Forces Motion What is a Force Force push

Forces & Motion

What is a Force? • Force: push or pull • Unit: Newton (N) Kg x m/s 2 • Vector: has both magnitude & direction

Combining Forces • Use vector addition • Net Force: the total force acting on an object • Balanced Forces: when the net force is zero ▫ No motion occurs • Unbalanced Forces: when the net force is not zero ▫ Motion occurs (acceleration or change in direction)

Balanced Forces:

Unbalanced Forces:

Friction • Friction: a force that opposes (acts opposite to) motion • Four types: ▫ ▫ Static Sliding Rolling Fluid

Types of Friction • Static: friction force on objects that are not moving (greatest friction force) • Sliding: friction force on an object as it slides over another • Rolling: friction force on an object as it rolls over another (ex. Ball bearings) • Fluid: friction force on an object in a fluid (liquid or gas) (ex. Air resistance)

Gravity • Gravity: downward force pulling objects toward the center of Earth • Acceleration on Earth due to gravity = 9. 8 m/s 2 • Terminal velocity: constant velocity that a falling object reaches when the force of gravity is equal to the air resistance

Projectile Motion • An object thrown forward will follow a curved path due to gravity • The combination of an initial forward velocity and the downward vertical force of gravity causes the object to follow a curved path

Projectile Motion

Scientists who contributed to the ideas about Force & Motion • Aristotle: incorrectly proposed that force is required to keep an object moving at a constant speed • Galileo: studied constant acceleration due to gravity • Newton: defined force & mass; introduced 3 laws of motion

Newton’s First Law of Motion • Law of Inertia • An object at rest will remain at rest and an object in motion will remain in motion unless acted upon by an outside force • If the net force = 0, then the object’s state motion will remain unchanged

Newton’s Second Law of Motion • The force acting on an object is equal to the mass of the object times the object’s acceleration • Force = mass x acceleration (or F = m x a) • Units: N = kg x m/s 2

Weight & Mass • Weight: the force of gravity acting on an object W = m x g same equation as F = m x a Changes depending on the gravitational force • Mass: a measure of inertia on an object (how much matter is within an object) Constant no matter what the gravity

Newton’s Third Law of Motion • For every action there is an equal and opposite reaction ▫ Forces occur in pairs • Not all forces create motion

Momentum • The product of an objects mass times its velocity ▫ An object with large momentum is hard to stop • Momentum = mass x velocity ▫ M=mxv ▫ Units kg*m/s = kg x m/s

Momentum

Law of Conservation of Momentum • In a closed system, the loss of momentum of one object equals the gain in momentum of another object ▫ Momentum is conserved

Universal Forces • Electromagnetic Forces: forces associated with charged particles (electric & magnetic) • Nuclear Forces: forces that occur within the nucleus of an atom • Gravitational Forces: an attractive force between any two masses

Newton’s Law of Universal Gravitation • Every object in the universe attracts every other object ▫ Closer distance = greater force ▫ Larger mass = greater force