You were kidnapped and knocked out. Some time later, you wake up in a dark warehouse. All there is in the room is a scale and a light, so you decide to weigh yourself. WOW!!! You gained a whole lot of weight last nightwhat happened? You remember seeing alien figures in a dream-state, and realize you must be on another planet. Is the planet smaller or more massive than Earth? WARMUP SEPT 17 TH - THINK WEIGHT AND MASS Fg = mg (formula for weight) Fg (weight) is the force an object has due to gravity Gravity on the Earth 9.8m/s 2 WEIGHT AND MASS Whats the mass of my 893N ex-husband that just happens to be in my basement? WEIGHT PROBLEMS! F G =MG What does a 60kg tool weigh? Whats the mass of a crate of tools that weighs 234 N? WEIGHT AND MASS: What does a case of the new Chipotle Gatorade with a mass of 54.8kg weigh? WHAT WOULD A 60KG TOOL WEIGH: On Mars (accel of gravity 3.7m/s 2 )? On Jupiter (accel of gravity 24.8m/s 2 )? WHAT PLANET ARE YOU ON? YOU HAVE A 4KG CAT THAT WEIGHS 14.4N Planet Gravity : (m/s 2 ) a= Mercury3.61 Venus8.83 Earth9.8 Earth's Moon1.6 Mars3.75 Jupiter26 Jupiter's Moon Io1.81 Saturn11.2 Uranus10.5 Neptune13.3 Pluto0.61 NOW ITS TIME FOR NEWTONS 2 ND LAW Newtons 1 st : Inertia. At rest, stay at rest; in motion, stay in motion. Newtons 2 nd : What happens when a force acts on an object? Acceleration. Newtons Second Law: Force = mass x acceleration Force equals mass times acceleration. F=ma NEWTONS SECOND LAW: The acceleration of an object is directly proportional to the force applied to the object, and inversely proportional to the mass. -or if F then A if M then A CALCULATE THE FORCE HOW DO WE? HOW? LIKE THIS: My 4 kg cat, Jeter, ran at our kitten Shadow with an acceleration of 3.0 m/s 2. He didnt stop. Poor little kitten! After suffering a mild concussion, we wondered.how much force did Jeter hit him with? Force = mass x acceleration, or 4 x 3 = 12 12 WHAT? Remember Force has its own special unit 1kg x 1m/s 2 = 1 newton (1N) F = ma Learn it. Live it. Love it. FORCE = MASS(ACCELERATION) 1. How much force is needed to push a lawnmower of 30 kg at 2.5 m/s 2 ? 2. How much force must be applied to a bowling ball that has a mass of 5kg to achieve an acceleration of 25m/s 2 ? 3. What is the mass of a baseball that has an acceleration of 125 m/s 2 after a force of 44 Newtons has hit it? 4. What is the acceleration of a 22kg wolf that hits attacks a bear with a force of 400 Newtons? NOW YOU PRACTICE! WITHOUT FRICTION Friction - a force that opposes motion, or pushes back when two surfaces are touching. Its always around and it affects everything. WITHOUT FRICTION FRICTION- WORKS AGAINST YOU ..BUT IT CAN BE HELPFUL! WHEN DO I WANT A lot of friction? A lot of friction? A little bit of friction? A little bit of friction? FRICTION TYPES AND PARTS There are three Basic Types of Friction Static Kinetic Fluid TYPES OF FRICTION: 1) Static friction: Friction that resists the start of sliding motion between two objects at rest. Keeps things stopped TYPES OF FRICTION: 2) Kinetic friction: The force that opposes the movement of two surfaces that are in contact and moving over each other. To make something move, you just overcome static friction by pulling with a force larger than kinetic friction. KINETIC FRICTION: Sliding or Rolling TYPES OF FRICTION: 3) Fluid friction: The friction between layers of a fluid. 2 types- Liquid and Gas Liquid- water, oil etc. Gas - Air TYPES OF FRICTION: Described by viscosity. Viscosity the thickness of a fluid. Low viscosity = thin; High viscosity = thick or viscous. The less viscous a fluid is, the easier it moves. Friction DOES depend upon: 1. surface area in contact 2. mass/gravity (weight) of object 3. the texture of the surface FRICTION IS CUMULATIVE Small amounts of friction in a system add up to become a large amount of friction. TEXTBOOK FRICTIONCHALLENGE