CA Preparation “Stretching” Mr D Powell. Mr Powell 2012 Index Mass Distance Temperature Length Newton's Time Velocity pH Concentration Planning an Experiment.

CA Preparation “Stretching”

KS4 ADDITIONALMr D Powell

Mr Powell 2012Index

Mass Distance

TemperatureLengthNewton'sTime Velocity pHConcentration

Planning an Experiment

Lets practice writing a plan…

• 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, Nk, is the spring constant in Newtons per metre, N/me, is the extension in metres, m

Mr Powell 2012Index

Mass Distance


A force applied to an elastic object such as a spring will result in the object stretching and storing elastic potential energy. A 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.

Kinetic

Thermal (wasted)

EPE Spring

Mr Powell 2012Index

Mass Distance


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.

A 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”

Mr Powell 2012Index

Mass Distance


d) The extension of an elastic object is directly proportional to the force applied, provided that the limit of proportionality is not exceeded:

ASpring Extension... Hookes Law

We need to think about the form

F = k∆L

Where the force is related by a constant for the spring.

Mr Powell 2012Index

Mass Distance


Example Results for one spring

Extension (m) Force (N)

0.000 0

0.035 1

0.090 2

0.175 3

0.254 4

0.000 0.050 0.100 0.150 0.200 0.250 0.3000

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Force (N)

Extension (m)

Forc

e (N

)

Mr Powell 2012Index

Mass Distance


Research...

Mr Powell 2012Index

Mass Distance


Variables....

Mr Powell 2012Index

Mass Distance


Write your Exp up in “Prose”

Mr Powell 2012Index

Mass Distance


What do these graphs show?

TASK: On your whiteboard describe each trend as clearly as you can

iii

Mr Powell 2012Index

Mass Distance


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)

Mr Powell 2012Index

Mass Distance


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?

Mr Powell 2012Index

Mass Distance


Adele

Bacteria growth

killed

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!

Mr Powell 2012Index

Mass Distance


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)

Mr Powell 2012Index

Mass Distance


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)

Forc

e ap

plie

dDiameter of lobe hole

Mr Powell 2012Index

Mass Distance


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)

Forc

e ap

plie

dExtension

CA Preparation “Stretching” Mr D Powell. Mr Powell 2012 Index Mass Distance Temperature Length Newton's Time Velocity pH Concentration Planning an Experiment.

Documents

mr powell

variables basic

mr d powell slide

basic trend

basic identifying variables

harder slide

spring constant

elastic object