Transcript 2008 Coaches Institute Presentation

Physics Lab
Leslie Watkins
Guilhem Ribeill
NCSO Coaches’ Clinic 2008
Overview/ Rules
• A team of up to 2 students will compete in lab
activities in the areas of work, energy, and
power.
Overview/ Rules
• A team of up to 2 students will compete in lab
activities in the areas of work, energy, and
power.
• Approximate time: 50 minutes
Overview/ Rules
• A team of up to 2 students will compete in lab
activities in the areas of work, energy, and
power.
• Approximate time: 50 minutes
• Students may bring and use any nonprogrammable calculator. No other resource
materials or electronic devices may be used
unless provided by the event supervisor.
Overview/ Rules
• The competition will consist of experimental
tasks and questions related to energy and
alternative energy.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Skills
• Students are expected to know concepts,
definitions and basic equations for work,
kinetic energy, gravitational potential energy,
spring potential energy, power, electric
energy stored in capacitors, electrical power,
heat produced in electrical resistance, work
done by fluids, fluid power, rotational work,
rotational power, efficiency of conversions
based on work, energy, and power.
Summary of Equations
Skills
• All answers are to be provided in SI units (such
as Watt, Joule, kilogram, meter, and second)
with proper significant figures. The event
supervisor will provide any equation beyond
those the students are expected to know.
Skills
• All answers are to be provided in SI units (such
as Watt, Joule, kilogram, meter, and second)
with proper significant figures. The event
supervisor will provide any equation beyond
those the students are expected to know.
• Students may be asked to collect data using
equipment that has been provided, set-up,
and demonstrated by the supervisor.
Sample Stations
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Electrical Energy to Mechanical Energy (Motors)
Electrical Energy to Electrical Energy (Transformers)
Solar Energy to Electric Energy (Photovoltaic Cells)
Gravitational Energy to Kinetic Energy
Rotational Energy to Gravitational Potential Energy
Pressure/ Volume Change to Kinetic and/or Gravitational
Potential Energy
Spring Energy to Kinetic and/or Gravitational Potential
Energy
Wind Energy to Electric Energy
Energy stored in Capacitor to Mechanical Energy
Efficiency of collisions (eg. Bouncing ball)
Problem-Solving Techniques
1)
2)
3)
4)
5)
Identify/Visualize The Problem
Determine Input Values
Determine the Appropriate Equation
Compute output
Check solution
Visualizing the Problem
• Ask yourself: “what’s really going on here?”
• It’s usually VERY important to draw the
problem!
Checking Your Answer
• Does my answer make sense?
- if you find the mass of the earth to be 12
grams, you probably did something wrong!
• Units, units, units, units!
- almost everything in physics has units – are
yours the right ones? If not, something might
have gone wrong!
An example!
A photovoltaic cell with an area of 2 m2 is used
to power a heater. The heater is a large 75 Ω
resistor which draws one 2A of current. If the
photovoltaic cell is 10% efficient, how much
power is the solar cell receiving from the sun?
Solution
1) Draw a picture!
2) Which equation is relevant? P = I2R for the resistor (heater)
3) Compute: P = (2A)(75Ω) = 150 W produced by the cell
4) If the cell is 10% efficient, then the sun must be producing
150W/0.1 = 1500 W of power
Example, Continued
Now supposed we’re asked to find how much
energy the sun delivers to the earth’s surface
per square meter per day.
Example, Continued
Now supposed we’re asked to find how much
energy the sun delivers to the earth’s surface
per square meter per day.
But we don’t have an explicit equation for this!
Example, Continued
Now supposed we’re asked to find how much
energy the sun delivers to the earth’s surface
per square meter per day.
But we don’t have an explicit equation for this!
Stay cool. We’ll use Dimensional Analysis
Example, Continued
Now supposed we’re asked to find how much
energy the sun delivers to the earth’s surface
per square meter per day.
But we don’t have an explicit equation for this!
Stay cool. We’ll use Dimensional Analysis
Dimensional Analysis? What’s that?
Dimensional Analysis?
Dimensional analysis is using the units as clues
to figuring out the appropriate equation.
Since all physical quantities have units, by
looking at the units of the input and output,
we often figure out what to do without having
to remember complicated equations
This can save a lot of time!
Dimensional Analysis!
The sun delivers 1500 W of power to a 2 m2 solar cell.
Well, we want the energy per square meter. So let’s divide to
get W/m2.
The sun delivers 750 W/m2 of power to the solar cell.
Okay. A watt is a joule per second. So if I want an answer in
joules, I need to multiply by seconds. There are 3600 seconds
in an hour, 24 hours in a day.
1500 J/s
3600 s
24 h
2 m2
1h
1 day
6,480,000 J
The sun delivers 6.48 x 106 J to a square meter of the earth’s
surface in a day!