Forces Chapter 3

Force, Mass, & Acceleration More force on an object = more acceleration The acceleration of an object depends on its mass as well as the force exerted on it. Ex: thrown softball vs baseball

Newton’s 2nd Law of Motion The acceleration of an object is in the same direction as the net force on the object Force is Measured in Newtons Equation: Acceleration = (net)force/mass or a = f(net)/m = m/s To find force: f = ma To find mass: m = f/a

Friction A force that opposes the motion of objects that touch or between 2 objects in contact Air resistance: friction acting on objects moving through the air Objects with larger surface areas = greater air resistance Also affected by size, shape, and speed

3 Main Types of Friction 1.) Static Friction: force that prevents two surfaces from sliding past each other.(Box across the floor) 2.) Sliding: forces that are caused by an object as it slides over a surface 3.) Rolling: friction force that acts on rolling objects

Air Resistance Type of fluid friction Falling, running, … More surface exposed = more resistance Ex: flying squirrel, skydiving

High Resist

High Resist

Low Resist

Low Resist

Gravity Force that acts between any two masses The greater the mass, the larger the gravitational force The closer the objects, the larger the attraction Acceleration due to Gravity = 9.8 m/s2

Gravity Factors Size/Mass Distance Bigger = more gravity Ex: Jupiter, Earth, Moon Distance Farther = weaker

Gravity Free fall: Projectile Motion: the motion of an object when only the force of gravity is acting on it Projectile Motion: The motion of a falling object after it is given initial forward velocity Follows a curved path due to initial velocity and force of gravity

Weight and Mass Weight: the force of gravity acting on an object Weight = Mass X Free-fall acceleration or w = mg (g = 9.8 m/s2) Mass: measure of the inertia of an object; more mass = more inertia and weight

Gravity/Air Resist Gravity pulls down Air Resist. pushes up Terminal Velocity = constant velocity when air resist is same as gravity can’t go any faster

Mass & Weight Mass Weight Amount of matter Doesn’t change Balance Unit = grams Force of gravity Changes (moon) Scale Unit = Newtons (N), Pounds (lb)

Earth’s Gravitational Acceleration Equation: Force of Gravity = Mass x accelaeration

Weight Weight = mass . gravity W = m . g Units: W = N, m = kg, g = 9.8 m/s2

Projectile & Gravity 2 objects dropped @ same time (no air resist) – will hit at same time Even projectile & dropped object hit same time Gravity only force pulling down

Centripetal Force Acceleration toward the center of a curved path. Ex: The swings at a carnival Swinging a bucket at the end of a string.

12.3 Newton’s 3rd Law of Motion Whenever one object exerts a force on a second object, the 2nd object exerts an equal and opposite force on the 1st Action – Reaction Force The action/reaction force occurs at the same time; for every action, there is an equal and opposite reaction

Momentum The product of the objects mass and its velocity The larger the mass, the more momentum Equation: Momentum = mass X velocity Or: p = mv

Law of Conservation of Momentum If no net force acts on a system, then the total momentum of the system does not change In a closed system, the loss of momentum of one object equals the gain in momentum of another object