8TH GRADE SCIENCE
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​balanced vs. Unbalanced Forces

Forces have a magnitude (strength) and a direction. Forces can be represented as arrows with the length of the arrow representing the magnitude of the force and the head of the arrow pointing in the direction of the force.  Using such arrows, the resulting force (net force) and direction can be determined.
Forces acting on an object can be balanced or unbalanced.
Picture
​Balanced forces will cause no change in the speed of an object.
  • Balanced forces acting on an object in opposite directions and equal in strength, as shown in the arrows below, do not cause a change in the speed of a moving object.
  • Objects that are not moving will not start moving if acted on by balanced forces.
For example, in arm wrestling where there is no winner, the force exerted by each person is equal, but they are pushing in opposite directions. The resulting force (net force) is zero.
  • Or, in a tug of war, if there is no movement in the rope, the two teams are exerting equal, but opposite forces that are balanced. Again, the resulting force (net force) is zero.
Picture
Picture
Unbalanced forces are not equal, and they always cause the motion of an object to change the speed and/or direction that it is moving.
  • When two unbalanced forces are exerted in opposite directions, their combined force is equal to the difference between the two forces.
  • The magnitude and direction of the net force affects the resulting motion
  • This combined force is exerted in the direction of the larger force
  • For example, if two students push on opposite sides of a box sitting on the floor, the student on the left pushes with less force (small arrow) on the box than the student on the right side of the box (long arrow).
  • The resulting action (net force: smaller arrow to the right of the = shows that the box will change its motion in the direction of the greater force as shown below:
Picture
  • Or, if in a tug of war, one team pulls harder than the other, the resulting action (net force) will be that the rope will change its motion in the direction of the force with the greater strength/magnitude as shown below:
Picture
  • If unbalanced forces are exerted in the same direction, the resulting force (net force) will be the sum of the forces in the direction the forces are applied.
    • For example, if two people pull on an object at the same time in the same direction, the applied force on the object will be the result of their combined forces (net force or longer arrow to the right of the =) as shown below:
Picture
  • When forces act in the same direction, their forces are added. When forces act in opposite directions, their forces are subtracted from each other.
  • Unbalanced forces also cause a nonmoving object to change its motion
  • If there is no net force acting on the object, the motion does not change. If there is a net force acting on an object, the speed of the object will change in the direction of the net force.
Picture

Extended Learning

  • Investigate pressure using the formula (Pressure = force/area)
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  • Home
  • Earth Systems and Resources
    • Weathering, Erosion, Deposition
    • Rock Cycle
    • Earth Layers >
      • Evidence for Earth's Layers
    • Plate Tectonics >
      • Continental Drift
      • Divergent Plate Boundaries
      • Convergent Plate Boundaries
      • Transform Plate Boundaries
      • Hot Spots
    • Evidence for Plate Tectonics
    • Patterns of Earthquakes and Volcanoes
    • Forces inside Earth
    • Catastrophic Events >
      • South Carolina Earthquakes
    • Earth Resources
  • Earth's History and Diversity of Life
    • Geologic Time >
      • Geologic Time Scale
      • Precambrian
      • Paleozoic Era
      • Mesozoic Era >
        • Explore Dinosaurs
      • Cenozoic Era
    • Law of Superposition & Index Fossils
    • Catastrophic Events
    • Fossil Evidence
    • Fossil Formation
    • Adaptations & Natural Selection
    • Extinction Factors >
      • Endangered Species
  • Earth's Place in the Universe
    • Milky Way Galaxy
    • Expanding Universe
    • Our Sun
    • The Solar System >
      • Mercury
      • Venus
      • Earth
      • Mars
      • Jupiter
      • Saturn
      • Uranus
      • Neptune
      • Solar System Exploration
    • Celestial Objects
    • Gravity
    • Seasons
    • Sun-Earth-Moon Motion
    • Phases of the Moon
    • Eclipses
    • Tides
    • Space Technology
  • Forces and Motion
    • Force vs. Mass (F=ma)
    • Balanced vs. Unbalanced Forces
    • Inertia
    • Action = Reaction
    • Friction & Gravity
    • Graphing Motion
    • Average Speed
    • Newton's Laws of Motion
  • Waves
    • Matter & Energy
    • Properties of Waves
    • Behavior of Waves
    • Interacting Waves
    • How We See in Color
    • The Electromagnetic Spectrum
    • Electromagnetic Technology
  • Engineering Design Process
  • Scientific Method(s)
  • Rocket Science!
  • Vocabulary Practice
  • State Standards & Indicators
  • Need Help?