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Aristotle 384 – 322 BC
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1564 - 1642
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1643 - 1727 ISAAC NEWTON
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An object continues in a state of rest or in a state of motion at a constant speed along a straight line, unless compelled to change that state by a net force. The net force is the vector sum of all of the forces acting on an object. Newton ’ s First Law
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Inertia is the natural tendency of an object to remain at rest in motion at a constant speed along a straight line. The mass of an object is a quantitative measure of inertia. SI Unit of Mass: kilogram (kg)
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An object is resting on a flat surface An object is being pulled on a flat surface, but is not moving
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An object is being pulled at a constant speed on a flat surface An object is being pulled with a force that is making an angle with the horizontal. The object is not moving
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An object is being pulled with a force that is making an angle with the horizontal. The object is moving with a constant velocity An object is being pulled with a force that is making an angle with the horizontal. The object is not moving
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NEWTON’S II LAW When a net external force acts on an object with mass m, the acceleration that results is directly proportional to the net force and has a magnitude that is inversely proportional to the mass. The direction of the acceleration is the same as the direction of the force.
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[NEWTON]= [N] [N] = [kg ·m/s 2 ] A net force of 1N exerted on an object with a mass of 1 kg will result in the object moving with an acceleration of 1 m/s 2
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EXAMPLE Space-shuttle astronauts experience accelerations of about 35 m/s 2 during takeoff. What force does a 75 kg astronaut experience during an acceleration of this magnitude?
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EXAMPLE A block with a mass of 5 kg is being pulled across a tabletop by a force of 10 N applied by a string tied to the front end of the block. The table exerts a 2-N frictional force on the block. What is the acceleration of the block? 2N 10 N
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EXAMPLE A 7.5 kg bowling ball initially at rest is dropped from the top of an 11m building. It hits the ground 1.5s later. Find the net external force on the falling ball.
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REDRAW FOR ACCELERATED MOTION An object is being pulled on a flat surface, and is moving with acceleration An object is being pulled with a force that is making an angle with the horizontal. The object is moving with acceleration
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