Transcript 3. Energy and Movement - science

17 July 2015
Kinetic Energy
Objectives
Understand what factors increase kinetic energy.
Be able to use the equation for KE.
HSW: AF3 – Communicating and collaborating in science
Used before in: 2.1
Will use again in:
PLTS: Team workers – Work collaboratively with others.
Used before in: Science A
Will use again in:
Keywords: mass, velocity, squared, energy, Joule, m/s,
kg
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Outcomes
• ALL MUST be able to describe what
kinetic energy is and be able to carry out a
practical to calculate it.
• MOST SHOULD be able to describe how
GPE can be converted into KE.
• SOME COULD analyse a graph and
explain its shape. (HSW)
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Feeling energetic?
Who has the most kinetic energy: Rita or the cat?
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What is kinetic energy?
The word ‘kinetic’
comes from the
Greek word ‘kinesis’,
meaning motion.
Kinetic energy is the
energy an object has
because it is moving.
All moving things have kinetic energy, but the amount of
energy they have is not just dependent on how fast they
are moving.
What other factors affect the kinetic energy of a
moving object?
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How is kinetic energy calculated?
The kinetic energy (KE) of an object can be calculated using
this equation:
KE = ½ x mass x velocity2
= ½mv2
 Mass is measured in kilograms (kg).
 Velocity is measured in metres per second (m/s).
 KE is measured in joules (j).
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Calculating kinetic energy question
A car with a mass of
1,500 kg travels at a
velocity of 20 m/s.
What is the kinetic
energy of the car?
kinetic energy = ½ x mass x velocity2
= ½ x 1,500 x 202
= 300,000 J = 300 kJ
Now try the sheet of KE questions sheet
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Gravitational Energy to Kinetic Energy
• If clip doesn’t work click here: video
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Is that clip possible? Is it real?
• How would you go about setting this up?
• How would you know where to put the
paddling pool?
• What would you need to know?
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The relationship between GPE and KE
The law of conservation of energy means that as an object
falls, the GPE it loses must turn into a different form.
GPE lost = KE gained
This is only true if air resistance
and friction are ignored.
In reality, GPE would also be
transferred into heat and sound
energy so the KE of
rollercoaster would be less than
the GPE lost.
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Energy transfer of rollercoasters
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PRACTICAL TIME
• GPE TO KE
• Method
• AIM: to find out how the kinetic energy of a trolley depends on its
speed.
• For each starting position:
measure the height of the trolley above the runway.
use a motion sensor light gates to measure speed at the bottom of the
ramp.
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•
•
•
•
•
•
Measure the mass of the trolley.
Calculate the gravitational potential energy for each height.
Release the trolley and record the speed at the bottom of the ramp.
Repeat the test for different starting heights.
Record all your measurements in the table.
Plot a graph of initial gravitational energy against (speed)2.
Discuss the conclusions to be drawn from your results.
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Sample results
Height (m)
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Gravitational
Energy (J)
Speed Speed2
(m/s)
(m2/s2)
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graph
Speed2
3.5
3
2.5
2
Speed2
1.5
1
0.5
0
0
500
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1000
1500
2000
2500
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