Transcript Slide 1
CA Preparation “Stretching”
Mr D Powell
Planning an Experiment
• • • • • • • Lets practice writing a plan… Identifying sources? (Basic) Identifying variables? (Basic) Explain how to control variables Write a risk assessment Write plan (Harder) (Basic) (Basic) Can you identify anomalous data on a graph? (Medium) 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.
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.
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) pH
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.
When you load a wire and stretch in it behaves in a proportional way.
If you double the force you also double the extension.
This only happens till you get to the “elastic limit” If you go beyond this the wire will permanently deformed 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 3 2,5 2 1,5 1 0,5 0 0,000 0,050 0,100 0,150
Extension (m)
0,200 Extension (m) 0.000
0.035
0.090
0.175
0.254
Force (N) 0 1 2 3 4 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?
iii 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. (Basic) 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)
Diameter of lobe hole
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Heaton
Michelle thinks that the lycra fabric of her shirt will extend when it is pulled at both ends.
(Basic)
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)
Extension
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