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Page 1: What is a force?

What is a force?What is a force?

Pick up 2 sheets in the backPick up 2 sheets in the back

Page 2: What is a force?

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

Page 3: What is a force?

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

Page 4: What is a force?

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.

Page 5: What is a force?

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

Page 6: What is a force?

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

Page 7: What is a force?

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

100 N

100 N

Page 8: What is a force?

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.

Page 9: What is a force?

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

Page 10: What is a force?

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

Page 11: What is a force?

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)

Page 12: What is a force?

Applied ForceApplied Force

Page 13: What is a force?

Gravity Force “weight”Gravity Force “weight”

Page 14: What is a force?

Normal ForceNormal Force

Balanced forces- no change in current state of motion

Page 15: What is a force?

Frictional ForceFrictional Force

•Friction opposes motion

•Must be contact between two surfaces

Page 16: What is a force?

Air ResistanceAir Resistance

•Unbalanced forces•object accelerates

Page 17: What is a force?

Air Resistance #2Air Resistance #2•Piece of paper falling to the ground

•Balanced forces

•Object falls at a constant speed

Page 18: What is a force?
Page 19: What is a force?

Tensional ForceTensional Force

Teachers Win!

Page 20: What is a force?

Spring ForceSpring Force

•Mass hanging on spring

•Stretched spring

•Spring wants to return to rest position

Page 21: What is a force?

Spring Force #2Spring Force #2

•Compressed Spring

•Spring wants to return to rest position

Page 22: What is a force?

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


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