Inspiraling Compact Objects: Detection Expectations Vicky Kalogera Physics & Astronomy Dept.
Welcome to Physics Main Principal #1: Physics is the study of moving objects! We want to be able to...
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Transcript of Welcome to Physics Main Principal #1: Physics is the study of moving objects! We want to be able to...
Welcome to PhysicsWelcome to Physics
Main Principal #1: Physics is the study of moving objects!
We want to be able to predict how objects will move in all situations
But here’s the problem:
Q: How do you know if an object
is actually “moving”? A: When it’s “changing position” (travelling
a certain distance)?If a person is “standing still”, we assume he/she is “not moving”
But what about the planet that person is standing on?
Is the person therefore “moving” anyway?
So how do we tell if something really is “moving”?
It is moving around a star!!!
Oh boy; welcome to physics!!!
We use a principal called: “Point of Reference”
The hands on a clock don’t seem to move; but they are constantly
moving very slowly!
Are the passengers in a boat moving compared to a person standing on the shore?
Or is the person standing on the shore moving compared to the boat in the water?
Fwew! It can be tricky!
“PoR” means: what appears to be moving to you?
It can be tricky to really know what is moving and what isn’t!
Main Principal #2 & 3:
• #2: Basically, (if you really think about it) #2: Basically, (if you really think about it) all all objectsobjects are are movingmoving some amount, some amount, all the all the timetime..
• #3: We #3: We comparecompare the motion of the object that the motion of the object that appears to moveappears to move to a “ to a “stationarystationary” object ” object (one that doesn’t appear to move).(one that doesn’t appear to move).
An object is moving “slowly” if it moves a short distance in a long time.
An object is moving “quickly” if it moves a long distance in a short time.
There are several ways we use to describe the motion of an object:
“Velocity” and “Speed”
• Think: What are two ways to increase speed (go faster)?– Increase distance traveled in the same amount of time – Decrease the time it took to go the original distance
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s
m
Time
cetanDisVelocity
***Since they are almost the exact same thing, “Speed” and “Velocity” are used for the same motion
“Speed” means distance travelled in a certain amount of time
“Velocity” is the speed in a certain direction
Speed =Formula for Speed:
Graphs can help us Interpret what has actually happened!
The shape of the line and steepness of the The shape of the line and steepness of the “slope” can tell us what has happened and “slope” can tell us what has happened and
how fast it occurred!how fast it occurred!
That’s right! We are NOT done with graphs!!!
We are only just beginning!!!
Graphing Velocity
What you want to be able to do is know what the graph is telling
you by looking at the line…
This is NOT the graph for your notes...
Time
Interpreting Velocity on a Graph
Think of the Velocity graph this way: Which one of these balls will fall faster?
5 m
15 m
10 m
15 s10 s5 s
More DistanceIn Less Time
(Faster)
The graph with more steepness is the faster velocity. The less steep, the slower.
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s
m
Time
cetanDisVelocity
Dis
tanc
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Less DistanceIn More Time
(Slower)
You can use the slopeof a line to find Velocity
Draw this graph in your notes…
Interpreting Speed on a Graph:
5 m
15 m
10 m
15 s10 s5 s
It can help to think about the speed of a
rolling ball on the slope
Dis
tanc
e
Time
Stopped moving!Started slowly…
Now it’s moving fast!
As a group, describe how fast the object is probably moving as you travel along the line (left to right)
(After you try it together, click to see the real motion)
Q: HOW CAN YOU TELL?!?!
This ball would roll slowly…
This ball won’t roll at all!
This ball would roll fast!
Q: What should you learn from this? Q: What should you learn from this? A: Steep lines on motion graphs, mean an object is moving quickly! Non-steep lines mean the object is moving slowly!
Draw this graph in your notes…
Time (min)
Dist.(meters)
1
2
3
4
5
100
220
300
430
500
But this graph is not the whole story!!! It all can change if you pick different variables to graph!
100 m/min
110 m/min
100 m/min
107 m/min
100 m/min
Speed
Graphing Speed:The two lines look different, but still describe the same objects motion!
What should we learn? WATCH YOUR VARIABLES CAREFULLY!
Time (min)
Dis
tanc
e (m
)S
peed
(m
/min
)
This is basically the line of the data you see in the table…Let’s dim that last line but keep it here to compare to the new line…
Now we graph the line of this data…
Houston; um…Where
are we going?
• Think: How would you describe the motion of floating balloons?
• Do they move in a “constant” speed or direction? (“constant” means: “staying the same”)
The movement of a balloon is a great example of an object
Accelerating!
Balloons just kinda move all over the place. Sometimes they go straight up, sometimes they fly more sideways. CRAZY!
What is “Acceleration”?
• A: The rate at which velocity changes!
– In other words: How fast something speeds up, slows down, or even changes direction.
Speeding up: Slowing down: Changing direction:
You probably think it simply means to “speed up.” Well yes, and a bit more:
Acceleration = A change in Velocity
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m
Time
VelocityonAccelerati
You already learned the Velocity equation:
Here is the equation for Acceleration:
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s
m
Time
cetanDisVelocity
Means “change”
So how do you do that?
Final Velocity – Start Velocity
Final Time – Start Time
____________________=
Like this:
Time
Interpreting Acceleration on a Graph
5 m/s
15 m/s
10 m/s
15 s10 s5 s
Dis
tanc
e
This is the line of an object with an “constant velocity”
Compare it to the line of an object with a changingVelocity = Acceleration!
It is also possible to have an object with a negative acceleration
We can call this “Deceleration”
Notice the downward curveIt is a nice straight line!
Straight lines on a graph mean “constant”
Curved lines mean a changehas occurred = Acceleration!
Vel
ocity
Notice also, the different Y-axis variable!Notice also, the different Y-axis variable!
Acceleration Graphing Practice
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m
Time
VelocityonAccelerati
Time Dist. Acc.
1
2
3
4
5
2 m
8 m
18 m
32 m
50 m
2 m/s2
2 m/s2
2 m/s2
2 m/s2
2 m/s2
Think: Why is the acceleration staying the same if the car is speeding up more and more?
Now try and graph both the Speed line AND the Acceleration line. Compare them! Do this on the very back page of your packet!