Download CA Preparation Stretching P2

CA Preparation
“Stretching”
Mr D Powell
Planning an Experiment
Lets practice writing a plan…
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Identifying sources? (Basic)
Identifying variables? (Basic)
Explain how to control variables (Basic)
Write a risk assessment (Basic)
Can you identify anomalous data on a graph? (Medium)
Write plan (Harder)
Theory: the extension of an elastic object is directly proportional to the
force applied, provided that the limit of proportionality is not exceeded:
F = ke
F, is the force in Newtons, N
k, is the spring constant in Newtons per metre, N/m
e, is the extension in metres, m
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A force applied to an elastic object such as a spring will result in the
object stretching and storing elastic potential energy.

A spring by it’s nature wants to be
coiled.
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If you apply a force using a weight it
works against the structure of the
spring
The more force applied the more it
will extend.
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If we release the spring the “work”
that we have “done” (WD = F x d) is
recovered as it is “stored” inside the
spring.
The sankey diagram shows what
occurs when a spring is released.
EPE
Spring
Kinetic
Thermal (wasted)
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For an object that is able to recover its original shape, elastic
potential energy is stored in the object when work is done on the
object to change its shape.
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When you load a wire and stretch in
it behaves in a proportional way.
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If you double the force you also
double the extension.
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This only happens till you get to the
“elastic limit”
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If you go beyond this the wire will
permanently deformed
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Below this the wire acts like a spring
and you recover the “Work Done”
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d) The extension of an elastic object is directly proportional to the
force applied, provided that the limit of proportionality is not
exceeded:
Spring Extension... Hookes Law
 We need to think about the form
F = k∆L
 Where the force is related by a
constant for the spring.
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Example Results for one spring
Force (N)
4.5
4
3.5
Extension (m)
Force (N)
0.000
0
0.035
1
0.090
2
0.175
3
0.254
4
Force (N)
3
2.5
2
1.5
1
0.5
0
0.000
0.050
0.100
0.150
Extension (m)
0.200
0.250
0.300
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Research...
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Variables....
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Write your Exp up in “Prose”
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What do these graphs show?
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TASK: On your whiteboard describe each trend
as clearly as you can
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Dealing with Case Studies
How can we extract information from a
case study…
1. Identifying variables? (Basic)
2. How are tables and graphs labelled?
(Basic)
3. Can you identify anomalous data from
a table? (Medium)
4. Can you explain a trend? (Basic)
5. Can you identify anomalous data on a
graph? (Medium)
6. Linking to a hypothesis? (Harder)
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Questions to think about for your card…..
1. What is the independent variable? Is it categoric or continuous?
How do you know this?
2. What is the dependent variable? Is it categoric or continuous?
How do you know this?
3. What units do the variables have?
4. Are there any control variables?
5. Has a mean been taken & why?
6. Any anomalous data you can see?
7. Are the repeat values concordant?
8. What type of graph is this (if appropriate)
9. Does the graph have a basic trend?
10.Does the graph have a more complex trend?
11.What is the trend actually showing i.e. as X does this Y does this…
because…..
12.Does it support the hypothesis?
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Adele
Adele thinks that more bacteria will be killed if the concentration of
antibiotic increases. (Basic)
Adele also thinks that the bacteria will be killed in a larger diameter
circle if the concentration of antibiotic increases. But this effect
will trail off as the relationship depends on area not diameter
(Harder)
Adele has a
“strep” throat
and needs to kill
those bacteria
fast!
killed
Bacteria growth
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Beyonce
Beyonce thinks that the spring in her exercise machine will
extend when a weight is added (Basic)
Beyonce also thinks that the extension of the spring will be
directly proportional to the force applied by adding the
mass. (Harder)
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Timberlake
Justin has decided to get a ear stretcher
installed. But he is not sure on how much
he wants his ear to extend. He thinks of a
couple of ideas of how it might work…
I think that the force applied due to the
increase in size of the ring will increase
the diameter of my earlobe. However, the
force required for the same increase in
diameter will need to be more as the
diameter gets larger until my earlobe rips.
(Harder)
Force applied
I think that the force applied due to the
increase in size of the ring will increase
the diameter of my earlobe. (Basic)
Diameter of lobe hole
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Heaton
Michelle also thinks that the lycra fabric will
extend when it is pulled at both ends
when a force is applied. The relationship is
not linear and will extend less and less for
the same increase in force until it tears.
(Harder)
Force applied
Michelle thinks that the lycra fabric of her shirt
will extend when it is pulled at both ends.
(Basic)
Extension
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