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==Key Stage 4==
===Meaning===
'''Newton's First Law''' states that "An [[object]] in motion will tend to stay in motion and an [[object]] at rest will tend to stay at rest unless an [[Unbalanced ForceForces|unbalanced force]] acts upon it."
===About Newton's First Law===
:: If the [[Resultant Force|resultant force]] on an [[object]] is zero then it will continue to move at a constant [[velocity]].
:: If the [[Resultant Force|resultant force]] on an [[object]] is not [[zero]] then an [[object]] will [[accelerate]] (change speed or direction).
: This means that if an [[object]] is [[observe]]d changing [[speed]] or direction then there must be an [[Unbalanced ForceForces|unbalanced force]] acting on it.