance
• Thickness – the thicker the wire the
lower the resistance
• Length – shorter wire has lower
resistance
• Temperature – lower temperature
has lower resistance
What is Voltage (V)?
• The measure of energy given to
the charge flowing in a circuit.
• The greater the voltage, the
greater the force or “pressure”
that drives the charge through
the circuit.
Difference b/t Volts and Amps
• Example – you could say that…
–Amps measure how much water
comes out of a hose.
–Volts measure how hard the
water comes out of a hose.
Ohm’s Law
• Voltage = Resistance x Current
• V = IR
Magnetism
What is Magnetism?
• Magnetism is the attraction of a
magnet to another object.
What are Magnetic Poles?
• Magnets have two ends, called
magnetic poles.
• Magnetism is strongest at the
poles of a magnet.
S
S
N
Magnetic Poles
• Magnetic poles that are alike repel
each other.
• North repels North
• South repels South
• Poles that are not alike attract each
other
• North attracts South
• South attracts North
What is a Magnetic Field?
• The magnetic force exerted in
the region around the magnet is
the magnetic field.
• This allows magnets to interact
without touching.
What are Magnetic Field
Lines?
• Magnetic Field Lines spread out
from one pole, curve around the
magnet, and return to the other
pole.
S
N
What do atoms have
to do with it?
• All atoms have magnetic fields
because of the charged particles
inside.
• Most atoms’ magnetic fields point
in random directions, so they all
cancel each other out.
What do atoms have
to do with it?
• In magnetized material, all or
most of the magnetic fields are
arranged in the same direction.
• A material that keeps its
magnetism is called a permanent
magnet.
What do Electric Currents
have to do with Magnets?
• An electric current produces a
magnetic field.
• The direction of the current
determines the direction of the
magnetic field.
What is an Electromagnet
• An Electromagnet is a strong
magnet that can be turned on
and off.
• It consists of a current-carrying
wire wrapped around an iron
core.
Characteristics of
Electromagnets
• Strength depends on the number of
coils and the size of the iron core.
• The greater the number of turns the
coil has the stronger the magnet
will be.
• The closer the coils are the
stronger the magnet will be.