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Download Unit 4.1 Newton`s Laws Objectives Force
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Transcript
Unit 4.1 Newton’s Laws Teacher: Dr. Van Der Sluys Objectives • • • • • Force Inertia Mass Weight Newton’s Laws of Motion Force • Any kind of push or pull represents a force. • Applying a net force to an object will cause the object to accelerate • If there are equal forces in opposite directions the object will not accelerate (velocity is either 0 m/s or a constant) 1 Inertia • Inertia is the tendency of a object to not change position or to have a constant velocity. • A force must be applied to change the inertia of an object. Mass • Mass is a measure of the inertia of an object. • The greater the mass of an object the greater the force required to change its inertia • The SI standard unit of mass is the kilogram (kg) Weight • Weight is the force that results when an object of a particular mass is placed in a gravitation field • The unit for weight is the Newton (N) • An apple has a weight of approximately 1N 2 Sir Issac Newton http://en.wikipedia.org/ wiki/Isaac_Newton Newton’s First Law • A body at rest tends to stay at rest unless an unequal set of forces is applied • A body in motion tends to stay in motion with constant velocity unless an unequal set of forces is applied Newton’s Second Law • The acceleration (a) of an object with mass (m) is directly proportional to the net force (F) acting on the object. • The direction of the force is a vector in the same direction as the acceleration. • Force is measured in units of Newtons (N) • 1 N = 1 kg.m/s2 F = ma 3 What is the mass of an apple whose weight is 1 N? F = ma a = 9.8 m/s2 and F = 1 N 1 N = m (9.8 m/s2) 1 kg.m/s2 m = 9.8 m/s2 m = 0.1 kg Newton’s Third Law • When one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. • The action and reaction forces act on different objects. Describe the forces when a hammer hits a nail. • What happens to the nail? • What is the direction of the nail’s acceleration? • What happens to the hammer? • What happens to the hammer’s acceleration? 4
