Transcript Universal Forces - St. Paul School

Universal Forces
Section 3.5
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What do we know?
• What force keeps the Earth moving around the
sun?
• What do lightening and static cling have in
common?
Common Forces
• Give a reason why each of the following
happens.
• A ball that rolls off the table falls to the floor.
• A cabinet door with a magnet on the latch stays
closed.
• Clothes from the dryer cling to each other.
Universal Forces
• Forces act upon you no matter where you are.
• Even if you traveled to a distant planet, four of the
universal forces that you feel on Earth would be
present there.
• Universal forces:
•
•
•
•
Gravitational
Electromagnetic
Strong Nuclear
Weak Nuclear
• Table 3.1 on page 73 shows the strengths of these
universal forces.
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Gravitational Force
• Objects of any size are pulled toward each other
by gravitational force.
• Don’t notice it between small objects because it is
the weakest of the universal forces.
• Strength of the gravitational force depends on the
amount of mass in an objects and the distance
between the objects.
• Planets, stars, and galaxies are so large that their
gravitational force affects other objects in space.
http://ramsayscience5.wikispaces.com/file/view/gravity.gif/184623245/323x257/gravity.gif
Gravitational Force in
Space
• Gravity keeps the planets in orbit around the
sun.
• It also keeps the stars in orbit in their galaxies.
• Gravitational force of the Earth on the Moon
keeps the Moon in its orbit around the Earth.
• Gravitational force of the Moon on the Earth
causes the ocean tides to rise and fall.
http://science8morris.weebly.com/uploads/1/4/2/3/14239239/4783377.jpg
Gravity and the Solar
System
• Newton proposed that the sun exerts a
gravitational force on the Earth and its Moon,
but also on the other planets.
• Because of this gravitational force, the Earth
and other planets in the solar system orbit
around the sun.
• Each planet moves in an elliptical orbit around
the sun.
http://creationwiki.org/pool/images/thumb/b/b7/Solar_system_orbital_track.jpg/350px-Solar_system_orbital_track.jpg
What do you see?
• Look at Figure 3.17 on page 74:
• Which planet’s surface gravity is more than
twice as great as the Earth’s gravity?
• Which planets are between Earth and the sun?
• Which planets are beyond Earth?
• What would happen if a spaceship came very
close to a planet? Why?
• On what objects do the planets exert a
gravitational force like the sun does on them?
Law of Universal
Gravitation
• Newton’s law of universal gravitation states that every
object in the universe attracts every other object.
• Gravitational force between two objects depends on the
mass of each object and the distance between them.
• Gravitational force between ordinary objects on Earth is
extremely small (too small to measure).
• Gravitational force between earth and moon is easily
measured because they both have a large mass.
• Gravitational force is also affected by distance. (Saturn
doesn’t affect gravitational pull on your textbook because
its far away.)
• But Earth’s gravitational pull is very noticeable.
http://upload.wikimedia.org/wikipedia/commons/d/d1/GPB_circling_earth.jpg
The Earth-Moon System
• Newton realized that the gravitational force also
applies to the moon.
• Newton also predicted that objects on the moon
weigh less than they do on Earth due to the fact
that the moon is 81 times less massive.
• Earth and Moon are affected by each other’s
gravitational force.
• As the moon orbits the Earth, the Moon pulls on
surface water of the Earth.
• Gravitational pull of the Moon causes the ocean
waters nearest the moon to bulge (tides).
http://images.wisegeek.com/moon-and-earth-in-orbit.jpg
What do you think?
• Looking at Figure 3.18 on page 76:
• Why are the tides stronger when the sun and
the moon are in line?
• What causes the neap tides?
Electromagnetic Forces
• Electromagnetic forces are really two different
forces that are closely related:
• Electric Force
• Magnetic Force
• Both of these forces may attract or repel.
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Electromagnetic Forces
• Electric Force:
• Exists between charged particles.
• Objects with opposite charges attract; objects with
like charges repel.
• Much stronger than gravitational force.
• You are constantly affected by this force.
• Causes some objects to come together and some
objects to stay apart.
• Holds together the particles that make up matter.
• Causes static, creates lightening, and creates
electricity.
http://cf067b.medialib.glogster.com/media/31/31c5039e2b2c388fabcd94e7fa39e47e781c390f220ba5ea17e0cb282c41ac72/electrical-force-jpg.jpg
Electromagnetic Forces
• Magnetic force:
• Similar to electric force.
• Acts between two magnets
• Attracts or repels that same as an electric force.
• Magnetic force and electric forcer interact in
motors and other devices.
• For example, the carbon granules in the receiver
of your telephone change the sound of your
voice into electric signals. These electric signals
travel through the wires from your home to that
of your friend where a magnet in your friend’s
telephone receiver changes the electric signals
back into the sound of your voice.
http://images.tutorvista.com/cms/images/83/magnet.PNG
Nuclear Forces
• All matter is made up of tiny particles called
atoms.
• Atoms are made up of 3 subatomic particles:
proton, neutron, and electron. Protons and
Neutrons are in the nucleus of the atom.
• Nuclear Forces- forces that act on the nucleus.
http://upload.wikimedia.org/wikipedia/commons/3/35/Nuclear_Force_anim_smaller.gif
Nuclear Forces
• Strong Nuclear Force:
• Holds the nucleus together.
• Without this force, protons and neutrons would
fly apart.
• These forces are very strong.
• Acts only over extremely short distances.
• If the forces are broken, huge amounts of
energy are released, which can be used to
produce electricity or a nuclear explosion.
http://www.online-sciences.com/wp-content/uploads/2015/04/strong-nuclear-force-3.jpg
Nuclear Forces
• Weak nuclear forces:
• Slightly weaker than the strong force.
• Acts over a short range, but affects all particles, not just
protons and neutrons.
• Can cause a neutron to decay into a proton, an electron,
and a third particle called an antineutrino.
• All particles that decay in this way are called
radioactive.
• Measurement of radioactive decay can be used to
reveal the age of a fossil.
• Some kinds of nuclear decay release harmful radiation
that can affect people and the environment.
http://www.green-planet-solar-energy.com/images/beta-decay.gif
What have we learned?
1. Name the four universal forces.
2. Explain the roles of the universal forces when
you heat food in an electric oven.
3. State why the gravitational force is important
to every object in the universe.
4. List some activities taking place in your
classroom. Classify each activity according to
the universal force that applies to it.