what is a force?
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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? - PowerPoint PPT PresentationTRANSCRIPT
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What is a force?What is a force?
Pick up 2 sheets in the backPick up 2 sheets in the back
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Watch the bookWatch the book
What am I doing in all of these What am I doing in all of these demonstrations?demonstrations?I am applying a force
Definition of FORCEDefinition of FORCEAny push or pull that causes an
object to change its current state of motion or shape
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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 forcethe ball moves
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What is the unit of force?What is the unit of force?A Newton- named after Sir Isaac Newton
Abbreviation – capital NWhat does it mean?
A force of 1 N gives an acceleration of 1 m/s/s to a 1kg mass.
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Forces can be used to change the Forces can be used to change the state of motion of an object or change state of motion of an object or change the shape of the object. the shape of the object. Can start objects movingCan stop moving objectsCan change the direction of an object’s
motionCan change the shape of an objectCan change the shape of an object
Crumpling a piece of paperCrumpling a piece of paper
Forces can result in
ACCELERATIONS
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Sometimes you can exert a force on Sometimes you can exert a force on an object and no change in motion or an object and no change in motion or shape occurs.shape occurs.
These types of forces are called.These types of forces are called.balanced forces
Definition of balanced force: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
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Example: A person sitting in a chair. (Force arrow Example: A person sitting in a chair. (Force arrow diagram)diagram)
100 N
100 N
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Arrows symbolize forces. These arrows Arrows symbolize forces. These arrows have both size (scientists call it have both size (scientists call it magnitudemagnitude) and direction. Therefore, ) and direction. Therefore, force is a force is a vector quantityvector quantity..
The forces we spoke of earlier, the ones The forces we spoke of earlier, the ones that changed the state of motion of an that changed the state of motion of an object or the shape of the object are called object or the shape of the object are called UNBALANCED FORCES. This is the type . This is the type of force needed to produce motion. of force needed to produce motion.
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Example : A person who breaks a chair by sitting on it.Example : A person who breaks a chair by sitting on it.
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Unbalanced forces produce a Unbalanced forces produce a net forcenet force. A net force . A net force causes a change in the current state of motion of an causes a change in the current state of motion of an object. It can also cause the shape of an object to object. It can also cause the shape of an object to change.change.
Example: Tug of war (Force arrow diagram)Example: Tug of war (Force arrow diagram)
Net force = 5 N to the left
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Before we go any further we need to talk about Before we go any further we need to talk about types of forces. There are many types of forces types of forces. There are many types of forces but we will only touch on seven in detail. There but we will only touch on seven in detail. There are two others I’d like to mention:are two others I’d like to mention:
Nuclear forceNuclear force: The strong nuclear force is the : The strong nuclear force is the force that holds the protons and neutrons force that holds the protons and neutrons together in the nucleus of atoms.together in the nucleus of atoms.
Molecular forceMolecular force: The attraction of molecules : The attraction of molecules for each other results in two kinds of forces.for each other results in two kinds of forces.
CohesionCohesion-force of attraction between like -force of attraction between like molecules (ever do a belly flop?)molecules (ever do a belly flop?)
Adhesion-Adhesion-force of attraction between unlike force of attraction between unlike molecules (tape, glue-adhesives) molecules (tape, glue-adhesives)
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Applied ForceApplied Force
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Gravity Force “weight”Gravity Force “weight”
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Normal ForceNormal Force
Balanced forces- no change in current state of motion
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Frictional ForceFrictional Force
•Friction opposes motion
•Must be contact between two surfaces
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Air ResistanceAir Resistance
•Unbalanced forces•object accelerates
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Air Resistance #2Air Resistance #2•Piece of paper falling to the ground
•Balanced forces
•Object falls at a constant speed
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Tensional ForceTensional Force
Teachers Win!
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Spring ForceSpring Force
•Mass hanging on spring
•Stretched spring
•Spring wants to return to rest position
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Spring Force #2Spring Force #2
•Compressed Spring
•Spring wants to return to rest position
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Divide the front side into 6 equal boxesDivide the front side into 6 equal boxesDivide the back into 4 boxesDivide the back into 4 boxes
Create the 10 diagrams for Create the 10 diagrams for homework.homework.Follow the directionsFollow the directionsRead the descriptions carefully.Read the descriptions carefully.
Free Body DiagramsFree Body Diagrams