Physics 534 Chapter 8

8/8/2019 Physics 534 Chapter 8

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Chapter 8Chapter 8



G.U.T.G.U.T.



ForceForce A f orceA f orce is a push or pull upon an objectis a push or pull upon an object

resulting from the object'sresulting from the object's interactioninteraction withwithanother object.another object.

Whenever there is anWhenever there is an interactioninteraction between twobetween two

objects, there is a force upon each of theobjects, there is a force upon each of theobjects.objects.

Contact f orcesContact f orces are forces which result when theare forces which result when thetwo interacting objects are physically contactingtwo interacting objects are physically contactingeach other.each other.

ActionAction--atat--aa--distance f orcesdistance f orces are forces whichare forces whichresult even when the two interacting objects areresult even when the two interacting objects arenot in physical contact with each other, yet arenot in physical contact with each other, yet areable to exert a push or pull despite their physicalable to exert a push or pull despite their physicalseparation.separation.



Examples of ForcesExamples of Forces

Contact ForcesContact Forces ActionAction--atat--aa--DistanceDistance

Frictional ForceFrictional Force Gravitational ForceGravitational Force

Tension ForceTension Force Electrical ForceElectrical Force

Normal ForceNormal Force Magnetic ForceMagnetic Force

Air Resistance Force Air Resistance Force

Applied Force Applied Force

Spring ForceSpring Force



Exam QuestionExam Question

A bowling ball rolls down a bowling alley.

Among the following, what causes its motion?

A) The instantaneous speed

B) The length of the alley

C) The mass of the ball

D) The initial force applied to the ball



Force UnitForce Unit

Force is a vector quantity which isForce is a vector quantity which is

measured using the standard metric unitmeasured using the standard metric unit

known as theknown as theN

ewton or NN

ewton or N

.. One Newton is the amount of forceOne Newton is the amount of force

required to give a 1required to give a 1--kg mass ankg mass an

acceleration of 1 m/s/s.acceleration of 1 m/s/s.

1N = 1kg1N = 1kgm/sm/s22



ActivityActivity

Page 173: Activity Forces: Part APage 173: Activity Forces: Part A

Draw Force Diagrams for each of theDraw Force Diagrams for each of the

situationssituations..



Adding Force VectorsAdding Force Vectors

Vectors may be added tip to tail.Vectors may be added tip to tail.



Equilibrium ForceEquilibrium Force

When a system of forces is in equilibrium,When a system of forces is in equilibrium,

the net Force, F the net Force, F net , is said to be 0., is said to be 0.

So if we add 2 or more force vectorsSo if we add 2 or more force vectorstogether, if the net Force is 0, then thetogether, if the net Force is 0, then the

sum of the vectors should be 0.sum of the vectors should be 0.

If the net Force is unbalanced, another If the net Force is unbalanced, another

vector can be added to achieve a netvector can be added to achieve a net

Force of 0.Force of 0.



Exam QuestionExam QuestionA ire is suspended rom the ceiling o a room. A 10 N eight is attached to the end o

the ire. The mass is then subjected to a horizontal orce o 6.5 N. (The igure belo isnot dra n to scale.)

F

What angle is ormed bet een the ire and the vertical

A) 33°

) 41°

) 49°

) 57°



Exam QuestionExam QuestionT h r e e o r c e s o 1 0 N a r e a p p l i e d t o a t r o l l e y o n a h o r i z o n t a l s u r a c e .

= 1 0 N2

= 1 0 N3

= 1 0 N1

4 5 º

4 5 º

p

p

p

F

F

F

W h i c h o t h e o l l o i n g g r a p h s i l l u s t r a t e th e e q u i l i b r iu m o t h i s s y s t e m

1 0¡ 2

1 0¡ 3

1 0¡ 1

4 5 ¢

4 5 ¢

2 4 , 1¡

F

F

F

E

p

p

p

p

A )£ 1 0

¤

2

£ 1 0¤

3

£ 1 0¤

1

4 5 ¥

4 5 ¥

£ 2 4 , 1¤

F

F

F

E

C )

p

p

p

p

= 1 0 N 2

= 1 0 N 3

= 1 0 N 1

4 5 º4 5 º

= 1 0 N

F

F

F

E

)

p

p

p

p

= 1 0 N2

= 1 0 N3

= 1 0 N1

4 5 º4 5 º

¦

)F

F

F E

p p

p

p



ActivityActivity

Do the Lab on page 177: Addition of Do the Lab on page 177: Addition of

Forces in Static EquilibriumForces in Static Equilibrium

Page 180, Practice a,b,c,dPage 180, Practice a,b,c,d Use drawings and/or trig.Use drawings and/or trig.



Hooke¶s LawHooke¶s Law

Hooke¶s Law states that the amount of deformation (squish or stretch) of anelastic object (e.g. a spring) is proportional

to the forces applied to deform it. F = kx

F is the Force in Newtons

x is the length of stretch in metres k is the constant of proportionality, specific

to a spring ± Unit is N/m



Hooke·s Law Hooke·s Law



Exam QuestionExam QuestionJimm y applies force to a spring-platform in order to com press it. For each force, he notes

the corresponding distance the spring is compressed.

X

F

He draw s a graph of the force F as a function of the compressed distance x.

W hat type of line should they obtain on the graph?

A) B) C) D)

x

F

x

F

x

F

x

F



ActivityActivity

Page 183, Q. 1Page 183, Q. 1--33

Lab: Hooke¶s Law.Lab: Hooke¶s Law.

Page 181.Page 181.



SummarySummary F

orce is a push or pull on an object, measuredF

orce is a push or pull on an object, measuredin Newtons (N).in Newtons (N).

Mass is the amount of matter in an object,Mass is the amount of matter in an object,measured in kilograms (kg).measured in kilograms (kg).

When adding forces along the same straightWhen adding forces along the same straightline, consider the forces in one direction asline, consider the forces in one direction asbeing positive, and the other direction, negative.being positive, and the other direction, negative.

The sum of the forces is called the unbalancedThe sum of the forces is called the unbalancedor net force, For net force, Fnetnet..

A vector diagram is used the determine the net A vector diagram is used the determine the netforce.force.

Hooke¶s Law states that the deformation of anHooke¶s Law states that the deformation of anelastic object, such as a spring, is directlyelastic object, such as a spring, is directlyproportional to the forces applied to it.proportional to the forces applied to it.



ActivityActivity

0, Q. 2,3,5,9, 11Page 190, Q. 2,3,5,9, 11--1313

Physics 534 Chapter 8

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