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What is a force?

What is a force?. Pick up 2 sheets in the back. Watch the book What am I doing in all of these demonstrations? I am applying a force Definition of FORCE Any push or pull that causes an object to change its current state of motion or shape. Can forces be seen?

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What is a force?

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  1. What is a force? Pick up 2 sheets in the back

  2. Watch the book • What am I doing in all of these demonstrations? • I am applying a force • Definition of FORCE • Any push or pull that causes an object to change its current state of motion or shape

  3. Can forces be seen? • No– only the result of the application of the force can be seen. • Watch the ball: • You can’t see the force I apply to the ball. • You can only see the result of the force • the ball moves

  4. What is the unit of force? • A Newton- named after Sir Isaac Newton • Abbreviation – capital N • What does it mean? • A force of 1 N gives an acceleration of 1 m/s/s to a 1kg mass.

  5. Forces can be used to change the state of motion of an object or change the shape of the object. • Can start objects moving • Can stop moving objects • Can change the direction of an object’s motion • Can change the shape of an object • Crumpling a piece of paper Forces can result in ACCELERATIONS

  6. Sometimes you can exert a force on an object and no change in motion or shape occurs. • These types of forces are called. • balanced forces • Definition of balanced force: • A force that produces no change. • A force that has an equal and opposing force. • Equal in size and opposite in direction

  7. Example: A person sitting in a chair. (Force arrow diagram) 100 N 100 N

  8. Arrows symbolize forces. These arrows have both size (scientists call it magnitude) and direction. Therefore, force is a vector quantity. • The forces we spoke of earlier, the ones that changed the state of motion of an object or the shape of the object are called UNBALANCED FORCES. This is the type of force needed to produce motion.

  9. Example : A person who breaks a chair by sitting on it.

  10. Unbalanced forces produce a net force. A net force causes a change in the current state of motion of an object. It can also cause the shape of an object to change. • Example: Tug of war (Force arrow diagram) Net force = 5 N to the left

  11. Before we go any further we need to talk about types of forces. There are many types of forces but we will only touch on seven in detail. There are two others I’d like to mention: • Nuclear force: The strong nuclear force is the force that holds the protons and neutrons together in the nucleus of atoms. • Molecular force: The attraction of molecules for each other results in two kinds of forces. • Cohesion-force of attraction between like molecules (ever do a belly flop?) • Adhesion-force of attraction between unlike molecules (tape, glue-adhesives)

  12. Applied Force

  13. Gravity Force “weight”

  14. Normal Force Balanced forces- no change in current state of motion

  15. Frictional Force • Friction opposes motion • Must be contact between two surfaces

  16. Air Resistance • Unbalanced forces • object accelerates

  17. Air Resistance #2 • Piece of paper falling to the ground • Balanced forces • Object falls at a constant speed

  18. Tensional Force Teachers Win!

  19. Spring Force • Mass hanging on spring • Stretched spring • Spring wants to return to rest position

  20. Spring Force #2 • Compressed Spring • Spring wants to return to rest position

  21. Free Body Diagrams Divide the front side into 6 equal boxes • Divide the back into 4 boxes • Create the 10 diagrams for homework. • Follow the directions • Read the descriptions carefully.

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