Newton’s Laws of Motion

Newton’s Laws of Motion AP Physics Unit 2 Section 1 Newton’s Laws Lesson 1

Do Now:What is the acceleration on a F-150 (mass = 1500.0 Kg) if it starts from rest and reaches 25.0 m/s {about 55 mph} in 6.50 seconds? What is the “Force” needed to attain this acceleration? • Objectives: • 1st Law: Inertia • 2nd Law: F = ma • 3rd Law: Equal and Opposite • Homework: • TBA

Isaac Newton • Born 1642 • Went to University of Cambridge in England as a student and taught there as a professor after • Never married • Gave his attention mostly to physics and mathematics, but he also gave his attention to religion and alchemy • Newton was the first to solve three mysteries that intrigued the scientists • Laws of Motion • Laws of Planetary Orbits • Calculus

Three Laws of Motion • Newton’s Laws of Motion are laws discovered by Physicist and mathematician, Isaac Newton, that explains the objects’ motions depending on forces acted on them • Newton’s First Law: Law of Inertia • Newton’s Second Law: Law of Resultant Force • Newton’s Third Law: Law of Reciprocal Action

Newton’s First Law: InertiaNO “net” acceleration • An Object at rest remains at rest, and an object in motion continues in motion with constant velocity (that is, constant speed in a straight line), unless it experiences a net external force. • The tendency to resist change in motion is called inertia • People believed that all moving objects would eventually stop before Newton came up with his laws

Newton’s First Law • When there is no force exerted on an object, the motion of the object remains the same like described in the diagram • Because the equation of Force is F=ma, the acceleration is 0m/s². So the equation is 0N=m*0m/s² • Therefore, force is not needed to keep the object in motion, when • The object is in equilibrium when it does not change its state of motion

Newton’s Second Law:Force“net” acceleration • The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass • anet = Fnet / mass • or • F = ma Fnet Acceleration

Force • Two types of forces • Contact force • Force caused by physical contact • Field force • Force caused by gravitationalattraction between two objects • Force caused by electromagneticattraction between two objects

Friction • A force that causes resistance to motion • Arises from contact between two surfaces • If the force applied is smaller than the friction, then the object will not move • If the object is not moving, then ffriction=Fapplied • The object eventually slips when the applied force is big enough

Friction • Friction was discovered by Galileo Galilee when he rolled a ball down a slope and observed that the ball rolls up the opposite slope to about the same height, and concluded that the difference between the initial height and the final height is caused by friction. • Galileo also noticed that the ball would roll almost forever on a flat surface so that the ball can elevate to the same height as where it started.

Static Friction Friction that exists while the object is stationary If the applied force on an object becomes greater than the maximum of static friction, then the object starts moving fstatic≤μstaticn Kinetic Friction The friction that exists when an object is in motion F-fkinetic produces acceleration to the direction the object is moving If F=fkinetic, then the object moves at constant speed with no acceleration fkinetic= μkineticn Kinetic friction and the coefficient of kinetic friction are smaller than static friction and the static coefficient Two types of Friction

The car is traveling rightward and crashes into a brick wall. The brick wall acts as an unbalanced force and stops the car.

The truck stops when it crashes into the red car. But the ladder falls in front of the truck because the ladder was in motion with the truck but there is nothing stopping the ladder when the truck stops.

Unbalanced Force and Acceleration • Force is equal to acceleration multiplied by mass • When an unbalanced force acts on an object, there is always an acceleration • Acceleration differs depending on the net force • The acceleration is inversely related to the mass of the object

Net Force • Force is a vector • Because it is a vector, the net force can be determined by subtracting the force that resists motion from the force applied to the object. • If the force is applied at an angle, then trigonometry is used to find the force Fnet

R R θ θ R*sin θ R*cos θ

Gravitational Force • The force that exerts all objects toward the earth’s surface is called a gravitational force. • The magnitude of the gravitational force is called weight • The acceleration due to gravity is different in each location, but 9.80m/s² is most commonly used • Calculated with formula w=mg

Newton’s Third Law • If two objects interact, the force exerted on object 1 by object 2 is equal in magnitude but opposite in direction to the force exerted on object 2 by object 1 • Forces always come in pair when two objects interact • The forces are equal, but opposite in direction Fn Fg

Newton’s Third Law As the man jumps off the boat, he exerts the force on the boat and the boat exerts the reaction force on the man. The man leaps forward onto the pier, while the boat moves away from the pier.

Force exerted by the road Force exerted by the wheels Newton’s Third Law

Newton’s Third Law Flow pushed backward Foil deflected down

Works Cited • Henderson, Tom. Physics. Course home page. 16 May 2008 http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/newtlaws/newtltoc.html>. • Serway, Raymond A., and Jerry S. Faughn. "The Laws of Motion." College Physics . Fifth ed. 1999. • Benson, Tom. Newton’s Third Law applied to Aerodynamics 21 May 2008 http://www.grc.nasa.gov/WWW/K-12/airplane/newton3.html • Introduction to Rocket Performance. Newton’s Third Law. 12 March 2004 http://www.allstar.fiu.edu/aero/rocket1a.htm • Stern, David P. (16) Newton’s Laws of Physics. 1. Force and Inertia. 9 October 2004 http://www-istp.gsfc.nasa.gov/stargaze/Snewton.htm

Newton’s Laws of Motion