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Push and Pull

Push and Pull. Newton’s Laws. Newton’s First Law. “An object at rest remains at rest, OR an object in motion stays in motion unless acted on by an unbalanced external force .”. Also known as the “ Law of Inertia ”. Inertia Tendency of an object to maintain its STATE OF MOTION

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Push and Pull

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  1. Push and Pull Newton’s Laws

  2. Newton’s First Law “An object at rest remains at rest, OR an object in motion stays in motion unless acted on by an unbalanced external force.” Also known as the “Law of Inertia” Inertia Tendency of an object tomaintain its STATE OF MOTION Proportional to MASS

  3. Do these guys have a lot of inertia? LOTS OF INERTIA hard to… GET MOVING or STOP MORE MASS means MORE INERTIA

  4. Newton’s Third Law • “For every action there is an equal and opposite reaction.” • If you push against a wall with a 5N force. How much force does the wall push on you?

  5. Third Law Examples • A firefighter directs a stream of water from a hose to the east. In what direction is the force on the hose? • A man getting out of a rowboat jumps north onto the dock. What happens to the boat? There will be a force on the hose to the WEST The boat will move to the SOUTH

  6. Newton’s Second Law “The acceleration of an object is directly proportional to the net external force acting on the object and inversely proportional to the mass of the object.” In your RT! Unit of force is theNEWTON (N)

  7. Example • A 5kg block accelerates at 2m/s2 . How much force is acting on it? • The same force acts on a 2kg block. How fast does it accelerate?

  8. Force • A push or pull on an object • Changes the STATE OF MOTIONof an object • CONTACT FORCE • Physical interaction between objects • FIELD FORCE • “Action over a distance” • Example: Gravity (Weight)

  9. Types of Forces • Normal Force • A reaction force that is always PERPENDICULAR to the surface • Tension • Force in a string that PULLS an object • Friction • A retarding force that OPPOSES MOTION • Weight • Pull from gravity • ALWAYS STRAIGHT DOWNWARD

  10. Mass ≠ Weight • MASS AND WEIGHT ARE NOT THE SAME!!! • Massis measured in kilograms(kg) • Weightis measured in Newtons(N) • However, the two ARE RELATED • Weight depends on the pull of gravity

  11. Weight • Weight is another type of force that pulls all objects straight down • Which acceleration always goes straight down? • GRAVITY

  12. A block of wood is sitting motionless on a table. Which forces are acting on it? Normal FN Weight Fg

  13. SIDE NOTE: When an object is on a flat level surface; FN = Fg Tension FT FN Fg Fg

  14. Physics Phrases • “MOTIONLESS” OR • “MOVING WITH CONSTANT VELOCITY” • ACCELERATION = ZERO • Therefore the FORCE = ZERO

  15. Physics Phrases • If there is an UNBALANCED FORCE, then the object is ACCELERATING • If the object is ACCELERATING, then there is a FORCE acting on the object • Force and Acceleration are directly related • If you have one, then you have the other!

  16. Force  Acceleration • How much acceleration? • Depends on: • AMOUNT OF FORCE • MORE FORCE = MORE ACCELERATION • MASS OF OBJECT • MORE MASS = LESS ACCELERATION

  17. Example • A glass bottle with a mass of 10 kilograms is sitting on a counter. • Calculate the bottle’s weight • Calculate the force the countertop exert on the bottle If motionless, then FN = Fg FN = 98.1 N

  18. SUMMARY • Define Newton’s 1st Law • Mass is directly proportional to… • Define Newton’s 2nd Law • Equation? • Define a Force • Units? • List and Describe the forces we will mainly see • Define Newton’s 3rd Law • Which state(s) can an object be in when the sum of all the forces equal zero?

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