FORCES

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FORCES

• There once was a man with no arms

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1) Forces are a push or pull that

• changes an objects state of motion.
• Forces cause objects to accelerate

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2) Aristotle Aristotle

• Greek
• natural philosopher
• EARTH ,WIND,
• FIRE, WATER.
• Natural motion
• forced
• motion

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3) Galileo Galilei(1564-1642)

• Inertia, friction
• No force
• needed for
• motion

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4) Sir Isaac Newton (1642-1727)

• Father of Physics
• 3 Laws of motion
• Law of Gravitation
• EM color spectrum
• Calculus

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5) The four natural forces are

• 1) Strong nuclear force
• 2) Electromagnetic
• 3) Weak nuclear force
• 4) Gravity
• Gravity is the weakest of all natural forces.

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Newtons 1st Law of Motion is the Law of INERTIA
it states

• 7) that objects in motion remain in motion at a
  constant velocity and
• objects at rest remain at rest unless.
• acted on by an unbalanced force.

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INERTIA is

• Mass (means lazy in Latin)
• Mass is the amount of inertia an object
  possesses.
• Name an object with a lot of inertia

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9) Examples of inertia

• the earth, sun, Betelgeuse
• Name an object with a small amount of inertia

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• b) electron, proton, or neutron
• Name an object with a small amount of inertia a
  large volume.

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• Blimp / hot air balloon
• Name an object with a large amount of inertia a
  small volume.

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• Neutron star

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10) Can you lift, move or shake 1000 kg object in
space? (2200 lbs)

• NO!
• It is weightless but still has inertia.

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Newtons 2nd Law of Motion
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The Law of Acceleration

• Acceleration is proportional to force.
• Acceleration is inversely proportional to mass.
• 11) Force
• mass x acceleration

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F m x a
What would a force triangle look like?
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F is measured in kgxm/s214) kgxm/s2 is called a
newton 12) Dyne (dyn), kilopond (kp)English?
pound (lbs), poundal(pdl)
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13) A net force is the sum of all forces acting
on an object.

• positive negative

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13) Balanced unbalanced forces
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15) Weight is a force!!!

• Weight is not mass! The force of weight is caused
  by gravity.
• Gravity accelerates all objects at a rate of
  9.8m/s2

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The symbol for the acceler-ation due to gravity
is g g 9.8 m/s2 on earth

• w m x g

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Weight weight mass x gravitys
accelerationTidesBay of FundyOrbitsPerturbatio
ns
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16) Newtons 3rd Law
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• The Law of Interactions
• For every action force there is an
• _______ _____ reaction force.
• 17. Forces always occur in pairs. One is the
  action force the other is the reaction force.
  Equal opposite

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Bat ball
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Boy wagon

• bird

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Rocket in space
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Bullet rifle
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Ball falling to earth
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19) They are equal!

• 20) They occur on 2 different objects at exactly
  the same moment in time.

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Nobel Prize in Chemistry

• Each prize includes a
• check for 1.4 million,
• a diploma and a medal, which will be awarded by
  Sweden's King Carl XVI Gustaf at a ceremony in
  Stockholm on Dec. 10.

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Gravity
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1) I fain no hypothesis.

• There is a force of attraction between all
  objects in the universe that is proportional to
  the product of the masses and inversely related
  to the squared distance separating the center of
  masses.

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Universal Law of Gravitation

• 2) F G m1xm2 / r2
• where F is the magnitude of the
  gravitational force between the two point masses
• G is the gravitational constant
• Note G 6.67 x 10-11 N m2/kg2
• m1 is the mass of the first point mass
• m2 is the mass of the second point mass
• r is the distance between the two point masses

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• Falling All objects fall at
• 9.8 m/s2 on earth

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• Weight ? on earth w m x g

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• Orbits shapes of stars, planets moons

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Orbits Perturbations
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Planet X New Member of our Solar System

• The planet was discovered by the Samuel Oschin
  Telescope at the Palomar Observatory near San
  Diego, Calif., on Jan. 8, 2005.

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• Tides

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15 A) Gravity causes projectile motion

• A projectile is any object which once projected
  continues in motion by its own inertia and is
  influenced only by the downward force of gravity.
• Rocks, arrows, darts, bullets, etc
• Not jets, rockets, birds, missiles

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B) Aerodynamic, curved path, no external forces
other than gravity.

• C)

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• The paths of projectiles.
• This shape is called a PARABOLA

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Label the diagram
                                                                            
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Circular Motion
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8) CenTRIP-etal force is the force directed
towards the center of curved path.

• Centripetal means "center seeking" force.

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• 10) Straight line. No centripetal Force, no
  turning Straight line motion only.
• If the rope were to break the ball would travel
  in a
• straight line

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11) No or a small amount of gravity acting on an
object.

• 12) Spin an object at a rate of 9.8 m/s2

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• Artificial

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• Natural

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14) Military, communication, GPS, weather

• 15) Orbits decay

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FRICTION - slip happens!
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• Where did the physics student fall in the
  library?
• What do you call Star Wars jokes that rub you
  the wrong way?
• 2 cats slide off the roof which hits the ground
  first?
• Lighten up, friction can be a drag. (all puns are
  intended)

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16) Friction is the force that opposes motion.

• Friction is caused by the close contact of 2
  surfaces.

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17) Friction is electromagnetic
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18) 2 types of friction

• friction between two substances when both are at
  rest. Must be overcome before moving an object.

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Kinetic or Dynamic friction

• Friction when an object is moving. This friction
  resists changes in motion.
• Kinetic friction can be described 3 ways.

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• A) Sliding

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• b) Rolling friction

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• c) Fluid friction

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19) Is friction useful?

• yes, walking, grip, heat

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19) Is friction harmful?

• Yes abrasion, heat, machine wear

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20) To increase friction

• More weight or pressure
• More surface area (rougher)
• Change surface material
• (rubber, latex, or nylon)

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20) To decrease friction.

• Less weight or pressure.
• Smoother (polished) surfaces.
• Change type of friction.
• Use glass, metal, or teflon
• LUBRICATE!!!!

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21) Yes, friction opposes motion, causes negative
acceleration, requires more force.

• What about air? Aerodynamics

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• Weight-gravity, thrust-engine, drag-fluid
  friction, lift-Bernoulli's principle