# Newton’s First Law of Motion (Inertia) “An object at rest remains at rest, and an object in motion continues in motion with a constant velocity unless.

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Newton’s First Law of Motion (Inertia) “An object at rest remains at rest, and an object in motion continues in motion with a constant velocity unless the object experiences a net external force.” Inertia is the tendency of an object to maintain its state of motion.

Forces Stationary Object FxFxFxFx An applied external force (Fx) greater than an object’s natural resisting force (Fr) will cause the object to move. The forces are added together to get the net force (ΣF). Fr ΣFΣFΣFΣF

Newton’s First Law of Motion (Cont.)  Net external force is total force resulting from a combination of external forces on an object.  When there is no change in motion, an object is said to be at equilibrium.

Example Problem: Four forces act on a hot-air balloon (shown below). Find the magnitude and direction of the resultant force on the balloon. 5120 5120 N 4050 N 1520 N 950 N ∑ F in X direction 1520 N – 950 N = 570 N Left ∑ F in Y direction 5120 N – 4050 N = 1070 N Up θ 570 N 1070 N F F ² = (1070 N) ² + (570) ² F= 1212 N θ = Tan ־ ¹ (1070 N / 570 N) θ = 62° up from the horizontal

Newton’ First Law of Motion (Cont.) - Mass is also a measurement of inertia. - The greater the mass of an object, the less it accelerates under an applied force. Therefore the greater mass has the greater inertia. F Forward

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