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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 at10:01 PM
Kinematics: speed and velocity
Bug’s trajectory
.
How fast was it going then?Bug was HERE at10:01 PM
Bug’s trajectory
.
Bug was HERE at10:01 PM
.
.
10:01 PM
1 msec later
sec001.0t
Kinematics: speed and velocity
Bug’s trajectory
.
Bug was HERE at10:01 PM
.
.
10:01 PM
1 msec later
sec001.0t
2/10 mmm0002.0d
Kinematics: speed and velocity
Bug’s trajectory
.
Bug was HERE at10:01 PM
.
.
10:01 PM
1 msec later
sec001.0t
2/10 mmm0002.0d
SPEED:
m/sec2.0
t
d
Kinematics: speed and velocity
Bug’s trajectory
.
Bug was HERE at10:01 PM
.
.
10:01 PM
SPEED:
m/sec2.0
t
d
0.2 m/sec
DIRECTION
Kinematics: speed and velocity
Bug’s trajectory
.
Bug was HERE at10:01 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
sec001.0t
Kinematics: Acceleration
.
sec001.0t
.
Acceleration =
Change in velocity(Speed and direction)
t
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?
DV
Find length with ruler or trigonometry.
Say it’s 0.15 m/sec
direction
Acceleration =
Change in velocity(Speed and direction)
t
Acceleration =0.15 m/sec
sec001.0t
=
2m/sec150m/sec/sec150
=
t
V
EXAMPLE 1: LINEAR MOTION
mi/hr50
0t
mi/hr50mi/hr50
0t sec 2t
EXAMPLE 1: LINEAR MOTION
Acceleration =
mi/hr/sec0
mi/hr50
0t
mi/hr70
sec 4t
EXAMPLE 1: LINEAR MOTION
mi/hr50
sec 2t
Acceleration =
mi/hr/sec10
mi/hr70
sec 4t
mi/hr50mi/hr50
0t sec 2t
mi/hr110
sec 6t
EXAMPLE 1: LINEAR MOTION
Acceleration =
mi/hr/sec20
mi/hr50
0t
mi/hr110
sec 6t
mi/hr40
sec 8t
mi/hr70
sec 4t
EXAMPLE 1: LINEAR MOTION
mi/hr50
sec 2t
(De)acceleration =
mi/hr/sec30
mi/hr0
sec 10t
mi/hr50
0t
mi/hr110
sec 6t
mi/hr40
sec 8t
mi/hr70
sec 4t
EXAMPLE 1: LINEAR MOTION
mi/hr50
sec 2t
(De)acceleration =
mi/hr/sec20
EXAMPLE 1: CONSTANT ACCELERATION
Gravity!
EXAMPLE 1: CONSTANT ACCELERATION
Gravity!
2m/sec8.9
ft/sec/sec32OR
g
Speed (V) is constantbut velocity is NOT
EXAMPLE 3: UNIFORM CIRCULAR MOTION
Speed (V) is constantbut velocity is NOTV
Centripetal (center-seeking) acceleration R
VA
2
R
EXAMPLE 3: UNIFORM CIRCULAR MOTION
EXAMPLE 3: UNIFORM CIRCULAR MOTION
Speed (V) is constantbut velocity is NOT
V
Centripetal (center-seeking) acceleration R
VA
2
R
NEWTON!
His “laws of motion”
His law of gravitation+All of Kepler’s
results, and then some!!
1642-1747 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 pullNo 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?)
volumedensity M
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?)
A
FM
Applied standard force
Measured acceleration
Derived mass – new units e.g. kg or Slugs
NL#3If 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 rateA=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
https://www.youtube.com/watch?v=7Mrkpcn-_YU
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 Jupiter180 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 mi179 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 slugs 6.5ft/sec32
lbs1802
g
FM (82 kg)
EVERYWHERE
FLOOR
V = constant so …
A = 0 so Ftotal = 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.
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
2m/sec8.9
They maintain their relative positions as they drop together
FREE FALL !!
WEIGHTLESSNESS
https://www.youtube.com/watch?v=O9XtK6R1QAk
‘Weightless’ cats!!
Astronaut Marsha IvinsAstronaut ?
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