Focus On Physical Science

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2.1 Combining Forces

• force
• contact force
• noncontact force
• net force
• unbalanced forces
• balanced forces
• Newtons first law of motion

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Force
2.1 Combining Forces

• When more than one force acts on an object, the
  combined effect is caused by the sum of all
  applied forces.

• A push or a pull on an object is a force.

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Contact and Noncontact Forces
2.1 Combining Forces

• A contact force is exerted only when two objects
  are touching.

• A noncontact force is exerted when two objects
  are not touching.

• Magnets exert a noncontact force on each other.

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Force is a Vector
2.1 Combining Forces

• Vectors have magnitude and direction.

• Force has a direction and a magnitude.
• Force is measured in Newtons.

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Combining Forces
2.1 Combining Forces

• When more than one force acts on an object, the
  forces combine.

• The combination of all the forces acting on an
  object is called the net force.

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Combining Forces in the Same Direction
2.1 Combining Forces

• Forces are vectors and require a reference
  direction.

• When forces in the same direction combine, the
  net force is in the same direction and the size
  of the force is the sum of the forces.

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Combining Forces in the Same Direction (cont.)
2.1 Combining Forces

• If two people push the dresser to the right, the
  forces are added together.

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Combining Forces in Opposite Directions
2.1 Combining Forces

• When forces in opposite directions combine, the
  net force is in the direction of the larger force.

• The size of the net force is the difference
  between the two forces.

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Combining Forces in Opposite Directions (cont.)
2.1 Combining Forces

• Two people exerting a force in opposite
  directions show how vectors combine to create net
  force.

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Unbalanced and Balanced Forces
2.1 Combining Forces

• If the net force on an object is not zero, it is
  an unbalanced force.

• If the net force on an object does equal zero, it
  is a balanced force.

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Balanced Forces
2.1 Combining Forces
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Balanced Forces and Motion
2.1 Combining Forces

• If two people push with the same force, the
  dresser does not move.

• The forces have the same magnitude.
• The forces are in opposite directions.
• The net force on the dresser is zero and the
  forces are balanced.
• The motion of the dresser does not change.

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Unbalanced Forces and Motion
2.1 Combining Forces

• Unbalanced forces change motion.

• If two people push with different force, the
  dresser moves.
• The forces have a different magnitude and are in
  opposite directions.
• The net force on the dresser is not zero and the
  forces are unbalanced.
• The dresser moves in the direction of the larger
  force.

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Newtons First Law of Motion
2.1 Combining Forces

• If the net force on an object is zero, the
  velocity of the object does not change.

• If the net force is zero and the object is at
  rest, it remains at rest.
• If the net force is zero and the object is
  moving, it continues to move in a straight line
  with constant speed.

Newtons Laws of Motion
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Inertia and Mass
2.1 Combining Forces

• Mass is the amount of matter in an object.

• The more mass an object has, the more inertia it
  has and the harder it is to change its motion.
• A bicycle is easier to push than a car because it
  has less mass.

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Lesson 1 Review
2.1 Combining Forces
Which of the following changes occur when an
unbalanced force acts on an object? A motion B mas
s C inertia D weight
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Lesson 1 Review
2.1 Combining Forces
What is the net force acting on a door if one
person pushes to the right with a force of 2000 N
and a second person pushes with a force of 1500 N
to the right? A 3500 N to the right B 3500 N to
the left C 500 N to the left D 500 N to the right
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Lesson 1 Review
2.1 Combining Forces
You are riding a bike. In which of the following
situations are the forces acting on the bike
balanced? A You pedal to speed up. B You turn at
constant speed. C You coast to slow down. D You
pedal at constant speed.
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Balanced Unbalanced Forces

• Balanced Skateboard Forces
• Draw the skateboard and the vectors in each
  direction to cause balanced forces.

• Unbalanced Skateboard Forces
• Draw the skateboard and the vectors in each
  direction to cause unbalanced forces.

• Unbalanced Frisbee Forces
• Draw the frisbee and the vectors in each
  direction to cause unbalanced forces.

• Balanced Frisbee Forces
• Draw the frisbee and the vectors in each
  direction to cause balanced forces.