Forces and Free Forces and Free Body DiagramsBody Diagrams

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BellworkBellwork What book did Newton write in 1687?What book did Newton write in 1687? The PrincipiaThe Principia (Mathematical Principles of (Mathematical Principles of

Natural Philosophy) Natural Philosophy)

Force and Free Body DiagramsForce and Free Body Diagrams Free-body diagrams (F.B.D.):Free-body diagrams (F.B.D.): Diagrams Diagrams

that show the relative magnitude and that show the relative magnitude and direction of all forces acting upon an object direction of all forces acting upon an object in a given situation.in a given situation.

Contact Forces Contact Forces Applied ForceApplied Force Surface ForceSurface Force Friction Force Friction Force Air Resistance Air Resistance

ForceForce Tension ForceTension Force Compression ForceCompression Force Spring ForceSpring Force Lift ForceLift Force Thrust ForceThrust Force

Action-at-a-Distance Action-at-a-Distance ForcesForces

Force of GravityForce of Gravity Electrical ForceElectrical Force Magnetic ForceMagnetic Force

Types of ForcesTypes of ForcesName of ForceName of Force SymbolSymbol Description of the force.Description of the force.

Force of GravityForce of Gravity FFg g ←←

FFgravgrav

The force with which the The force with which the earth or other massively earth or other massively large object attracts large object attracts another object towards another object towards itself.itself. Is always directed Is always directed downwards downwards

Applied ForceApplied Force FFappapp A force which is applied A force which is applied to an object by a person to an object by a person or another object.or another object.

Types of ForcesTypes of ForcesName of ForceName of Force SymbolSymbol Description of the force.Description of the force.

Surface Force &Surface Force &Normal ForceNormal Force(Normal means (Normal means perpendicular)perpendicular)

FFsurfsurf ←←

FFNorm Norm

FFNN

The support force The support force exerted upon an object exerted upon an object which is in contact with which is in contact with a surface of another a surface of another object.object.

Friction ForceFriction Force FFff ←←

FFfricfric

The force exerted by a The force exerted by a surface as an object surface as an object moves across it or makes moves across it or makes an effort to move across an effort to move across it.it. Directed opposite of Directed opposite of motion.motion.

Types of ForcesTypes of ForcesName of ForceName of Force SymbolSymbol Description of the force.Description of the force.

Air Resistance Air Resistance ForceForce

FFairair A frictional force which A frictional force which acts upon objects as they acts upon objects as they travel through the air.travel through the air. Directed opposite of Directed opposite of motionmotion..

Tension ForceTension Force FFtenten The force which is The force which is transmitted through a transmitted through a string, rope, cable, or string, rope, cable, or wire (bridge deck) when wire (bridge deck) when it is pulled.it is pulled.

Types of ForcesTypes of ForcesName of ForceName of Force SymbolSymbol Description of the force.Description of the force.

Compression Compression ForceForce

FFcompcomp A force that acts to A force that acts to compress or shorten the compress or shorten the object it is acting on. object it is acting on.

Lift ForceLift Force FFliftlift A force that directly A force that directly opposes the weight of an opposes the weight of an “aircraft”“aircraft”..

Thrust ForceThrust Force FFthrustthrust The force that moves an The force that moves an “aircraft” though the “aircraft” though the airair..

Free Body DiagramsFree Body Diagrams The direction of the arrow shows the direction The direction of the arrow shows the direction

that the force is acting. that the force is acting. The size of the arrow in a free-body diagram The size of the arrow in a free-body diagram

reflects the magnitude of the force. reflects the magnitude of the force. Each force is labeled to indicate the exact type of Each force is labeled to indicate the exact type of

force. force. Represent the object by a box (or drawing) and Represent the object by a box (or drawing) and

draw the force arrows from the center of the box draw the force arrows from the center of the box outward in the direction that the force is acting. outward in the direction that the force is acting.

Can be any number of forcesCan be any number of forces

Forces on a WingForces on a Wing

Free Body Diagram of a WingFree Body Diagram of a Wing

Examples of F.B.D.Examples of F.B.D. Ex 1) Mr. Z. standing on the ground.Ex 1) Mr. Z. standing on the ground. Ex 2) As Mr. Z. is throwing a tennis ball Ex 2) As Mr. Z. is throwing a tennis ball

across the room to the left.across the room to the left. Ex 3) The tennis ball as it moves through Ex 3) The tennis ball as it moves through

the air after Mr. Z. has thrown it.the air after Mr. Z. has thrown it.

Free Body Diagram Free Body Diagram ActivitiesActivities

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Free Body DiagramsFree Body Diagrams ““Free Body Diagram Activities” Free Body Diagram Activities”

– – Due tomorrow Thurs. 11/7/13Due tomorrow Thurs. 11/7/13 ““Free Body Diagram Practice” Free Body Diagram Practice”

– – Due Friday 11/8/13Due Friday 11/8/13

Free Body Diagram Activities1) Sliding a book across the table to the right.

A) Before you slide the book.B) Sliding the book as it acceleratesC) Sliding the book with constant velocity.

2) Lightly kicking a tennis ball across the floor to the right.A) As you are kicking the ball.B) As the ball is rolling across the floor after the kick.C) When the ball comes to a complete stop.

3) Throwing a tennis ball straight up into the air.A) As you are throwing the ball in your hand.B) When the ball is going up.C) When the ball is coming down.D) When you catch the ball.

4) Throwing a paper airplane to the right.A) When you are throwing the paper airplane.B) When the paper airplane is in the air.C) As the paper airplane hits the ground.

5) The foot of a person walking to the right then stopping.A) Before the person starts walking.B) As the person is walking.C) As the person stops.

Free Body DiagramsFree Body Diagrams