1 Physics 1100 – Spring 2009 Review for Exam I Friday, February 27 th Chapters 1 - 10

1Physics 1100 – Spring 2009

Review for Exam IReview for Exam IFriday, February 27Friday, February 27thth

Chapters 1 - 10Chapters 1 - 10



Newton’s 1st lawNewton’s 1st law

If the total “resultant” force acting on an object is zero, then the object will either remain at

rest or it would move along a line with a constant velocity.


Newtons’ Second LawNewtons’ Second Law

• F = m a

• The acceleration of an object is directly proportional to the net force acting on the object…

• …and inversely proportional to the mass of the object.


Newton’s Third LawNewton’s Third Law

• Action-Reaction

• Whenever one body exerts a force on a second body…

• …the second body exerts an equal and opposite force on the first body.


Newton’s Laws in ReviewNewton’s Laws in Review

• 1st

– Law of Inertia

• 2nd

– F = m a

• 3rd

– Action/Reaction


Linear MotionLinear Motion

• Speed d = v t v = d / t• Velocity (magnitude & direction)• Acceleration a = f / m• Free Fall Velocity v = g t• Free Fall Distance d = ½ g t2


Chapter 4 - Newton’s Second LawChapter 4 - Newton’s Second Law

• F = m a• Friction• Mass• Weight• Terminal Velocity


Vector or Scalar?Vector or Scalar?

• Speed………..• Velocity……...• Acceleration..• Time………….• Distance……..• Force…………

scalar

vector

vector

scalar

scalar

vector


Mass Mass

• the quantity of matter in an object

• the measurement of the inertia

• measured in kilograms (kg)


WeightWeight• the force upon an object due to gravity

• Weight = Mass Acceleration of gravity

W = mg

• measured in Newtons (N) in the metric system or pounds (lb) in the British system


When Acceleration Is Zero...When Acceleration Is Zero...

• …we say the object is in Mechanical Equilibrium.

• …the net force is zero.


• Friction - a force that resists motion

– Static frictional force: when nothing is sliding

– Sliding frictional force: when surfaces are sliding

– Static frictional forces always greater than sliding ones

• Inertia - the resistance of an object to change in its state of motion

Friction


Free FallFree Fall


• Momentum - Inertia in motion– momentum = m v

– Impulse = F t = ∆ m v

• Inertia - the resistance of an object to change in its state of motion

Momentum


Energy definitions Energy definitions

• Potential Energy (due to Earth’s gravity) P.E. = m g h

• Kinetic Energy K.E. = ½ m v2

• Work (units: 1 N * 1 m = 1 joule = .239 calories) W = F d = ∆ Kinetic Energy

• Power (units: 1 joule / second = 1 watt) 1 Kilowatt = 1000 watts and 1 Megawatt = 1M watts 1 HorsePower = 746 Watts

P = W / t


Momentum and ImpulseMomentum and Impulse


Momentum & ImpulseMomentum & Impulse


Vector AdditionVector Addition


TorqueTorque

• Torque is the product of the force and lever-arm distance, which tends to produce rotation.

• Torque = force lever arm– Examples:

• wrenches

• see-saws


Rotational InertiaRotational Inertia • An object rotating about an axis tends to remain rotating

unless interfered with by some external influence.

• This influence is called torque.

• Rotation adds stability to linear motion.– Examples:

• spinning football

• bicycle tires

• Frisbee


• The greater the distance between the bulk of an object's mass and its axis of rotation, the greater the rotational inertia.

• Examples: – Tightrope walker

– Ring and Disk on an Incline

– Metronome


Centripetal ForceCentripetal Force

• …is applied by some object.• Centripetal means "center seeking".

Centrifugal ForceCentrifugal Force

• …results from a natural tendency.• Centrifugal means "center fleeing".


Circular MotionCircular Motion

• Linear speed - the distance moved per unit time. Also called simply speed.

• Rotational speed - the number of rotations or revolutions per unit time.

• Rotational speed is often measured in revolutions per minute (RPM).


Angular MomentumAngular Momentum

• Another conserved quantity is angular momentum, relating to rotational inertia:

• Spinning wheel wants to keep on spinning, stationary wheel wants to keep still (unless acted upon by an external rotational force, or torque)

• Newton’s laws for linear (straight-line) motion have direct analogs in rotational motion


GravityGravity

• Newton’s Universal Law of Gravitation:

F = GM1M2/r2


GravityGravity

• Weight • the force due to gravity on an object

• Weight = Mass Acceleration of Gravity

• W = m g

• Weightlessness - a conditions wherein gravitational pull appears to be lacking– Examples:

• Astronauts

• Falling in an Elevator

• Skydiving

• Underwater


Projectile MotionProjectile Motion

• Break the motion into 2 aspects, “components”– Horizontal

– Vertical

• There is no force acting in the horizontal direction– Horizontal velocity does not change

– Horizontal distance = time in air x horizontal velocity

• There is a force acting in the vertical direction – force of gravity!– Vertical velocity changes the same as if the projectile had been

thrown straight up (or dropped)

– Time in air determined by vertical travel


ProjectilesProjectiles



Projectile ExampleProjectile Example

• The boy on the tower throws a ball 20 meters downrange as shown. What is his pitching speed?

Use the equation for speed as a "guide to thinking.“ v = d/t

d is 20m; but we don't know t… the time the ball takes to go 20m. But while the ball moves horizontally 20m, it falls a vertical distance of 4.9m, which takes 1 second… so t = 1s.


Equation Sheet

Newton’s Law’s

• If FNet =0, then a =0

• If FNet >0, then FNet = ma

• FAB = - FBA

Linear Displacement• Speed v = d / t• Distance (constant speed) d = v t• Acceleration a = f / m• Velocity (constant a) v = a t• Distance (constant a) d = ½ a t2

• Free-fall acceleration = g = 10 m/s2

Weight• W = mg

Momentum• Momentum (p) = mv• Change in p (p) = Impulse = F t• System with no external force

pinitial = pfinal

Energy and Energy Conservation• E = PE + KE• PE = mgh• KE = ½ mv2

• Work = Fparallel x = E• Power (P) = Energy/time = E/t

Rotational Kinematics• Angular velocity = linear velocity/radius =v/r• v(linear) = r• Torque () = Force x Lever Arm• Rotational Inertia ()• Angular momentum L = • System with no external torque

Linitial = Lfinal

Gravity

• F = GMF = GM11MM22/r/r22

Units• Mass = kg (kilograms)• Distance = m (meters)• Force = kg m/s2 = 1 Newton• 1 Joule (J) = 1 N m• 1 Watt = 1J/s

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1 Physics 1100 – Spring 2009 Review for Exam I Friday, February 27 th Chapters 1 - 10