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Transcript
Newton's Laws of Motion Isaac Newton (17th century scientist) Sir Isaac Newton • Lived from 1642-1727 in England. • He was a dedicated physicist and mathematician, and is considered to be one of the most brilliant scientists of all time. • He is most famous for his three laws of motion and his universal law of gravitation, but did much more. Mass & Weight • Mass is the amount of “stuff” or matter that an object contains. • Weight and Mass are different. • Weight, or how much an object weighs, depends on the amount of gravity acting upon it. – Ex. You weigh less on the moon then on Earth. Weight on other worlds Force • A force is what we call a push or a pull, or any action that has the ability to change motion of an object. • The metric unit used to describe force is called the Newton (N). One Newton is equal to: 1 Kg x 1 m/s/s Thus, one Newton of force causes a one kilogram object to accelerate at a rate of one meter per second squared. Your weight in Newtons!!! Balanced and Unbalanced Forces • The motion of all objects depends on the total of all forces acting on the object. • We call the total of all forces the net force. • Reminder – add forces acting in same direction, subtract, when in opposite direction Balanced and Unbalanced Forces Newton’s First Law of Motion • An object at rest will remain at rest, and an object in motion will remain in motion unless acted upon by an unbalanced force. • Unbalanced forces cause acceleration. – When you roll a ball, why doesn’t it roll on forever? FRICTION – This concept is also referred to as the Law of Inertia The Law of Inertia Inertia • Inertia is defined as the property of an object to resist changing its state of motion. • The amount of inertia that an object has depends on the amount of mass that it has. • The more massive the object is the harder it is to move or stop. Which is easier to push? Which is easier to stop? Solving Problems A car drives along the highway at constant velocity. Find the car’s weight and the friction force if the engine produces a force of 2,000 newtons between the tires and the road and the normal force on the car is 12,000 N. Concept Check: Ben Tooclose is being chased through the woods by a massive bull moose If Ben makes a zigzag pattern through the woods, he will be able to use the large mass of the moose to his own advantage. Explain this in terms of inertia and Newton's first law of motion. Concept Check: Mr. Wegley spends most Sunday afternoons at rest on the sofa consuming large quantities of food. What effect (if any) does this practice have upon his inertia? Explain. Newton’s Second Law of Motion • Newton’s second law relates the applied force on an object, the mass of an object and the acceleration. • It states: F = M x A • Another form of this equation says: • A= ___ F force causes acceleration M mass resists acceleration Newton’s second law • There are three main ideas related to Newton’s Second Law: 1. Acceleration is the result of unbalanced forces. 2. A larger force makes a proportionally larger acceleration. 3. Acceleration is inversely proportional to mass. 1 3 2 4 Concept Check: Why would a truck driver want to leave more space between the car in front of it than a normal car? Newton’s Third Law of Motion • For every action there is an equal and opposite reaction. • If you push on something it pushes back with the exact same force. • Forces come in pairs Newton’s Third Law of Motion • Sometimes the reaction force is noticeable and causes motion – (ex – recoil from a gun, pushing off while on ice) • Sometimes it is more subtle, but forces ALWAYS act in pairs. – (ex - sitting in a chair, walking) Concept Check: Explain the net force in each graph Videos • Football and Hockey • Newtons Three Laws