StaticsStatics

Force is a push or pull caused by Force is a push or pull caused by the interaction between two the interaction between two objects. Forces that do not cause objects. Forces that do not cause motion are defined by the laws of motion are defined by the laws of Statics.Statics.

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Do all forces cause motion? Think Do all forces cause motion? Think of an example of a force that of an example of a force that does not cause an object to go does not cause an object to go into motion.into motion.

EquilibriumEquilibrium

When two or more forces are in When two or more forces are in perfect balance, they will cancel perfect balance, they will cancel each other out. This is called a each other out. This is called a state of state of equilibriumequilibrium..

Practice ProblemPractice Problem

Draw the free-body diagram for a Draw the free-body diagram for a book on a desk.book on a desk.

Book

Practice ProblemPractice Problem

Draw a free-body diagram of the Draw a free-body diagram of the desk as I push on it.desk as I push on it.

Practice ProblemPractice Problem

Draw the free body diagram of Draw the free body diagram of the object sitting on top of the the object sitting on top of the bookbook

Final Thought…Final Thought…

Draw a free body diagram of the Draw a free body diagram of the book.book.

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What would these spring scales What would these spring scales read?read?

10N

Force VectorsForce Vectors

A A vector quantityvector quantity is a is a measurement that represents measurement that represents both magnitude and direction.both magnitude and direction.

A A scalar quantityscalar quantity can be can be described by magnitude only.described by magnitude only.

Force is a vector quantity. Forces Force is a vector quantity. Forces are measured in Newtons (N).are measured in Newtons (N).

Combining VectorsCombining Vectors

When more than one force acts When more than one force acts on a body, they can be combined on a body, they can be combined to form a to form a resultant vectorresultant vector..

Combining parallel forces is as Combining parallel forces is as easy as adding (or subtracting) easy as adding (or subtracting) the magnitudes of each vector.the magnitudes of each vector.

Practice ProblemPractice Problem

Two teams are engaged in a tug Two teams are engaged in a tug of war. Team A pulls to the right of war. Team A pulls to the right with a force of 2500 N. Team B with a force of 2500 N. Team B pulls to the left with a force of pulls to the left with a force of 2000 N. What is the resultant 2000 N. What is the resultant force on the rope?force on the rope?

Parallelogram RuleParallelogram Rule

To find the resultant of two non-To find the resultant of two non-parallel vectors, construct a parallel vectors, construct a parallelogram where the two vectors parallelogram where the two vectors are sides.are sides.

The diagonal will be the The diagonal will be the resultantresultant.. An arrow of the same length in the An arrow of the same length in the

opposite direction as the resultant is opposite direction as the resultant is called the called the equilibrantequilibrant..

Practice ProblemPractice Problem

Find the resultant of the two Find the resultant of the two concurrent forces.concurrent forces.

19 N

13 N

Practice ProblemPractice Problem

Find the resultant of the two Find the resultant of the two concurrent forces.concurrent forces.

10 N

20 N

Composition of ForcesComposition of Forces

When two vectors are applied at When two vectors are applied at 9090oo, you can use right triangle , you can use right triangle geometry to calculate the geometry to calculate the resultant force.resultant force.

13 N

17 N

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Two forces are applied to an Two forces are applied to an object concurrently (at the same object concurrently (at the same time). time). – What angle will produce the greatest What angle will produce the greatest

resultant force?resultant force?– What angle will produce the least What angle will produce the least

resultant force?resultant force?

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A 15 N force due north and a 12 N A 15 N force due north and a 12 N force due east act concurrently force due east act concurrently on an object. What is the on an object. What is the resultant force acting on this resultant force acting on this object?object?

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A bushel basket holds about 125 A bushel basket holds about 125 medium apples. How much will medium apples. How much will this basket weigh? Will it be this basket weigh? Will it be difficult to lift?difficult to lift?

Resolution of ForcesResolution of Forces

One force acting on an object can One force acting on an object can be broken into perpendicular be broken into perpendicular components using trigonometry.components using trigonometry.

F = 1

0N

Fx = F cos

Fy = F sin

Practice ProblemPractice Problem

A 20 N force is applied to a block A 20 N force is applied to a block at an angle of 35at an angle of 35oo above above horizontal. What are the vertical horizontal. What are the vertical and horizontal components of this and horizontal components of this force?force?

Practice Problem Practice Problem

A 20N block is placed on top of an A 20N block is placed on top of an incline that is 20incline that is 20oo above above horizontal. How much force is horizontal. How much force is gravity exerting on the block that gravity exerting on the block that is directed down the incline?is directed down the incline?

20o

Final Thought…Final Thought…

A wagon is pulled along a level A wagon is pulled along a level sidewalk with a force of 100N. If sidewalk with a force of 100N. If the wagon handle is at an angle the wagon handle is at an angle of 37of 37oo, how much of that force is , how much of that force is pulling the wagon horizontally?pulling the wagon horizontally?