Newtons Second Law of Motion

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Newtons Second Law of Motion
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Bell Work

• Identify three forces acting on a speeding
  bullet.
• Why do cars sometimes skid going around corners
  on icy roads?

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Objectives

• Define and apply Newtons second law of motion to
  real life situations.
• Relate the acceleration of an object to the mass
  of the object and the force applied to the object.

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Newtons Second Law of Motion

• This law states that an unbalanced force on an
  object causes the object to accelerate in the
  direction of the force.

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Force of wind
These forces are unbalanced so the boat
accelerates in the direction of the unbalanced
force.
20-30 mph
Air/Water Resistance
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Gravity
Unbalanced Forces
Table
If gravity becomes greater than the upward force
of the table, the papers will accelerate downward.
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Wagon moves this way
Unbalanced
Force
Applied
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Force, Acceleration, and Mass

• The greater the force applied to a given object,
  the greater its acceleration.

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Force, Acceleration, and Mass

• For a given force, the greater the mass of an
  object, the smaller its acceleration and
  vice-versa.

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Newtons Second Law in Real Life

• Why would a truck take longer to accelerate when
  the driver hits the gas if it were loaded with
  bricks than if it were empty?
• How might you design a car to achieve maximum
  acceleration?

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Newtons Second Law in Real Life

• Using Newtons second law of motion, explain why
  larger trucks usually need more distance to stop
  than do smaller trucks.

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Science, Technology, Sports

• Friction is the main force that slows the speed
  of athletes in sports such has skiing, swimming,
  cycling, speed skating, and running. How can
  these athletes combat the effects of friction?

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Formula for Newtons Second Law of Motion

• Newtons second law of motion can be expressed by
  the formula F ma.
• F stands for force, m stands for mass, and a
  stands for acceleration.

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Formula for Newtons Second Law of Motion

• According to this formula, if the force is
  constant and the mass increases, what will happen
  to acceleration?

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Question

• Identical twins are riding in identical wagons. A
  friend gives the first wagon a stronger push than
  the second. Which twin will experience greater
  acceleration?

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Question

• Would a car towing a boat take less, the same, or
  more time to accelerate than it would without the
  boat? Explain.

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Question

• What will happen to the acceleration of an object
  if the mass decreases and the force is constant?

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Question

• If two identical objects accelerate at the same
  rate, what must be true of the force applied to
  each object?

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Review

• Use Newtons second law of motion to explain why
  a free-falling object accelerates.
• How is the acceleration of an object affected by
  the force applied to it?

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Challenge

• Using the formula a f/m, explain why all
  objects in free fall have the same acceleration,
  regardless of mass.