Unbalanced forces occur when the net force acting on an object is not zero. In the scenarios you provided:
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Two people stand on the same side of a large tire: one person pushes the tire and the other pulls the tire with equal force.
- This results in unbalanced forces because the forces act in different directions (one push, one pull). The net force is the difference of the two forces.
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Two people stand on the opposite sides of a tire: both people push the tire with equal force.
- This results in balanced forces because both forces are equal in magnitude and act in opposite directions, leading to a net force of zero.
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Two people stand on opposite sides of a large tire: both people pull the tire with equal force.
- This also results in balanced forces for the same reason as above; the forces are equal and opposite, resulting in a net force of zero.
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Two people stand on the same side of the large tire: both people pull the tire with equal force.
- This creates unbalanced forces. Both people are pulling in the same direction, adding to the total force, resulting in a net force greater than zero.
Therefore, the first and the fourth situations involve unbalanced forces acting upon the tire.