Forces and Motion

Describing Motion An object is in motion when its distance from a reference point is changing Variables involved?

Speed and Velocity Speed = distance ÷ time Average speed = total distance total time Velocity is speed in a certain direction

Graphing Speed

Acceleration The rate at which velocity changes  Increasing speed  Decreasing speed  Changing direction Acceleration = Change in velocity Change in time

Explaining Motion – Newton’s Laws Galileo → Isaac Newton

Force A push or pull; ex. Tug of War A transfer of energy Net Force = the sum of all forces on an object Vector diagram – magnitude and direction 1 Newton = the force required to accelerate a 1 kg mass at 1 m/sec 2

Newton’s First Law (aka The 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 unbalanced force  Inertia – resistance to change; an object’s tendency to keep doing what it’s doing What does mass have to do with inertia?

Types of Forces Friction  Force that occurs when the surfaces of matter move past each other  Always opposes motion  Produces heat  Amount of friction depends on……. Amount of force pushing objects together How rough/smooth the surfaces are

Friction Forces Sliding Rolling Fluid Static

Friction: Helpful or Harmful? Ways to increase friction Ways to decrease friction Friction animation

Gravity or The Law of Universal Gravitation Force of attraction between objects  Affected by the mass of the objects and the distance between them  Weight = measure of the gravitational force exerted on an object  Falling objects ?  Terminal velocity Terminal velocity  Freefall Freefall

Orbit Projectile Motion

Newton’s 2 nd Law The acceleration of an object depends on the mass of the object and the amount of force applied How is acceleration changed by force? How is acceleration changed by mass?

Force = Mass X Acceleration Newton = kg x m/sec 2 What is the net force on a 1000 kg elevator accelerating at 2m/sec 2 ? What is the net force required to accelerate a 55 kg shopping cart at 15 m/sec 2 ?

Newton’s 3 rd Law aka The Action/Reaction Law For every action, there is an equal and opposite reaction When one object exerts a force on a second object, the second object exerts a force of equal strength in the opposite direction  All forces act in pairs  The forces are applied to two different objects

Momentum A measure of an object’s “inertia of motion” Momentum = Mass x velocity kg·m/sec Law of Conservation of Momentum: the total momentum of objects that interact does not change, unless acted on by an outside force (eg. Friction) Collision Animations

ObjectMass (kg)Velocity (m/s)Momentum (kg·m/s) Blackbird Soccer player10010 Skier6020 Bullet Frog0.912 Meteorite0.11,000 Baseball Rocket36,0001,800 Wagon23 Satellite3,0008,000