13 April 2015
Conservation of Energy
Objectives
Be able to describe what the Conservation of Energy is
and understand that as energy is transferred it gets
spread out.
HSW: AF5: Explain ways of modifying work to improve accuracy and precision.
Used before in:
Will use again in:
PLTS: Independent enquirers: analyse and evaluate information, judging its relevance and value
Used before in:
Will use again in:
Keywords
Wasted, dissipated, directly proportional, accuracy, precision.
Outcomes
• All students should be able to describe
what the principle of conservation of
energy is.
• Most students should be able to
describe an example when, as energy is
transformed it gets spread out and more
difficult to use.
• Some students should be able to
describe how to make the experiment
more accurate and precise.
Braniac pendulum
• http://www.youtube.com/watch?v=ZbCLAZ
SPLNk&p=CAB44595BDD39B39&playnex
t=1&index=5
Conservation of Energy
In any energy change there is ALWAYS some “waste” energy:
e.g. a light bulb:
Electricity
Light
+
heat
In this example HEAT is wasted and it is transferred to
the surroundings, becoming very difficult to use.
Describe the following energy changes and state the “waste”
energy or energies:
1) A vacuum cleaner
2) A TV
3) A dynamo/generator
• Energy is measured in
………………(J)
Energy cannot be created or destroyed. It can
only be ……………… from one form to another
form.
• In other words Energy is always…………...
• When energy is transferred and/or transformed
only part of it may be ………… transferred/
transformed, the rest is …………….
• Energy will eventually be transferred to the
……………… which will get …………..
Joules
surroundings
wasted
conserved
transformed
usefully
warmer
Practical Time!!
Bungee jumping
• Aim
• To find out how much energy a bungee
jumper loses in one jump as a percentage of
their initial energy.
Bungee!!!!
• http://www.youtube.com/watch?v=lAZIxuxj
ogI
• Part 1
• In one jump, a bungee jumper starts and finishes with
gravitational potential energy.
• The change of gravitational potential energy of a
bungee jumper is proportional to the change of height
between the lowest and highest position.
• Use a suitable object on an elastic band as the
bungee jumper.
• Repeat your test several times to check the reliability
of the measurements. Record all your measurements
in a table.
• Use your measurements to work out the percentage of
the initial energy the jumper has after one complete
jump.
Initial
Height
Bungee Jump Practical
Analysis and Evaluation
Final Height
1
2
3
Average
% of
original
height
((final height/initial
height)x100)
• Part 3
• Draw an energy transfer diagram for the Bungee Jumper.
• Explain the energy changes that take place during one
complete jump and what type of energy is lost.
• Part 4
• Evaluate experiment by explaining how the method or
equipment used could be changed to make it more accurate
and precise.
Plenary - The Big Q: how can we improve
accuracy and precision?
•
A lightbulb maker claims that its 100 Watt bulb gives off 20 Joules of light per
second. The student uses the set up below to heat up some water and measure
the change in temperature of water over a ten minute period to calculate the
heat energy it gives off.
thermometer
From her calculations, she finds that the water receives 50
Joules of Heat energy every second.
All: What is the conservation of energy?
Most: Why does she measure the heat given off, when the
claim was made about light? Explain by using the
conservation of energy.
Some: Look at the student’s experiment; describe how she
could have changed it to make her results more accurate.
What could she have done differently to make the experiment
more precise?