Newton's Laws of Motion Isaac Newton (17th century scientist)

Sir Isaac Newton Lived from 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 like inventing calculus and reflecting telescopes – all while college was cancelled because of the bubonic plague.

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 NewtonsYour weight in Newtons!!!

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 than on Earth. Weight on other worlds

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?

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.

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. Solving Problems

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= Fforce 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.

Concept Check: Why does a tractor trailer have a bigger engine than a car? Why would a truck driver want to leave more space between the car in front of it than a normal car?

Concept Check: Explain the net force in each graph

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)

Videos Football and HockeyFootballHockey Newtons Three Laws

6.3 Collisions Newton’s third law tells us that any time two objects hit each other, they exert equal and opposite forces on each other. The effect of the force is not always the same.

6.3 Momentum Momentum is the mass of an object times its velocity. The units for momentum are kilogram-meter per second (kg·m/s).

6.3 Momentum The law of conservation of momentum states that as long as the interacting objects are not influenced by outside forces (like friction) the total amount of momentum is constant or does not change. P before =P after m 1 v 1 = m 2 v 2

6.3 Momentum The result of a skateboarder throwing a 1-kg ball at a speed of - 20 m/sec is that he and the skateboard with a total mass of 40 kg move backward at a speed of +0.5 m/sec (if you ignore friction). We use positive and negative numbers to show opposite directions.

6.3 Collisions Elastic collisions – objects bounce and continue with full momentum Inelastic collisions – objects deform and/or join. Momentum is transferred to other energy. When a large truck hits a small car, the forces are equal. The small car experiences a much greater change in velocity much more rapidly than the big truck. Which vehicle ends up with more damage?

Solving Problems If an astronaut in space were to release a 2- kilogram wrench at a speed of 10 m/s, the astronaut would move backward at what speed? The astronaut’s mass is 100 kilograms.