Transcript 2007_SeeS_PhysicsofMotion_Stations

SeeS
Distance
How much ground an object has
covered
Velocity
How fast an object is going in a
certain direction.
Acceleration
How quickly an object slows down or
speeds up.
Force
A push or pull that causes an object
to move, stop, or change direction.
The larger the weight, the larger the force.
The larger the force, the larger the acceleration.
Video
The Ultimate Race!
Jet Fighter vs Car vs Motorcycle
1.00
• Plane passes bike at about 20
seconds [A]
Position(mile)
Position versus Time
0.75
Car: Porsche
Jet: Jaguar
Motorcycle: Ninja
0.50
• Car passes bike at about 25
seconds [B]
• Plane needs about 2000 ft to
take off
0.25
0.00
0
5
10
Velocity (mph)
20
25
30
Time (sec)
350
300
15
Velocity versus Time
Car: Porsche
Jet: Jaguar
Motorcycle: Ninja
250
200
CAR:
top speed 200 MPH (325 km/hr or
90 m/sec).
150
100
50
0
0
5
10
MOTORCYCLE:
top speed 175 MPH (280 km/hr or
80 m/sec).
15
Time (sec)
20
25
30
JET FIGHTER:
top speed 1,400 MPH (about
MACH 2)
take off speed 200 MPH.
Jet Fighter versus Car versus Motorcycle
MOTORCYCLE: Accelerates fastest off the starting line
(because it is the lightest). But its top speed is only
about 175 MPH (280 km/hr or 80 m/sec).
CAR: Accelerates second fastest off the starting line
(because it is the next lightest).
But top speed is only about 200 MPH (325 km/hr or 90
m/sec).
JET FIGHTER: Slowest of the starting line (it is by far the
heaviest). But is accelerates for the longest time - 0.6
g for more than 25 seconds.
But top speed MACH 2 or 1,400 MPH with a take off
speed of about 200-250 MPH.
Sprinter 100 m Split Times
World Record & Grade 5s
100
90
Position (meter)
• Sprinters accelerate fairly quickly
(2 to 4 seconds) and then try and
keep at that speed (velocity).
Sprinter Position
80
70
60
World Record:
100 meters in about 9.7 s
Top speed about
12 meters/second or
27 MPH
50
World Record
40
Grade 5: Fastest
30
20
Grade 5: Average
10
0
0
2
4
6
8
10
Time
12
14
16
18
World Record
Sprinter Velocity
Grade 5: Fastest
Velocity
15
Grade 5: Average
10
5
0
0
2
4
6
8
10
Time
12
14
16
18
Grade 5 Fastest
100 m in about 13.8 s
Top speed about
8 meters/second or
18 MPH
Grade 5 Fastest
100 m in about 17 s
Top speed about
7 meters/second or
15 MPH but fades at end.
Sprinter 40 m Split Times
World Record & Grade 5s
Position (meter)
40
Sprinter Position
30
20
World Record
Grade 5: Fastest
10
Grade 5: Average
0
0
2
4
Time
6
8
World Record
Velocity
Grade 5: Fastest
Grade 5: Average
10
5
0
0
2
4
Time
6
8
World Record:
40 meters in about 4.5 s
Top speed about
12 meters/second or
27 MPH
10
15
Sprinter Velocity
• Sprinters accelerate fairly
quickly (2 to 4 seconds) and
then try and keep at that speed
(velocity).
10
Grade 5 Fastest
40 m in about 6.5 s
Top speed about
8 meters/second or
18 MPH
Grade 5 Fastest
40 m in about 7.2 s
Top speed about
7 meters/second or
15 MPH and no fade! 1
Fast Cars over a ONE MILE Drag Strip
Friction
A force that happens when things
rub against each other.
Gravity
The force of attraction between all
masses in the universe
Frequency
The number of times something
happens within a given time period.
Friction
Supplies:
•
•
•
•
•
•
Spring scales
Weights
String
Boxes
Surfaces
Clamps
Procedure:
•
•
•
•
•
•
•
•
•
Clamp down the various surfaces.
Connect spring scale to box with string.
Place various weights in boxes.
Start with box on table top (no surfaces).
What’s Happening:
Pull on scale to move box with a constant velocity.
Experiment with surfaces attached to boxes with
• The rougher surfaces have more friction and
binder clips and surfaces on table in many
require more force to overcome static and
combinations.
kinetic friction. Conversely, smoother surfaces
Use the readings on the scale to determine, with a
require less force. Again Newton’s 2nd law
given weight, how rough the surfaces are (i.e. how
applies, the force required to move the box a
much friction they have).
constant velocity is the same as the force of
Have kids identify the roughest and smoothest
kinetic friction.
surfaces and combinations.
Discuss differences in force required to begin moving Notes:
and keep moving, describe stationary and moving
• Teflon should be applied to the box like skis.
friction.
•
Note the differences in the grit of the
sandpaper.
Friction – Kinetic and
Static
Left: Contact between
surfaces
Force – An action that causes a body to accelerate
Friction – A force that resists motion between surfaces
Static Friction – The force that resists the motion of an
object while it’s at rest
Kinetic Friction – The force that resists the motion of an
object while it’s moving
Left: Static
Friction
Right:
Kinetic
Friction
Sliders
Definitions:
•
Velocity
• Acceleration
• Gravity
• Tension
Procedure:
•
•
•
•
•
•
•
•
•
Demonstrate spring scale
measuring force
(weight on the scale).
Put box on cart.
Attach spring scale to cart with string.
Put weights in box.
Pull on spring scale and see how much force it
takes to make the cart do various things
(constant velocity and acceleration).
Replace box on cart with mystery mass and
repeat the process.
Guess the value of the mystery mass.
Set up pulley and attach it to table, using
clamp.
Use weights on end of string to pull.
cart
pulley
mass
What’s Happening:
•
Newton's Second Law: the amount of force is
directly related to the mass and the
acceleration (the greater the mass, the lower
the acceleration for a given force)
Notes:
•
Try constant acceleration, force, and velocity.
Sliders
Definitions:
•
Velocity
• Acceleration
• Gravity
• Force
Procedure:
•
•
•
•
•
•
•
•
Put mystery boxes/weights
cart
on cart.
pulley
Have kids line up and push
mystery box carts. (Figure
which is heaviest without lifting.)
mass
Demonstrate spring scale measuring force
(weight on the scale).
Attach spring scale to cart with string.
Pull on spring scale and see how much force it What’s Happening:
takes to make the cart do various things
• Newton's Second Law: the amount of force is
(constant velocity and acceleration).
directly related to the mass and the
Set up pulley and attach it to a table. If not the acceleration (the greater the mass, the lower
table, then to a board and attach that to the
the acceleration for a given force)
table.
Notes:
Use weights on end of string to pull.
• Try constant acceleration, force, and velocity.
Pendulum
•An object on a wire or arm fixed to a spot.
•The object can then swing back and forth.
•They can be used for fun.
•Swings
•Amusement Park rides
•Desk toys
•They can also be used to measure time.
•They were used in early clocks.
• Grandfather Clocks
• Metronomes
•Most are powered by gravity.
Pendulum
Pendulum Free Body Diagram •Gravity pulls down.
•The tension pulls towards pivot point.
•The resultant force makes the
pendulum swing.
θ
•Pendula are simple harmonic
oscillators (at least at small angles θ).
•The natural frequency is: ω = g
l
T
T
l
•So the period is: T = 2π l
g
mg ΣF
mg
ΣF
•The time for a full swing
is only dependant on
gravity and the length.
• That’s how grandfather
clocks and metronomes
originally worked.
√
√
Pendula
Definitions:
•
•
Frequency
Period
Procedure:
•
•
•
Loop ropes through basketball goal.
Attach mass bob to one and mesh bag to other.
Make certain they are at right angles (one swings
in x and the other in y).
• Place chair in arc of mesh bag.
• Place Shotput in mesh bag.
• When kids arrive ask about pendula.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Point out everyday pendula.
Swing bob pendulum at medium height timing it.
Tell kids the time, and shorten the length.
Ask kids if it will take longer of shorter to swing.
Repeat the swing and time.
Tell the time (shorter), and length a lot.
Ask kids if it will take longer or shorter to swing. What’s Happening:
• The total force on the mass (gravity and the
Repeat the swing and time and tell (longer).
rope) causes it to swing back and forth.
Return to first middle height, remind of time.
• The pendulum is a simple harmonic oscillator at
Add additional bob.
small angles, with a known frequency (g/l)^.5,
Ask kids if it will take longer or shorter to swing. making it a reliable time gauge, independent of
mass.
Swing and time, (no change).
• The shotput part illustrates conservation of
Finally one at a time have kids sit in chair.
energy. The mass cannot go above its original
If possible have something behind their head
height.
keep it still.
Notes:
• Bring the Shotput up to their nose and let go.
• Only release the shotput, DO NOT PUSH.
• It will come back very close, but not hit.