EXAM I is coming up in two weeks! Multi-choice (scantron!) type of exam Some examples of possible questions will be available via the Exam link on our class web site (soon).

Just a little physics ….

MOTION Kinematics:The description of how things move in space. Position Velocity acceleration Dynamics:The prediction of why things move the way they do. Force Newton’s laws of motion Force of gravity

Kinematics: Position vs. time Bug’s trajectory

Kinematics: Position vs. time Bug’s trajectory. Bug was HERE at 10:01 PM

Kinematics: speed and velocity Bug’s trajectory. How fast was it going then? Bug was HERE at 10:01 PM

Bug’s trajectory. Bug was HERE at 10:01 PM.. 1 msec later Kinematics: speed and velocity

Bug’s trajectory. Bug was HERE at 10:01 PM.. 1 msec later 2/10 mm Kinematics: speed and velocity

Bug’s trajectory. Bug was HERE at 10:01 PM.. 1 msec later 2/10 mm SPEED: Kinematics: speed and velocity

Bug’s trajectory. Bug was HERE at 10:01 PM.. SPEED: 0.2 m/sec DIRECTION Kinematics: speed and velocity

Bug’s trajectory. Bug was HERE at 10:01 PM 0.2 m/sec VELOCITY = SPEED & DIRECTION Kinematics: speed and velocity At 10:01 PM the bug was doing 0.2 m/sec in the SW direction

Kinematics: velocity vs. time/position Velocity vectors: (Length ~ speed)

Kinematics: Acceleration.. 10:01 PM 1 msec later

Kinematics: Acceleration.. Acceleration = Change in velocity (Speed and direction) 0.2 m/sec 0.5 m/sec How is this done?

Kinematics: Acceleration Change in velocity (Speed and direction) 0.2 m/sec 0.5 m/sec How is this done? ?

Kinematics: Acceleration Change in velocity (Speed and direction) 0.2 m/sec 0.5 m/sec How is this done? VV Find length with ruler or trigonometry. Say it’s 0.15 m/sec direction

Acceleration = Change in velocity (Speed and direction) Acceleration = 0.15 m/sec = =

EXAMPLE 1: LINEAR MOTION

Acceleration =

EXAMPLE 1: LINEAR MOTION Acceleration =

EXAMPLE 1: LINEAR MOTION Acceleration =

EXAMPLE 1: LINEAR MOTION (De)acceleration =

EXAMPLE 1: LINEAR MOTION (De)acceleration =

EXAMPLE 1: CONSTANT ACCELERATION Gravity!

EXAMPLE 1: CONSTANT ACCELERATION Gravity! OR g

Speed (V) is constant but velocity is NOT EXAMPLE 3: UNIFORM CIRCULAR MOTION

Speed (V) is constant but velocity is NOT V Centripetal (center-seeking) acceleration EXAMPLE 3: UNIFORM CIRCULAR MOTION

Speed (V) is constant but velocity is NOT V Centripetal (center-seeking) acceleration

NEWTON! His “laws of motion” His law of gravitation + All of Kepler’s results, and then some!! AD

His “laws of motion” 1. An object that isn’t experiencing any net force moves with a constant velocity (At rest? → constant velocity of zero!) What’s force, and what does it do? 2. F = M×A ! What a (total or net) force does. What mass is. 3. Action & reaction. How objects interact! (the physics)

NL#1 An object that isn’t experiencing any net force moves with a constant velocity No force → velocity constant. So … Force ~ changing velocity (acceleration) (At rest? → constant velocity of zero!)

NL#2 Q: Why not just F = A ? A: Experience…. F = M A (mass times acceleration) The standard ‘force’ machine No pull No force Pulls with Standard force Pull here

Applying our standard force to…. 1 bowling ball produces twice the acceleration as … 2 bowling balls The same force applied to different objects does NOT produce the same acceleration!!

INERTIA: The tendency of an object to resist acceleration MASS: A measure of a specific object’s inertia! (HOW?) What it’s made of It’s size

INERTIA: The tendency of an object to resist acceleration NL#2 MASS: A measure of a specific object’s inertia! (HOW?) Applied standard force Measured acceleration Derived mass – new units e.g. kg or Slugs

NL#3 If object A exerts a force on an object B, object B must exert an equal but opposite force on object A. spaceman, mass = 1 spaceship, mass = 10,000

spaceman pushes on ship with force F spaceship accelerates to right at a rate A=F/10,000 At the same time ….

ship pushes back on spaceman with force F A=F/1

Spaceman flies off at an acceleration 10,000× that of the ship. Equal (opposite) forces, but very different accelerations A=F/1 A=F/10,000

Newton's laws tell us how a force affects the motion of an object. If we know the details of a force acting on an object, then we can use Newton’s Laws to calculate how an object will move! The POINT:

GRAVITY AND WEIGHT Observational fact: Everything drops with the same acceleration ( g ) in a gravitational field (at a given point). Feather and bowling ball:

WEIGHT Force of gravity on a body; e.g. “lbs.” Varies from place to place! Earth Mars Jupiter 180 lbs. 68 lbs. 426 lbs. For instance, on the surface of … Your weight would be … Near earth, at an elevation of … Your weight would be … 10 mi 100 mi 1000 mi 179 lbs. 171 lbs. 114 lbs.

MASS Intrinsic property of an object, it’s inertia to ANY force. Same everywhere. Earth 180 lbs. For instance, IF on the surface of … Your weight is … THEN … your mass is (82 kg) EVERYWHERE

FLOOR V = constant so … A = 0 so F total = 0 OUR SENSE OF WEIGHT

FLOOR FORCE DUE TO GRAVITY = Mg : 20 lbs. 180 lbs.

FLOOR 20 lbs. 180 lbs. FORCE DUE TO FLOOR: 20 lbs. 180 lbs. FORCE DUE TO GRAVITY = Mg :

180 lbs. Our physical sense of weight comes from a compressive feeling in our soft bodies NOW ….

“WEIGHTLESSNESS” FLOOR REMOVE FLOOR ….

“WEIGHTLESSNESS” 20 lbs. 180 lbs. FORCE DUE TO GRAVITY = Mg : BOTH STILL HAVE WEIGHT!! FREE FALL !!

“WEIGHTLESSNESS” But since F = Mg, Both accelerate downward with acceleration g They maintain their relative positions as they drop together FREE FALL !!

WEIGHTLESSNESS ‘Weightless’ cats!!

Astronaut Marsha Ivins Astronaut ?