Chapter 12 Forces and Motion Physical Science Chapter 12 Forces and Motion

Forces and Motion What is a Force? A Force is a Push or Pull Exerted on an Object. Forces cause Objects to Speed up, Slow down, or Change Direction as they Move. A Force Exerted on an Object Causes that Object’s Velocity to Change; that is, All Forces Cause an Acceleration

Forces and Motion How can you cause an object to move? Push on it or pull on it. Push harder on an object and you have a greater effect on its motion. If you push the book to the right, the book moves towards right.

Forces and Motion Force is a Vector The Final Force is the Net (Sum) of the Total Forces on an Object If the Final Force on an Object DOES NOT = 0, the Object Is Accelerating

Forces and Motion Combining Forces Forces are Vectors They May Strengthen Each Other They May Cancel All or Part of Each Other They Are Cumulative

Units Forces are measured in units known as Newtons =N

Forces and Motion Example Problem Two horizontal forces of 225N and 165N are exerted in the same direction on a crate. What is the net force on the crate?

Forces and Motion Solution 225N 165N

Forces and Motion Solution 390N

Forces and Motion Example Problem If the same two horizontal forces of 225N and 165N are exerted in opposite directions on the crate. What is the net force on the crate?

Forces and Motion Solution 225N 165N

Forces and Motion Solution 60N

Forces and Motion Types of Forces Friction (Ff or f ) Normal (FN) Opposes Horizontal Motion Parallel to Surface Normal (FN) Exerted by Surface on the Object Perpendicular to Surface

Forces and Motion Types of Forces Tension (FT) Weight (Fg) Pull or Push Exerted by Secondary Object Parallel to Secondary Object Weight (Fg) Long Range Force Exerted by Gravity on the Object Toward the Center of the Earth

Forces and Motion Free Body Diagrams Illustrate All Forces Acting on an Object

Forces and Motion Combining Forces

Forces and Motion Friction Types Static Friction (fs) (Before motion) Kinetic friction (fk)(After motion) Rolling Friction Reduced Area of Contact Fluid Friction Drag (fdrag)

Forces and Motion Earth’s Gravity Force Pulling all Objects Toward the Center of the Earth g is the acceleration of Gravity (-9.8 m/s2) Galileo Galilei (1564-1642)

Newton’s Laws of Motion 1

Forces and Motion Newton’s First Law of Motion “Every Body Continues In Its State of Rest, Or of Uniform Motion In A Straight Line, Unless It is Compelled to Change That State by Forces Impressed Upon It.”

Forces and Motion Newton’s First Law of Motion “Every Body Continues In Its State of Rest, Or of Uniform Motion In A Straight Line, Unless It is Compelled to Change That State by Forces Impressed Upon It.” aka “The Law of Inertia”

Forces and Motion Inertia Equilibrium The Tendency of an Object to Resist a Change in Movement Equilibrium Net Force = 0

Newton’s Laws of Motion 2

Forces and Motion Newton’s Second Law of Motion “The Acceleration of a Body is Directly Proportional to the Net Force Acting on the Body and Inversely Proportional to the Mass of the Body.”

Forces and Motion Newton’s Second Law of Motion The Greater the Force on the Object, the Greater the Acceleration of the Object The Greater the Mass of the Object, the Weaker the Acceleration of the Object

Forces and Motion Newton’s Second Law of Motion Force is Related to… The Mass of the Object (m) The Acceleration of the Object (a)

Forces and Motion Measurement of Force SI Units Mass - Kilogram (kg) Distance - Meter (m) Time - Second (s)

Forces and Motion Measurement of Force The Newton (N) One Newton can accelerate 1 kg to 1 m/s2 N = 1 kg*m/s2

Forces and Motion Weight The Force of the Acceleration of Gravity on the Mass of an Object

Newton’s Laws of Motion 3

Forces and Motion Interaction Forces Newton’s Third Law of Motion “When an Object Exerts a Force On a Second Object, That Second Object Exerts an Equal and Opposite Force On the First Object.”

Forces and Motion Interaction Forces Newton’s Third Law of Motion “For Every Action There is an Equal and Opposite Reaction”

Forces and Motion Momentum Product of an Object’s Mass and Its Velocity Large Mass/ Low Velocity = Small Mass/ High Velocity

Inelastic collisions M1V1=M2V2 Example A 4.5-kg ham is thrown into a stationary 15-kg shopping cart. At what speed will the cart travel if the ham had an initial speed of 2.2 m/s?

Forces and Motion Universal Forces Electromagnetic Electric Magnetism Attract and Repel Electric Opposites Attract (Charged Particles) Magnetism Opposites Attract (Polarized Metal Molecules) Nuclear Strong and Weak in Nucleus of Atom Gravity

Forces and Motion Gravity Every Object in the Universe Attracts Every Other Object Force Relative to the Inverse of the Distance Proportional to Mass Acts over Great Distances

Forces and Motion Orbits Orbits are Maintained by the Velocity of the Object Perpendicular to Gravity Centripetal Force

Forces and Motion Homework