What are balanced and unbalanced forces? Can you please provide an example as well.

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gsenviro eNotes educator| Certified Educator

Forces always occur in pairs. Balanced forces are those forces that are equal in magnitude and opposite in direction and hence balance each other out. An example of a pair of balanced forces is a tug of war between two equal teams (in terms of strength). In such a case, each team will exert an almost equal force, but in opposite direction and hence net force would be zero and no team will win. Balanced forces do not cause change in direction or speed. If a body at rest is acted upon a pair of balanced forces, it will continue to be at rest. For example, if you were to push down a book on top of a table, this external force would be balanced by the reaction of table on the book and hence no change in the state of motion.

Unbalanced forces are those that have different magnitude and may or may not act in opposite directions. An example is a ball rolling on the ground (as a result of a gentle shove) will ultimately stop due to ground friction. These two forces (shove and friction) opposed each other and due to different magnitude caused a change in the velocity of object. Unbalanced forces may also cause a change in direction of motion.

Hope this helps. 

elzbaker | Student

The forces acting on an object can be balanced or unbalanced. When sitting on a chair, the force of gravity pulls you downwards, towards Earth. The chair supports you by pushing upwards. This balances the downwards force of gravity.

Balanced forces don’t always mean that the object is stopped - it might be travelling at the same speed without changing directions. Consider a girl, about to ride her bike. To take off, she must accelerate, pedalling fast and hard to produce a force large enough to push her forwards. She needs to overcome the friction caused by the roughness of the road and by the air that she pushes through. To speed up, she keeps accelerating. Her pedalling needs to provide a driving force that is bigger than the force of friction acting in the opposite direction. As she continues her journey, she may travel at a constant speed without slowing down or speeding up. When this happens, the forwards force from her pedalling is cancelled out by the friction forces pushing her backwards. At this stage, her motion is constant and all of the forces acting on her are balanced.

Whenever the forces acting on the girl are unbalanced, her motion will change. Motion always changes in the direction of the unbalanced force. This means that the forces are unbalanced when she:

  • Starts moving (by pedalling fast and hard)
  • Speeds up (by pedalling faster and harder)
  • Slows down (by using the breaks)
  • Comes to a stop (by using the breaks)
  • Changes direction (by turning the handlebars)

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