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Universal Forces
Chapter 12.4
Universal Forces
Observations of planets, stars, and galaxies
strongly suggest four universal forces exist
throughout the universe.
• Electromagnetic
• Strong nuclear
• Weak nuclear
• Gravitational
Forces act over a distance between particles of
matter:
- The particles don’t need to be in contact
- Forces are affected by the distance between
the particles of matter
Electromagnetic Forces
Electromagnetic force is associated with
charged particles.
Electric and Magnetic forces are the only forces
that can both attract and repel
Electric Force
Acts between charged objects or particles
(electrons and protons)
Objects with opposite charges attract each
other
Objects with like charges repel one another
Clothes often acquire
electric charges in the drier.
Cotton loses electrons
easily = + charge
Polyester gains electrons
easily = - charge
Clothes with opposite
charges tend to cling
together.
http://funny-pictures.feedio.net/static-electricity-cat-funny-picture-lol-meme/imglols.com*wpcontent*main*2010_09*static-electricity-cat.jpg/
Magnetic Force
Act on certain metals, poles of magnets, moving
charges.
http://www.b-ecochic.com/wooden-toy-train-set.html
http://anjungsainssmkss.wordpress.com/category/sains-ting-3-form-3-pmr/chapter-7electricity/
Nuclear Forces
Two forces, strong nuclear and weak nuclear, act
within the nucleus to hold it together.
physics.tutorvista.com
Gravitational Force
Gravitational force = an attractive force that
acts between any two masses.
Newton’s law of universal gravitation states that
every object in the universe attracts every other
object.
You exert a gravitational
force on your book and
your book exerts a
gravitational force on
you.
You don’t notice this
because the masses are
so small.
It takes a HUGE
mass to exert a
large gravitational
force.
The gravitational force
between two objects
depends on their mass
and distance.
A: two masses, X & Y,
attract each other
B: larger mass of X
results in larger
gravitational force
C: an increase in distance
decreases the
gravitational force
Gravity
Gravity is the weakest universal force but is the
most effective over large distances.
Gravity:
- Holds you on Earth
- Keeps the moon in orbit around Earth
- Keeps the planets in orbit around sun
- Keeps stars in orbit in galaxies
Gravity (minute physics)
The Moon
How is the moon kept in orbit around the Earth?
Moon has inertia: move along a straight path
until acted on by a force (Earth’s gravitational
pull)
Centripetal force = center-directed force that
continuously changes the direction of an object
to make it move in a circle
Tides
The gravitational pull from the moon produces
two bulges in the Earth’s oceans. Earth rotates
under these bulges which creates 2 high tides
and 2 low tides each day.
tides
Review
1. Which of the following is NOT one of the
universal forces?
a.
b.
c.
d.
Strong nuclear
Gravitational
Electromagnetic
Magical
Review
2. Which forces are the only forces that can
both attract and repel?
a. electric and nuclear
b. magnetic and nuclear
c. magnetic and gravitational
d. electric and magnetic
Review
3. The gravitational force between two objects
depends on the objects’…
a. masses and distance
b. masses and weight
c. distance and volume