Chapter 3 Forces

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Chapter 3 Forces

• Mr. Robinson
• Science Instructor

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Section 1 Newtons 2nd Law

• The acceleration of an object depends on its mass
  as well as the force exerted on it.
• Force, mass, and acceleration
• Example Softball with mass of 0.20kg and
  baseball with mass of0.14kg
• Softball has less velocity after it leaves your
  hand

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Newtons 2nd Law of Motion

• Newtons 2nd law of motion describes how force,
  mass, and acceleration are connected
• The net force acting on an object causes the
  object to accelerate in the direction of the net
  force

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Motion Equation
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Newtons 2nd Law

• The SI units, the unit of mass is kilogram (kg),
  and the unit of acceleration is meters per second
  squared (m/s2)
• Force has the units kg x m/s2 is called the
  Newton (N)

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Friction

• Friction is the force that opposes motion between
  two surfaces that are touching each other
• The amount of friction between two surfaces
  depends on two factors
• The kinds of surfaces
• The force pressing the surfaces together

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What causes friction

• All surfaces have dips and bumps
• Areas where the highest bumps come in to contact
  with each other
• Areas where the bumps stick together are called
  microwelds
• Microwelds are the source of friction

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Microwelds
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Sticking Together

• The stronger the force pushing the two surfaces
  is, the stronger these microwelds will be
• More surface bumpsmore contact
• To break these microwelds and move one surface
  over the other, a force must be applied

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Static Friction

• A force that resists the effort to move something
  is called friction
• Static friction is the friction between two
  surfaces that are not moving past each other

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Static Friction
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Sliding Friction

• Sliding friction is the force that opposes the
  motion of two surfaces sliding past each other
• Sliding friction is caused by microwelds
  constantly breaking and then forming again as the
  box slides along the floor

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Rolling Friction

• The friction between a rolling object and the
  surface it rolls on

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Air Resistance

• Acts on objects on objects that fall through the
  air
• The force of air resistance is in the opposite
  direction to the force of gravity
• Air resistance affects anything that moves in
  earths atmosphere
• Air resistance is pushing down

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Air resistance
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Air Resistance

• The amount of air resistance on an object depends
  on the speed, size, and shape of the object
• If no air resistance is present, then a feather
  and a apple will fall at the same rate

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Terminal Velocity

• When the forces on the falling object are
  balanced and the object no longer accelerates
• When it falls with a constant speed called the
  terminal velocity

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Section 2 Gravity

• Anything that has mass is attracted by the force
  of gravity
• Law of Gravity-any two masses exert an attractive
  force on each other
• Attractive Force depends on two factors
• Mass of the two objects
• Distance between the objects

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Gravity
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Gravitational Acceleration

• The gravitational attraction of Earth causes all
  falling objects to have an acceleration of
  9.8m/s2
• Newtons second law, the net force, mass, and
  acceleration are related according to the
  following formula
• F ma
• Fm X 9.8m/s2

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Weight

• The gravitational force on an object is called
  the objects weight
• Gravitational Forcemass x acceleration
• WeightNewton (N)

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Weight and Mass

• Weight and mass are not the same
• Weight is a force
• Mass is a measure of the amount of matter an
  object contains
• Weight and mass are related

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Weight and Mass
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WeightlessnessFree Fall
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Horizontal and Vertical Motions

• Gravity exerts an unbalanced force on a
  projectile, changing the direction of its path
  from only moving forward to a forward and
  downward force

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Centripetal Force

• Centripetal Acceleration toward the center of a
  curved or circular path
• Centripetal means move toward the center
• For a ball to be accelerating toward the center,
  an unbalances force called centripetal force

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Centripetal Force

• When a car rounds a sharp curve on a highway,
  the centripetal force is the friction between the
  tires and the road surface
• If road is wet or icy tires lose their grip

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Projectile Motion

• Anything thats thrown or shot through the air is
  called a projectile
• Projectiles follow a curved path due to Earths
  gravity
• Projectiles have horizontal and horizontal
  velocities

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Satellites

• A satellite is anything that moves around another
  body in a generally circular path called a orbit
• Earth and the other planets are satellites
  because they orbit the Sun
• The International Space Station orbits the Earth
  is called Artificial Satellite

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Section 3 The 3rdLaw of Motion

• For every action there is a equal and opposite
  reaction force
• When a force is applied in nature, a reaction to
  it occurs
• Example shooting a gun and the kick back of the
  gun