Unit 1, Chapter 3 Integrated Science

Unit One: Forces and Motion 3.1 Force, Mass and Acceleration 3.2 Weight, Gravity and Friction 3.3 Equilibrium, Action and Reaction Chapter 3 Forces and Motion

3.1 Force, Mass and Acceleration Unless you apply force, things tend to keep on doing what they were doing in the first place. Force causes an object to accelerate, while the object’s mass resists acceleration. For every action, there is an equal and opposite reaction.

Force Every object continues in a state of rest, or motion, unless force is applied to change things. Force is an action that has the ability to change motion (Push or Pull) Commonly used units: Pounds and Newtons 1 newton = pounds 1 pound = newtons

Force is a push or pulling action that can change motion, whereas mass is the amount of “stuff” or matter in an object Weight is the force acting upon an object due to the influence of gravity On the moon… your mass would be the same but your weight would be different. WEIGHT IS A MEASURE OF FORCE… MASS IS NOT Difference between force and mass

Mass and Inertia Inertia: Property of an object to resist changing its state of motion Newton’s first law of motion is also known as the law of inertia The amount of inertia an object has depends on its mass Mass is a measure of the inertia of an object Greater mass = Greater inertia

3.1 Newton's Second Law a = F m force (newtons, N) mass (kg) acceleration (m/sec 2 ) The acceleration of an object is directly proportional to the force acting on it, and inversely proportional to its mass Force causes acceleration Mass resists acceleration

B Balanced and unbalanced forces The motion of an object depends on the total of all forces action on the object. We call the total of all forces the net force When forces on an object are balanced, the net force is zero and we say that the object is at equilibrium.

3.1 Force, Mass, and Acceleration Key Question: What is the relationship between force, mass and acceleration? *Read text section 3.1 BEFORE Investigation 3.1

3.2 Gravity What is gravity? — Gravity is a force. — Gravity depends on mass. — Gravity accelerates objects. Gravity on earth accelerates at a rate of 9.8 m/s 2

3.2 Gravity If you were on Mars, your force/mass balance would have to be adjusted. The planet is smaller than Earth and therefore Mars’s gravity is weaker.

Weight vs. Mass Weight is the force created by gravity on objects Your mass is constant throughout the universe, but your weight changes depending on what planet you are on.

3.2 Weight F w = mg gravity (9.8 m/sec 2 ) mass (kg) Weight force (N) If you know the mass of an object, you can calculate its weight using Newton’s second law

3.2 Weight and Galileo A legend has it that, around 1587, Galileo dropped two balls from the Leaning Tower of Pisa to see which would fall faster.

Weight and Mass We tend to use mass and weight interchangeably in our everyday lives BUT… in physics… Weight is never measured in grams and mass is never measured in pounds or newtons.

3.2 Gravity The attractive force from gravity between objects of ordinary mass is incredibly small.

3.2 Gravity You feel weight because the mass of Earth is large enough to create significant gravity forces.

3.2 Newton's Law of Universal Gravitation The force of attraction between two objects is directly related to the masses of the objects and inversely related to the square of the distance between them.

3.2 Newton's Law of Universal Gravitation F = G m 1 m 2 R 2 gravity (9.8 m/sec 2 ) mass 1 (kg) Force (N) mass 2 (kg) distance (m) between m 1 and m 2

3.2 Weight, Gravity and Friction Key Question: How does increasing the mass of the car affect its acceleration? *Read text section 3.2 BEFORE Investigation 3.2

3.2 Friction Friction is a force that always opposes motion. What is left is often called the net force. What is the net force acting on the car? Friction reduces acceleration

Types of Friction Air Friction : air around moving objects creates opposing friction Sliding Friction : when two surfaces rub against each other Viscous Friction: Objects that move in liquids Rolling Friction: One object rolling over another Objects that continuously rub against each other will cause wear

3.3 Equilibrium, Action and Reaction Key Question: What is Newton's third law of motion? *Read text section 3.3 AFTER Investigation 3.3

Momentum — explains why the speed and the direction of motion are related to the mass of the object 3.3 Equilibrium, Action and Reaction

3.3 Momentum P = mv velocity (m/sec) mass (kg) Momentum (kg-m/sec) Law of Conservation of Momentum: As long as interacting objects are not influenced by outside forces, their momentum before the interaction will equal their momentum after the interaction.