Chapter 2

Section 2.1

2.1 con’t  Physical interactions change the behavior (motion, temp. etc…) of matter.  Ex. Of interaction forces…  kick a soccer ball…  force of foot on ball…force of ball on foot

Long Range forces…  Do not have to be touching  ex. Gravity  Terms..  magnitude- “how much”  weight- result of both mass and gravity  Other examples of long range forces…  electric, magnetic

2.1 con’t  Contact forces…  as you would think… must be touching hence “contact”  ex. Foot on a soccer ball  Recognizing forces…link  tlaws/u2l2b.cfm tlaws/u2l2b.cfm

Measuring forces  In U.S. - calibrated to measure in lbs.  SI unit is the Newton  Conversion factor  1 lb = N or 1 N =.2248 lbs  In general… a force is measured by the deformation which is the change in the size or shape it produces.

Force is a vector quantity  Vectors- have both magnitude and direction  Other examples of vectors…  a) position  b) displacement  c) displacement  d) acceleration  e) momentum  f) angular momentum  g) torque  h) electric and magnetic field

Section 2.1 cont  Scalars and vectors…  Scalar- only magnitude…NO direction  ex. Mass  300 kg  kg  500 kg

 Link to scalars and vectors  ors/U3L1a.cfm ors/U3L1a.cfm in/U1L1b.cfm

Mops…  Minds on Physics problems  s.cfm s.cfm  Kinematic concepts assignments…  1 and 2

Section 2.1 cont  Ex. Problem 2.1 Practice prob. 2.1

Section 2.2  Graphical Vector Addition  Head to tail method  Link to vector addition  ors/U3l1b.cfm ors/U3l1b.cfm

Mops… for section 2.2  Minds on Physics problems..  s.cfm s.cfm  Vectors/projectiles  Assignment 1, 2, 3, 4, and 5

Section 2.2 cont  Ex. Problem 2.2 practice problem 2.2

Section 2.3  Vector addition using components… Link  ors/U3L1d.cfm ors/U3L1d.cfm The resultant vector is the sum of the  X and the Y components.  ors/U3L1eb.cfm ors/U3L1eb.cfm

Section 2.3  Mops for section Forces in two dimension  assignment # 1 Vector/projectiles  assignment # 7  Ex. Problem 2.3 and 2.4 practice prob 2.3 and 2.4

Section 2.4  Inertia and Equilibrium…  Newton’s first law of motion  For motion to occur…must have net force?  True or False?  To identify motion… must have a frame of reference.

2.4 cont  Net force…is vector sum of all the forces acting on an object.

First law states… ( also called law of inertia)  An object in motion will stay in motion unless a net force acts upon it….and  *** if in constant motion… net force is zero  An object at rest will stay at rest unless a net force acts upon it.  Link Mops…Newton’s laws Assignment  s.cfm s.cfm

Newton combined ideas of the past for his complete idea  Galileo- Inclined plane/ball…based on no friction.  Idea Contradicted Aristotle who thought everything is at rest so motion would require a net force  Descartes added “in a straight line”

Section 2.4 cont  Ex. 2.5 and practice 2.5  Know free body diagrams…  Link  tlaws/U2L2c.cfm tlaws/U2L2c.cfm

Section 2.4 cont  Translational equilibrium has a net force of zero  Spring scales measure weight…equal and opposite of gravity.  springscales.html springscales.html

Section 2.4 cont  Ex. 2.6 and 2.7  And  Practice prob. 2.6 ; 2.7 and 2.8

Section 2.5 Interaction pairs  Newton’s 3 rd law  Force- Always in pairs…called interaction pairs.  Ex. Push the door… the door pushes you  3 rd law states- interaction partners always have the same magnitude and in opposite direction.  Link  ws/U2l4b.cfm ws/U2l4b.cfm

2.5 cont  Ex. Problems 2.9 practice prob. 2.9  Checkpoint 2.5  ***Sometimes two equal and opposites acting on same object… not interactive.

2.5 cont.  Internal and External forces  Internal-Both interacting objects are part of the system, and forces add to zero  External- not so  Link… (Review all sections)  u5l2a.cfm u5l2a.cfm  Mops… Newton’s laws  Assignment… 12

Section 2.6 Gravity Forces  Newton’s law of universal gravitation   F= Gm 1 *m 2  r 2  W=mg Weight = mass* gravity  g = 9.81N/kg  Link (Review all sections)  u6l3c.cfm u6l3c.cfm

2.6 cont  Ex. Problem 2.11 practice prob  Checkpoint 2.6  Mops… Newton’s laws  Assignments 6; 7; and 8

Section 2.7 Contact forces Normal Force… Contact force which is perpendicular To the contact surface…prevents two objects from passing through one another. Checkpoint 2.7 Examples are in types of forces link

2.7 cont.  Friction… a constant force parallel to the contact surface.  a) static friction… “stationary”  b) kinetic friction…”moving”  Fsmax is proportional to N force  better traction in snow??? How  fs= us N  Fk= uk N

Section 2.7 cont  Ex and 2.13  Practice prob and 2.13 Friction is explained on previous link Microscopic origin of Friction…Skip!

Sect 2.7 cont.  Equilibrium on an inclined plane  Link  ors/U3L3e.cfm ors/U3L3e.cfm  Ex. Prob Practice prob. 2.14

2.8 Tension  Tension and pulley systems  Link  ors/U3L3f.cfm ors/U3L3f.cfm  Ex. Problems 2.15 and 2.16  Practice problems 2.15 and 2.16  Plus… Many others!!!

2.8 cont.  Mops…newton’s laws  Assignment… # 4

Section 2.9  Fundamental Forces  Forces have 4 different types of interactions…  a) Gravity… the weakest. Gets weaker as the distance increases, but never gets to zero  b) Electromagnetism…acts on particles with electric charge…binds electrons to nucleus. Ex. Solids, liquids, gasses, also friction and normal force. Springs; muscles; and wind. **much stronger than gravity

2.9 cont.  c) Strong … atoms  d) weak force Radioactive decay particles 

End of Chapter 2 concepts  Link is in chapter 2 HW/Lab folder