Forces

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Chapter 12

• Forces

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Section 12.1

• Newtons First and Second Laws

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Newtons First Law

• An object at rest remains at rest and an object
  in motion maintains its velocity unless it
  experiences an unbalanced force.

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Inertia

• The tendency of an object to remain at rest or in
  motion with a constant velocity.

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Newtons Second Law

• The unbalanced force acting on an object equals
  the objects mass times its acceleration.
• Force mass x acceleration

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• Force is measured in Newtons.
• 1 N 1 kg x 1 m/s²
• One Newton 0.225 lb.
• 1 lb 4.448 N

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Section 12.2

• Gravity

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Gravity

• The attraction between two particles of matter
  due to their mass.

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Gravitational force depends on

• Mass the greater the mass of an object is, the
  larger the gravitational force it exerts.

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• Distance the greater the distance between two
  objects, the lower the gravitational force
  becomes.

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• Mass is a measure of the amount of matter in an
  object.
• Weight is different from mass.
• Weight is the gravitational force an object
  experiences due to its mass.

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Mass and Weight

• Mass is a measure of the amount of matter in an
  object.
• Weight is different from mass.
• Weight is the gravitational force an object
  experiences due to its mass.

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• Weight mass x free-fall acceleration
• W mg
• SI unit for weight is the Newton.

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• Free-fall acceleration near Earths surface is
  constant.
• All objects on Earth accelerate at 9.8 m/s²

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Free fall

• The motion of a body when only the force of
  gravity is acting on it.

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• Astronauts in orbit are in free fall.
• Are they weightless?

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• Astronauts in space experience apparent
  weightlessness.
• They are in free fall.

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Projectile Motion

• The curved path followed by an object that is
  thrown, launched, or otherwise projected near the
  surface of Earth.

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• Projectile motion has two components
• Horizontal and vertical.
• Combined, they form a curved path.

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Orbiting is projectile motion.
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Terminal Velocity

• The maximum velocity reached by a falling object
  that occurs when the resistance of the medium is
  equal to the force due to gravity.

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Section 12.3

• Newtons Third Law

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Newtons Third Law

• For every action force, there is an equal and
  opposite reaction force.

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Momentum

• Momentum mass x velocity.
• A quantity defined as the product of an objects
  mass and its velocity

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The Law of Conservation of Momentum

• The total amount of momentum in a system is
  conserved.

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Identify as speed, velocity, or momentum

• 88km/h
• 10m/s straight up.
• 18 kg x m/s down.
• 19m/s to the west.

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Momentum Equation

• P mv
• MomentumMass x Velocity

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• Momentum increases as mass and velocity increase.